Relationships between shoot and root growth of cucumber

 Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: 


you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. RELATIONSHIPS BETWEEN SHOOT AND ROOT GROWTH OF
CUCUMBER(fUC~~Li
SATIVUS L.) PLANTS UNDER VARIOUS
ENVIRONMENTAL STRESSES
A Thesis
Submitted in partial fulfillment
of the requirements for the degree
of
Doctor of Philosophy
in the University of Canterbury
by
G.C.
.
CHUNG
Lincoln College
1983
i i
Abstract of a thesis submitted in partial fulfillment of the
requirements for the Degree of Doctor of Philosophy
RELATIONSHIPS BETWEEN SHOOT AND ROOT GROWTH OF
CUCUM BE R( CuCUM ISS AT I VUS L.) PLAN TSUN DER "A,~ I OU S
ENVIRONMENTAL STRESSES
by
G.C.
CHUNG
The response of cucumber(Cucumis sativus L.) plants to
various
root
and
shoot
environments(solution
depth,
temperature, ionic strength, nitrogen and calcium level and
light intensity) were studied. Cucumber plants were grown in
continuously circulating-solution in a heated-glasshouse. Dry
weights of leaves, stems and roots, leaf area, leaf number,
root length and root number were measured as well as uptake of
potassium, calcium and nitrogen.
The relationship between
shoot and root in terms of functional equilibrium equations
was also examined. .The
results presented show that;
,
1. Shoot growth of cucumber plants was reduced
solutions of less than 50mm in depth.
if
grown
in
2. When roots were grown in shallow solution depths at 1 or
5mm the dry weight allocated to the root increased. The ratio
of root number/root length(no./cm) also increased.
Lowering
solution temperature to 12.5±2.5'C enhanced the production of
root number relctive to root length, and 5 and 2% of full
strength and 5% of full strength nitrogen level solution
stimulated the growth of root l~ngth relative to root number.
3. Under low
maintained at
strength and
growth was at
solution temperature treatment leaf number was
the expense of leaf area. Under low. total ionic
low nitrogen solution, enhanced root length
the expense of leaf area growth.
iii
4. Low solution temperature enhanced the dry weight allocated
to the stem relative to the leaf. Low total ionic strength
and low nitrogen solution increased the dry weight allocated
to the leaf relative to the stem.
5. The specific activity of root, represented by specific
absorption rate, increased when the shoot was under light
stress and, the specific activity of shoot, represented by
increased
when the root was under
unit
shoot
rate,
nitrogen-stress.
6. The form of equation developed by Thornley(~M = fm~W,
where ~M is the increment in weight of element M and ~W the
increment in total plant dry weight during a time period ~t
with fm a constant) showed a better relationship than the
equation developed by Davidson[root mass x rate(absorption) a
leaf mass x rate(photosynthesis)J and subsequently used by
Hunt in the form of mass ratio(root/shoot) a l/activity ratio.
The equation developed by Chung et al,
total plant weight/(leaf number/leaf area) a total "k"/(root
number/root length),
where k represents the total contents of
elements
or
compounds, showed a good approximation of the relationship
between shoot and root under all the environmental stresses
imposed with the exception of calcium uptake.
7.
The results support the concept that the activity of the root
or shoot in carrying out its function is influenced by the
demand created by the opposite organ and appears to be a
better assumption than that which proposes that the activity
of an organ is solely dependent on its own size.
KEYWORDS:
Cucumber(Cucumis sativus L.);
solution depth;
solution
temperature;
ionic strength;
light intensity;
nitrogen and calcium level; '"' shoot;
root;
morphology;
functional equilibrium equations; nutrient film technique
iv
/
CERTIFICATE
I hereby certify that the
e~perimental
work contained
in this thesis was planned, executed and described by
the candidate, under the direct supervision of
Professor R.N. Rowe and Dr R.J. Field.
R. N. Rowe
(Supervisor)
...
v
TABLE OF CONTENTS
HEADING
ABSTRACT
LIST OF TABLES AND PLATE
LIST OF FIGURES
LIST OF EQUATIONS
CHAPTER 1
GENERAL INTRODUCTION
CHAPTER 2
MATERIALS AND METHODS
2.1. Experimental design and nutrient
solution-circulating system
2.2. Measurement of shoot and root morphology
2.2.1. Measurement of shoot morphology
2.2.2. Measurement of root morphology
2 . 3 • Chemical analysis of plant samples
2.4. The use of Richards function in
curve-fitting
2 • 5 • Experiments
2.5.1.
Expt. 1. Effect of depth of solution
2.5.2.
Expt. 2. Effect of solution
temperature
2.5.3. Expt.
3.
Effect of solution
temperatu re and depth
2.5.4. Expt.
4.
Effect of solution ionic
strength, depth and volume
2.5.5. Expt.
5.
Effect of solution ionic
strength and 1 i gh t intensity
2.5.6. Expt.
6.
Effect of nitrogen and
calcium level
PAGE
ii
vii
vii i
x vii i
1
4
4
9
9
9
11
11
12
12
13
13
14
14
15
vi
HEADING
CHAPTER 3
EQUATIONS FOR THE FUNCTIONAL EQUILIBRIUM
RELATIONSHIP BETWEEN SHOOT AND ROOT
3.1. Introduction
3.2. Results using the functional equilibrium
equations
3.3. USR, SAR and shoot/root ratio
3 .4. Root number/root length ratio
3 . 5 • Stem weight and leaf weight ratios
3 .6. Root length/leaf area and
root number/leaf number ratios
3 • 7 • Discussion
CHAPTER 4
THE IMPLICATION OF SOURCE-SINK
RELATIONSHIPS ON THE FUNCTIONAL
EQUILIBRIUM RELATIONSHIP BETWEEN
SHOOT AND ROOT
4.1. Introduction
4.2. Results
4.3. Discussion
CHAPTER 5
AGRONOMIC IMPLICATIONS
CONCLUSIONS
ACKNOWLEDGEMENTS
REFERENCES
APPENDIX I
APPENDIX I I
APPENDIX I I I
APP~NDIX IV
APPENDIX V
APPENDIX VI
PAGE
16
16
26
68
84
89
103
110
124
124
132
142
151
158
160
161
175
176
177
178
179
180
vii
LIST OF TABLES AND PLATE
TABLE
Table 2.1. Composition of nutrient solution.
PAGE
7
Table 3.1. Potassium percentage of leaves treated
at
different solution temperatures.
45
Table 3.2. Potassium percentage of leaves treated
at
different solution temperatures
and depths.
46
PLATE
Plate 2.1. Nutrient solution-circulating system used
in the glasshouse.
5
vii i
LIST OF FIGURES
FIGURE
Fig. 2.1.
Fig. 2.2.
Fig. 3.1.
Fig. 3.2.
Fig. 3.3.
Fig. 3.4.
Fig. 3.5.
Fig. 3.6.
PAGE
Diagram indicating the layout of
the nutrient solution-circulating
system.
6
Diagram indicating the control of
water level in the header tank.
8
The effect of different solution
temperatures on the relationship
between the mass ratio and the
reciprocal of activity ratio
with respect to potassium uptake.
27
The effect of different solution
temperatures on the relationship
between the mass ratio and the
reciprocal of activity ratio
with respect to calcium uptake.
28
The effect of different solution
temperatures on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to nitrogen uptake.
29
The effect of different solution
temperatures on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to sum of potassium,
calcium and nitrogen uptake.
30
The effect of different solution
temperatures on the relationship
between plant dry weight and total
potassium content.
32
The effect of different solution
tem~eratures on the relationship
between plant dry weight and total
calcium content.
33
ix
FIGURE
Fig. 3.7.
Fig. 3.8.
Fig. 3.9.
PAGE
The effect of different solution
temperatures on the relationship
between plant dry weight and total
nitrogen content.
34
The effect of different solution
temperatures on the relationship
between plant dry weight and total
sum of potassium, calcium and
nitrogen content.
35
The effect of different solution
temperatures on the relationship
between plant dry weight/(leaf
number/leaf area) and total potassium
content/(root number/root length).
37
Fig. 3.10. The effect of different solution
temperatures on the relationship
between plant dry weight/(leaf
number/leaf area) and total calcium
content/(root number/root length).
38
Fig. 3.11. The effect of different solution
temperatures on the relationship
between plant dry weight/(leaf number/
leaf area) and total nitrogen content/
(root number/root length).
39
Fig. '3.12. The effect of different solution
temperatures on the relationship
between plant dry weight/(leaf number/
leaf area) and total sum of potassium,
calcium and nitrogen content/(root
number/root length).
40
Fig. 3.13. The effect of different solution
temperatures and depths on the
relationship between the mass ratio
and the reciprocal of activity ratio
with respect to sum of potassium and
calcium uptake in the shoot.
42
x
FIGURE
Fig. 3.14. The effect of different solution
temperatures and depths on the
relationship between plant dry weight
and total sum of potassium and calcium
uptake in the shoot.
PAGE
43
Fig. 3.15. The effect of different solution
temperatures and depths on the
relationship between plant dry weight/
(leaf number/leaf area) and the total
sum of potassium and calcium in the shoot/
(root number/root length).
44
Fig. 3.16. The effect of different solution ionic
strengths, depths and volumes on the
relationship between the mass ratio and the
reciprocal of activity ratio with respect
to sum of potassium and calcium uptake.
48
Fig. 3.17. The effect of different solution ionic
strengths, depths and volumes on the
relationship between plant dry weight
and total sum of potassium and calcium
content.
49
Fig. 3.18. The effect of different solution ionic
strengths, depths and volumes on the
relationship between plant dry weight/
(leaf number/leaf area) and the total
sum of potassium and calcium/
(root number/root length).
50
Fig. 3.19. The effect of different solution ionic
strengths and light intensities on the
relationship between the mass ratio and
the reciprocal of activity ratio with
respect to sum of potassium and calcium
and nitrogen uptake.
52
xi
FIGURE
Fig. 3.20. The effect of different solution ionic
strengths and light intensities on the
relationship between plant dry weight
and total sum of potassium, calcium
and nitrogen content.
PAGE
53
Fig. 3.21. The effect of different solution ionic
strengths and light intensities on the
relationship between plant dry weight/
(leaf number/leaf area) and total sum of
potassium, calcium and nitrogen content/
(root number/root length).
54
Fig. 3.22. The effect of different levels of
nitrogen and calcium on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to potassium uptake.
56
Fig. 3.23. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight and total
potassium content.
57
Fig. 3.24. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight/(leaf number/
leaf area) and total potassium content/
(root number/root length).
58
Fig. 3.25. The effect of different levels of
nitrogen and calcium on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to calcium uptake.
59
Fig. 3.26. The effect of different levels of
nitrogeri and calcium on the relationship
between plant dry weight and total
calcium content.
60
xii
FIGURE
Fig. 3.27. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight/(leaf number/
leaf area) and total calcium content/
(root number/root length).
PAGE
61
Fig. 3.28. The effect of different levels of
nitrogen and calcium on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to nitrogen uptake.
62
Fig. 3.29. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight and total
nitrogen content.
63
Fig. 3.30. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight/(leaf number/
leaf area) and total nitrogen content/
(root number/root length).
64
Fig. 3.31. The effect of different levels of
nitrogen and calcium on the relationship
between the mass ratio and the
reciprocal of activity ratio with
respect to sum of potassium, calcium
and nitrogen uptake.
65
Fig. 3.32. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight and total sum
of potassium, calcium and nitrogen
content.
66
xii i
FIGURE
Fig. 3.33. The effect of different levels of
nitrogen and calcium on the relationship
between plant dry weight/(leaf number/
leaf area) and total sum of potassium,
calcium and nitrogen content/(root
number/root length).
Fig. 3.34. The effect of different solution
temperatures on the USR.
PAGE
67
69
Fig. 3.35. The effect of different solution ionic
strengths, depths and volumes on the USR.
70
Fig. 3.36. The effect of different solution ionic
strengths and light intensities on
the USR.
71
Fig. 3.37. The effect of different levels of
nitrogen and calcium on the USR.
72
Fig. 3.38. The effect of different solution
temperatures on the SAR.
74
Fig. 3.39. The effect of different solution ionic
strengths, depths and volumes on the SAR.
75
Fig. 3.40. The effect of different solution ionic
strengths and light intensities on the
SAR.
76
Fig. 3.41. The effect of different levels of
nitrogen and calcium on the SAR.
77
Fig. 3.42. The effect of different solution depths
on the shoot/root ratio.
79
Fig. 3.43. The effect of different solution
temperatures on the shoot/root ratio.
80
Fig. 3.44. The effect of different solution ionic
strengths, depths and volumes on the
shoot/root ratio.
81
xiv
FIGURE
Fig. 3.45. The effect of different solution ionic
strengths and light intensities on the
shoot/root ratio.
PAGE
82
Fig. 3.46. The effect of different levels of
nitrogen and calcium on the shoot/root
ratio.
83
Fig. 3.47. The effect of different solution depths
on the root number/root length ratio.
85
Fig. 3.48. The effect of different solution
temperatures on the root number/root
length ratio.
86
Fig. 3.49. The effect of different solution ionic
strengths and light intensities on the
root number/root length ratio.
87
Fig. 3.50. The effect of different levels of
nitrogen and calcium on the root
number/root length ratio.
88
Fig. 3.51. The effect of different solution depths
on the stem weight ratio.
90
Fig. 3.52. The effect of different solution
temperatures on the stem weight ratio.
91
Fig. 3.53. The effect of different solution
temperatures and depths on the stem
weight ratio.
92
Fig. 3.54. The effect of different solution ionic
strengths, depths and volumes on the
stem weight ratio.
93
Fig. 3.55. The effect of different solution ionic
strengths and light intensities on the
stem weight ratio.
94
xv
FIGURE
Fig. 3.56. The effect of different levels of
nitrogen and calcium on the stem weight
ratio.
PAGE
95
Fig. 3.57. The effect of different solution depths
on the leaf weight ratio.
96
Fig. 3.58. The effect of different solution
temperatures on the leaf weight ratio.
97
Fig. 3.59. The effect of different solution
temperatures and depths on the leaf
weight ratio.
98
Fig. 3.60. The effect of different solution ionic
strengths, depths and volumes on the
leaf weight ratio.
99
Fig. 3.61. The effect of different solution ionic
strengths and light intensities on the
leaf weight ratio.
100
Fig. 3.62. The effect of different levels of
nitrogen and calcium on the leaf
weight ratio.
101
Fig. 3.63. The effect of different solution
temperatures on the root length/leaf
area ratio.
104
Fig. 3.64. The effect of different solution ionic
strengths and light intensities on the
root length/leaf area ratio.
105
Fig. 3.65. The effect of different levels of
nitrogen and calcium on the root
length/leaf area ratio.
106
Fig. 3.66. The effect of different solution
temperatures on the root number/leaf
number ratio.
107
FIGURE
Fig. 3.67. The effect of different solution ionic
strengths and light intensities on the
root number/leaf number ratio.
Fig. 3.68. The effect of different levels of
nitrogen and calcium on the root
number/leaf number ratio.
Fig. 4.1.
Fig. 4.2.
Fig. 4.3.
Fig. 4.4.
PAGE
108
109
Model for communication and coupling
between shoot and roots drawn by Luttge
and Higinbotham(1979) after Cram and
Pitman(1972) and Pitman(1972).
128
The effect of different solution ionic
strengths, depths and volumes on the
relationship between the shoot/root ratio
and the reciprocal of activity ratio with
respect to sum of potassium and calcium
uptake.
133
The effect of different solution ionic
strengths and light intensities on the
relationship between the shoot/root
ratio and the reciprocal of activity
ratio with respect to sum of potassium,
calcium and nitrogen uptake.
134
The effect of different solution
temperatures on the relationship between
(plant weight) x (root weight) x (root
weight) and the (total sum of potassium,
calcium and nitrogen) x (shoot weight) x
(shoot weight).
136
x vii
FIGURE
Fig. 4.5.
PAGE
The effect of different solution ionic
strengths and depths on the relationship
between (plant weight) x (root weight) x
(root weight) and the (total sum of
potassium and calcium) x (shoot weight) x
(shoot weight).
137
Fig. 4.6.
The effect of different solution ionic
strengths and light intensities on the
relationship between (plant weight) x
root weight) x (root weight) and the (total
sum of potassium, calcium and nitrogen) x
(shoot weight) x (shoot weight).
138
Fig. 4.7.
The effect of different levels of
nitrogen and calcium on the relationship
between (plant weight) x (root weight) x
(root weight) and the (total sum of
potassium, calcium and nitrogen) x (shoot
weight) x (shoot weight).
139
The effect of different levels of
nitrogen and calcium on the relationship
between the shoot/root ratio and the
reciprocal of activity ratio with
respect to calcium uptake.
140
Fig. 4.8.
Fig. 4.9.
The effect of different levels of
nitrogen and calcium on the relationship
between (plant weight) x (root
weight) x (root weight) and the (calcium
content) x (shoot weight) x (shoot weight). 141
x vii i
LIST OF EQUATIONS
EQUATION
Equation 2.1.
Equation 3.1.
Equation 3.2.
Equa t ion 3. 3 •
Equation 3.4.
Equation 3.5.
Equation 4.1.
Equation 4.2.
Equation 4.3.
Equation 4.4.
Equation 4.5.
Equation 4.6.
Equation 4.7.
Equation 4.8.
PAGE
W=A(1±e(b-kt))-i,
12
Root mass x rate(absorption) a leaf
16
mass x rate(photosynthesis)
Mass ratio(root/shoot) aI/activity
16
ratio
18
L1M = f mL1W
Source strength = source size x
18
source activity
Plant weight/(leaf number/leaf
area) a total "k"/(root number/root length) 21
Shoot mass x specific root activity =
total root activity
129
Root mass x specific shoot activity =
total shoot activity
129
Shoot mass x specific root activity a
129
root mass x specific shoot activity
129
Shoot/root ratio a l/activity ratio
(Plant weight/shoot weight/day) x root
weight a ("K"/root weight/day) x
130
shoot weight
(Plant weight) x (root weight) x (root
weight) a ("K") X (shoot weight)
130
x (shoot weight)
b
Y=aX
1~;p
log(y)=log(a) + b·log(x)
131
~;(
1
CHAPTER 1
GENERAL INTRODUCTION
The ability of plants
unfavourable
adapt
to
to
environmental stresses is vital for their survival. Of the
expressions describing the degree of adaptibility of plants to
various soil and atmospheric environments the most convenient
and frequently used is the ratio of
shoot
to
root
weight(Boote, 1977;
Ledig and Perry, 1965). The general
consensus is that a higher proportion of dry weight is
allocated to the part of the plant whose function is under
stress. This type of response can be readily and directly
seen by artificial manipulation of shoot and root systems such
as root pruning(Andrews and Newman, 1968;
Cooper, 1971;
McDavid et al, 1973), the effects of defoliation on root
establishment of grasses and clovers(Evans, 1977) in response
to frequent animal grazing(Harradine and Whalley, 1981) and
the effects of drought on plants grown in
arid
land
zones(Hodgkinson
and
Baas
Becking,
1978).
Such
an
inter-dependence or competition between shoot and root implies
that their functions can not really be separated when studying
growth of the whole plant system(Russell, 1977). Moreover, it
is clear that hormones produced both in the shoot and root may
take part
in
the
coordination
of
shoot
and
root
function(Clarkson and Gerloff, 1979; Vaadia and Ita;, 1969) •
. Davidson(1969a, 1969b) proposed an equation(see page 16,
equation
3.1),
resulting
in the proposition that the
partitioning of photosynthate is controlled
in
inverse
proportion by the relative rates of photosynthesis of the
leaves and the absorption of water and nutrients by the roots.
His reasoning is that externally induced reduction in the
specific activities of root or shoot function would tend to be
compensated by increases in the mass of the same component in
order to maintain its total activity.
This hypothesis is
supported by others(Charles-Edwards, 1976, 1982; Cooper and
Thornley, 1976; Hunt, 1975, 1976; Hunt and Burnett, 1973;
Hunt et al, 1975; Richards, 1977, 1978, 1981; Richards et
2
al, 1979b; Thornley, 1972, 1976) although different authors
have derived their evidence based on either mechanistic or
empirical modelling approaches. All have accepted that an
equilibrium ~xists between the shoot and root functions.
The equation proposed by Davidson(1969a, 1969b) and
subsequently
used
by
Hunt(1975)
is analogous to the
source-sink
relationship
equation
proposed
by
Warren-Wilson(1972,
see
page
18, equation 3.4).
What
Davidson's equation essentially proposes is that
source
strengths of shoot and root are proportional to each other.
Lack of universal acceptance of the Davidson's(1969a,
1969b) equation describing the relationship between shoot and
root function results from the following.
1.
The shoot/root ratio is based on the weight, i.e.
functional sizes are represented by the dry weights of each
organ, and completely ignore any possible contribution of
morphological and anatomical aspects of shoot and root, which
may affect the efficiency of functions.
2. Davidson's(1969a, 1969b) equation assumes that ion uptake
is a function of the ion concentration in the external
solution and never exceeds the maximum affinity represented by
the Michaelis-Menten constant.
Therefore, the concept of
metabolic demand in one organ being the "driving force" of
function in the opposite organ as suggested by Nye and
Tinker(1969) is not considered in the concept
of
the
functional equilibrium equation between shoot and root.
3. There have been serious arguments between~ mechanistic and
empirical modellers(see page 22-23) on the ways of expressing
the equations. However, no one has really looked into the
biological significance of the equations under a wide range of
environmental stresses.
The series of experiments reported in this thesis
was
designed to test the validity of existing equations on the
functional equilibrium between shoot and root, including the
empirical equation(see page 21, equation 3.5) proposed by
Chung et al(1982). Furthermore, the ways in which the demand
concept may be included in the equilibrium equation were also
sought.
3
Since all the experiments were designed to test the
validity of three existing equations, this thesis is arranged
in such a way that all the materials and methods used are
described in Chapter 2, followed by the detailed discussion of
results of five experiments using equations 3.2, 3.3 and 3.5
in Chapter 3. Chapter 4 is primarily concerned with using all
the experimental data excluding that from Expt. 1 to derive
equations in which the implication of feedback mechanisms
between shoot .and root are included.
Most of the general
discussion is devoted to discussing the agronomic implication
of the results.
4
CHAPTER 2
MATERIALS AND METHODS
2.1.
Experimental design and nutrient
solution-circulating system
Cucumber(Cucumis sativus L., CV Special Hybrid No.2) was
used throughout the series of experiments as experimental
material. In all experiments, growth was restricted to the
vegetative form by removing female flowers as they appeared.
The
plant
growing
system
was
set
up
in
a
temperature-controlled glasshouse(18·C and 30·C) as shown in
Plate 2.1 and Fig. 2.1. Nutrient solution(Cooper, 1975, see
solution formulation on page 7) was continuously circulated by
a submersible pump inside the header tank.
Black polythene
pipe(5cm diameter) was laid on the ground as a main delivery
system into which
lateral
pipes(I.4cm
diameter)
were
connected. Plastic fittings were used to connect the laterals
to each pot. There were 20 pots in each row, totalling 40
pots in each closed system. Spacing within and between a row
was 60cm by 90cm. The capacity of each pot was approximately
4.5 litres, and there was 250 litres of solution in each
closed system. Supplementary lighting was not provided but
air movement was facilitated by air heating and ventilation.
Seeds were sown in plastic trays in sand and kept in the
glasshouse under mist with bottomheat(24±2·C). Seedlings
were fed with a commercial liquid feed solution(Lush).
When
the
cotyledons were fully expanded, the seedlings were
transferred to the individual lidded pots. Plants were held
in position by polystyrene that covered the hole in the lid.
Further aerial support to growing plants was given by string
runners where necessary.
Oxygen was supplied by continuous
aeration of each pot.
It was essential to maintain a continuous solution depth
of 1mm and 5mm for Expts. 1, 3 and 4. A simple levelling
device was used in controlling the water inlet, which proved
satisfactory.
Water
lost by
evapotranspiration was
5
Plate 2.1
Nutrient solution - circulating system used in
the glasshouse.
5.T,
I
~
T.W.
~
Jl
~
~
fll
H.T.
~
,1;
H.T.
H.T.
i
1
T
1
i
.'! 1
1
~
~
i
~
Fig. 2.1
Diagram indicating the layout of the nutrient solution-circulating
system.
T.W.: tap water; S.T.: storage tank for water; p: submersible pump;
H.T.: header tank; b.c.: ball-cock controlling water inlet;
c: container for individual plant.
(Arrows indicate the flow of water and nutrient solution).
(j)
7
replaced by an automatic metering system, shown in Fig.
2.2.
As the water level dropped, the float of the ball cock on the
surface of the solution in the header tank also dropped and
opened a valve. It was found that the solution level in each
pot was sensitive and constant in response to the height of
the ball cock.
Solution depth control was achieved by
adjustable stainless steel mesh trays that fitted in each pot
and were levelled by threaded aluminium rods. Using this
system it was possible to maintain constant solution depths,
as shallow as 1mm.
Basic nutrient solution composition used was the Cooper's
solution shown in Table 2.1 below.
Table 2.1. Composition of nutrient solution
ppm
117(N), 168(Ca}
254(K) , 91(N}
49(Mg)
62(P) , 78(K)
5.6(Fe)
2.2(Mn)
O.32(B)
O.065(Cu)
O.007(Mo)
23(P}
8
!
solution
1eve 1
!
~
P
tap water
inlet
"Fig. 2.2
,--_.-1---)-
nutrient
solution
inlet
nutrient
solution
outlet
Diagram indicating the control of water
levels in the header tank.
(B.C.: ball-cock;
P:submersiblepump).
9
The pH of the solution was maintained within the range of
6.0-6.5.
Conductivity
of
solution was monitored
the
throughout the experiment and more nutrients were added from
In general, a new
the basic solution whenever necessary.
solution was made up at weekly intervals to avoid the
excessive depletion of any particular ion.
2.2.
Measurement of shoot and root morphology
2.2.1.
Measurement of shoot morphology
Except in Expts. 1 and 3, all the lateral shoots were
left to grow.
The small axillary buds that were visibly
identifiable were also included when determining leaf number.
Leaf area was measured using a Licor model 3100 area
meter.
Dry weights of leaf and stem were measured after
drying at 80 C for 24 hours and cooling in a desiccator.
l
2.2.2.
2.2.2.1.
Measurement of root morphology
Preparation of root sample
As measuring the root morphology was time-consuming, it
became necessary to store the roots temporarily for subsequent
measurement. Immediately after harvesting the roots, they
were placed in a cooler at 2 C. Dry weight measurement showed
no degeneration of the samples when stored for up to one week.
1
Generally the root systems were so large that it was
necessary to use a subsampling method.
This was done
according to the technique used by Goubran and Richards(1979).
The total root system was first cut into small pieces using
scissors. A proportion was then transferred to a house-hold
blender with a capacity of 1 litre. Samples were cut into
about 5mm lengths by using a blender to cut and mix the roots.
The time required for this operation varied from 3-4 seconds
for thin roots to about 10 seconds for thick roots. The root
sample was then transferred and spread evenly over the base of
a water-filled galvanized iron tray(400 x 250 x 100mm) which
had poly-vinyl foam on the bottom covered with cotton cloth.
Reusable cotton cloth was found?to be more satisfactory than
blotting paper.
The water was removed by suction through
10
holes in a regular pattern in the bottom of the tray beneath
the foam.
Suction was provided by a water pump. After
removal of the water the cloth, over which the roots were
evenly spread, was placed on a graduated sheet marked with 50
equal rectangles. This graduated sheet formed the upper side
of a light box. Three sample lots randomly selected of 10%
from entire root sample was taken as recommended by Goubran
and Richards(1979);
one of each for measurement of root dry
weight, root length and root number, respectively.
Root
length and dry weight was measured immediately whereas the
sub-samples used for counting the root number were stored in a
5% formalin solution for measurement at later date.
2.2.2.2.
Measurement of root length and root number
by
A modification of Newman ' s(1966) method adapted
Evans(1970)
and Goubran and Richards(1979) was used to
determine the root length and root number.
Since cucumber
roots were mostly very fine, the thick(>2mm in diameter) and
suberized root were not separated.
The 10% sub-sample was
spread evenly on the cotton cloth and the water was removed by
a tap aspirator as described earlier. The cotton cloth with
roots was laid down on a sheet of plastic etched with 1cm grid
lines illuminated from beneath. All intersections of roots
and grid lines were counted on vertical and horizontal axis,
and the final root length was estimated by following formula,
R=~N/2
where N is the average number of intersection on the vertical
and .horizontal axis. This grid method was used until Expt.4
after which a root length scanner(Comair) described
by
Richards et al (1979a) became available and was used for Expts.
5 and 6.
The number of roots was estimated by counting the number
of branches. A single unbranched root has a single apex. If
it produces one lateral, then it has two roots. If there are
R roots with grand total of N branches, the total number of
root is R+N(Evans, 1970).
11
2.3.
Chemical analysis of plant samples
One hundred mg of oven-dried leaf and root material(80'c,
24hrs) was ignited in a crucible in a muffle furnace at 500'C
until completely ashed.
After cooling, 2ml ofl:l HCl
solution was added to each crucible. The digests were diluted
to 25ml with distilled water. The diluted digest was analysed
for K and Ca by atomic absorption spectrometry.
One hundred mg sample of oven-dried material(80'C, 24
hrs) for nitrogen analysis was digested in concentrated
sulphuric acid using potassium sulphate, copper sulphate and
selenium powder(10:1:0.1 mixture) catalysts by the normal
Kjeldahl technique. The digest was diluted to SOml with
distilled water.
A lSml aliquot was steam distilled in a
Markham still in the normal manner, the distillate being
collected in 10ml of boric acid containing Brown Cresol
Green/Methyl Red mixed indicator, and titrated with O.OlN
sulphuric acid.
2.4.
The use of Richards function in curve-fitting
In recent years considerable attention has been given to
the so-called functional approach as opposed to classical
growth analysis. A mathematical function is used to fit the
data and derive the various growth quantities such as relative
growth rate and unit leaf rate(=net assimilation rate). There
are advantages in using functional growth analysis as set out
by Causton and Venus(1981) and Hunt(1979).
Notably, fitted
mathematical functions provide a convenient summary of the
data and overcome problems in pairing of plants across harvest
intervals
as
done in the case of classical analysis.
Furthermore, if the function employed is based on some
biologically
useful
concepts,
then one may infer the
significance of constants obtained for different species or
different treatments on the same species(Causton et al, 1978),
There have been a few methodological approaches using fitted
functions(See Hunt, 1982 for various functions used). Among
them particular attention has been given to the Richards(1959)
function by Causton and Venus(1981) and others(Dennett et al,
1979; Venus and Causton, 1979).
12
The Richards function is desGribed as
1
W=A(l±e(b-kt))-n
---------2.1
where W is the value of a growth attribute at time t, A and k
are positive constants, and b is the constant of integration.
The constant A gives the asymptotic maximum size of the
growing system concerned and n defines the shape of the curve.
A FORTRAN program to fit Richards function developed by
Causton(1969), and kindly supplied by him, was used throughout
for curve-fitting. This program carries out the fitting of
the Richards function to leaf, stem, root dry weight and leaf
area and whole plant growth analysis using the
fitted
functions. Various parameters such as leaf weight ratio(LWR),
stem weight ratio(SWR), root weight ratio(RWR) and leaf area
ratio(LAR) are calculated as well as specific leaf area(SLA)
and unit leaf rate(ULR). In addition, shoot/root ratio, root
number/root length ratio, specific absorption rate(SAR) and
unit shoot rate(USR), root length/leaf area ratio and root
number/leaf number ratio were also calculated by fitting the
Richards function. Since the Richards function contains 4
parameters, it is impossible to fit the data with fewer than 5
harvests as Causton et al(1978) described.
Therefore, the
results of Expts.
3 and 4 where there were only 3 harvests
are presented with standard error of mean values at each
harvest.
For the Expts.
1, 2 and 5 where there were 4
harvests, the measurement made at the beginning of treatments
was included as first harvest.
2.5.
2.5.1.
Experiments
Expt.
1.
Effect of depth of solution
Seedlings grown in sand were transferred
to
pots
containing full strength Cooper ' s(1975) solution. Treatments
were imposed one week after transplanting when seedling growth
was established.
This technique was also applied th~oughout
all the experiments.
Solution depths
of
1,
5,
50,
170mm(control treatment, full depth of pot) were achieved by
stainless steel mesh trays as described earlier.
Solution
depths
were
randomly
allocated in each closed system
containing full strength of Cooper ' s(1975) solution.
Plants
13
were harvested 4 times at weekly intervals. At each harvest,
7 plants for each depth treatment were randomly chosen for
measurements of shoot and root weight and morphology.
2.5.2.
Expt.
2.
Effect of solution temperature
The size of the closed system was reduced from 40 to 20
pots
to
avoid
the
temperature
changes
within
the
circulating-solution. Solution temperature of 12.5±2.5 C was
achieved by immersing a refrigeration unit in the header tank
connected to a thermostat.
A heating element
with
a
thermostat switch was used to raise the solution temperature
to 32.5±2.5 C. All the pots were insulated with polystyrene.
The temperature differential along each row was no more than
±0.5 C.
All treatments received full strength
Cooperls
solution.
Because of poor plant growth due to low solution
temperature, plants grown at 12.5±2.5 c were harvested 4 times
at weekly intervals, with 4 replicates at each harvest whereas
plants grown at 32.5±2.5 C were harvested 7 times at half
weekly intervals with 3 replicates. As well as shoot and root
weight and morphology, K, Ca and N content of leaves and roots
were analysed according to the method described in Section
I
I
I
I
I
2.3.
2.5.3.
Expt.
3.
Effect of solution temperature and
depth
The same method adovted in Expts. 1 and 2 was used in
this experiment to control solution depths and temperatures.
Treatments imposed were 12.5±2.5 C, 22.5±2.5 C and 32.5±2.5 C
for
temperature
treatment and 5mm and 50mm for depth
treatments. Each header tank was allocated a temperature
level, feeding 36(+4 spare) plants.
Solution depths were
allocated completely randomly. At three harvest dates, and at
three week intervals, 6 plants from each temperature and depth
treatment were randomly chosen for harvesting. Shoot and root
weight, morphology and the content of K and Ca in the leaves
were measured.
I
I
I
14
2.5.4.
Expt.
4.
Effect of solution ionic strength,
depth and volume
3
depths and v§lumes respectively of 1mm(19.6cm ),
5cm(980cm) and 5cm(19.6cm ) were controlled by container size
and adjustable stainless steel mesh trays.
Three nutrient
solutions were used;
5 % and 2% of full strength nutrient
solution(Cooper, 1975) plus full strength as a control.
Each
header tank was allocated a nutrient solution ionic strength,
and solution depths and volumes were randomly allocated within
the closed system. At 3 harvest dates at 3 week intervals, 4
plants at each depth and volume treatment were randomly
harvested.
Total content of K and Ca as well as shoot and
root dry weight and morphology were measured.
Solu~ion
2.5.5.
Expt.
5.
Effect of solution ionic strength
and light intensity
Full strength and 5% nutrient solution(Cooper, 1975) were
used as main treatments. In each block, Sarlon shade cloth
was used to achieve an environment of either 50% or 10% of
natural light.
Since there was a huge difference in plant
growth depending on the different ionic strengths and light
intensities, it was necessary to harvest the plants at
differing intervals. Plants treated with full and 50% of full
light and full strength solution were therefore harvested 7
times at random, twice a week with 3 replicates whereas the
remaining treatments were harvested at random 4 times, once a
week with 4 replicates.
l~
2.5.6.
Expt.
6.
Effect of nitrogen and calcium level
A modification of Cooper ' s(1975) nutrient solution was
used to achieve different levels of nitrogen and calcium. The
same amount of nitrogen and calcium content in Cooper ' s(1975)
solution was replaced with ammonium nitrate and calcium
chloride to achieve the concentration of 5% of full strength
nitrogen
and calcium level respectively.
The remalnlng
elements were the same as the Cooper ' s(1975) solution shown in
Table 2.1.
Each header tank was allocated a full strength,
low-nitrogen ~nd low-calcium solution. At the 5 harvest dates
at one week intervals, 8 plants were randomly chosen for
measurement of shoot and root weights, morphology and K, Ca
and N content in the plants.
16
CHAPTER 3
EQUATIONS FOR THE FUNCTIONAL EQUILIBRIUM
RELATIONSHIP BETWEEN SHOOT AND ROOT
3.1.
Introduction
A functional equilibrium relationship between shoot and
root has been recognized by a number of researchers. The
rationale for this functional balance is that the shoot/root
ratio is sensitive to the ratio of nitrogen uptake(root
activity)
and
carbohydrate
synthesis
(shoot
activity)(Troughton,
1960).
This relationship has been
quantified by Davidson (1969a, 1969b) on the basis that the
partitioning of photosynthate is controlled by the relative
rates of photosynthesis and root absorption, in inverse
proportion, which gives the equation
root mass x rate(absorption)a leaf mass x
rate(photosynthesis)-------------------------3.1
This quantified relationship has been successfully used by
several authors (Hunt, 1975; Hunt and Burnett, 1973; Hunt et
al, 1975) in the form;
mass ratio aI/activity ratio----------------3.2
where mass ratio is the ratio of root to shoot dry weight and
the activity ratio is the ratio of specific absorption
rate(SAR) to the unit shoot rate(USR). The units used in the
present studies are gig for mass ratio and (g/g/day)/(g/g/day)
for activity ratio, respectively.
This inter-dependence of
shoot and root activities has been deduced from experiments
where var(ous stresses were imposed on the shoot and/or root.
Hunt
and
Burnett(1973)
concluded
that
perennial
ryegrass(Lolium ~~enne L.) treated with different light
intensities and potassium levels showed complementary changes
in the mass ratio and activity ratio, which could be expressed
by a single line relationship. Hunt(1975) also showed that
perennial ryegrass maintained a functional balance
with
differing"nitrogen levels and light intensities.
17
Raper et al (1978) proposed a model in which a balanced
inter-dependence between shoot function(carbohydrate supply)
and root function(nitrogen supply)
of
tobacco(Nicotiana
tab~~~
L.) exists, based on their data which showed that
nitrogen uptake is not solely dependent on root volume or root
length, but on carbohydrate supply from the shoot as well.
This integrated plant response was also shown by Rufty et
al (1981)
in
experiments
where
they showed that root
temperature stress was mediated by carbohydrate flux to the
root and nitrogen flux to the shoot. Thornley(1972, 1976),
constructing mechanistic models based on partitioning of two
substrates(carbon and nitrogen) between three compartments
(leaf, stem and root) reached a similar conclusion to Rufty et
al(1978) in that for a plant undergoing steady state growth
the total activities of the shoot and root are always in
constant ratio to one another. This agreed with an earlier
proposal derived empirically by
Davidson(1969a,
1969b).
Mechanistic
models
have
been
further
developed
by
Charles-Edwards(1976) and Reynolds and Thornley(1982).
As
suggested by a number of authors(Clarkson and Gerloff, 1979;
Dhillon, 1978; Horgan and Wareing, 1980;
Prochazka, 1981;
Vaadia and Itai, 1969), the close coordination of the growth
and activities of root and shoot may be mediated through
hormones produced by the root system.
With few exceptions, such as Cooper and Thornley(1976),
Richards(1981) and Richards et al(1979b) most of the plant
material used to test the validity of functional equilibrium
equations
has been confined to IIleafy plants
such as
perennial ryegrass.
This species has a relatively small
number of leaves and lacks stem tissue during the vegetative
stage of growth.
Consequently, Hunt
and
Burnett(1973)
emphasized that the approach based on equation 3.2 is likely
to be valid only for young grass plants or for dicotyledonous
seedlings in which a very high proportion of shoot weight is
in leaves.
ll
18
However, another
relationship has
expressed as
~M
form
of
describing
the
equilibrium
been proposed by Thorn1ey(1972), and may be
= fm~W--------------------3.3
where ~M is the increment in weight of element M and ~W the
increment in total plant dry weight during a time period ~t
with fm a constant. The tomato(Lycopersicon escu1entum L.)
used by Cooper and Thorn1ey(1976), Richards(1981) and Richards
et a1 (1979b) contrasted with perenni a1 ryegrass used by
Hunt(1975) and Hunt and Burnett(1973) in that tomato has a
large proportion of its shoot weight in the stem.
Moreover,
Richards et a1(1979b) concluded that, even with the fruiting
tomato plants, the functional relationship, as expressed by
equation 3.3, was maintained regardless of ontogenetic drift,
root restriction or a change in growth of the plant from the
vegetative to·the reproductive phase.
The presence of stem tissue may provide another means by
which this equilibrium is maintained other than leaf tissue
alone. The most effective way of arranging the dry matter on
the shoot may be to have the least stem dry weight with the
highest proportion of dry matter allocated to leaf tissue.
Hence, testing the equation 3.2 with "stemmy plants" may be
justifiable even though Hunt and Burnett(1973) acknowledged
that there might be some questions about using equation 3.2
with stemmy plants.
Even though Davidson(1969a, 1969b) did not explicitly
imply the relationship of source-sink proposed 1 ater by
3. 1
is
equation
Warren-Wilson(1972), either
side
of
essentially analogous to
source strength
= source size x source activity--------3.4
That is to say, root and shoot mass may be represented as
source sizes and absorption and photosynthesis as source
activities, so that total activities of shoot and root can be
written as source strengths of shoot and root.
19
It is plausible to imagine that
the
best
plant
performance is achieved when the highest proportion of dry
weight is allocated to the aerial shoot.
However, several
important points should be made. Firstly, the lack of dry
weight allocation to the root must not hinder the survival of
the root system as the function of the root in providing water
and mineral nutrients is vital for further growth of the whole
plant. Secondly, plants rarely grow in a uniformly favourable
environment throughout their growth period, and will at times
allocate more dry weight to the root system at the expense of
shoot growth such as observed in acid sOils(Pinkerton and
Simpson, 1981).
Thirdly, as discussed earlier, interactions
between shoot and root are much more complex than hitherto
thought(Russell,
1977).
However,
having accepted that
shoot/root mass ratio is influenced by various environmental
stresses, it appears that dry weight by itself provides little
information about the adjustment of morphological structures
of the various organs of the plant. The increase or decrease
in dry weight of shoot and root is ultimately related to the
increase or decrease in leaf area, leaf number, root length
and root number.
Studies on the effect of various root
environments on the root morphology have shown that the root
system is capable of compensating for nutrient deficiency in
some parts of the root zone by producing more laterals in
those zones where abundant nutrient is available(Drew, 1976;
Drew and Saker, 1975, 1978; Hackett, 1968, 1972), inferring a
coordination in the root system(Brouwer, 1981). Russell(1977)
refers to this as IIcompensatory growth
Generally, high root
temperature induces a well branched root system(Cooper, 1973;
Nielsen, 1974).
Maize(I~ ~ L.) which is considered to
require relatively high root temperature for satisfactory
growth was more branched at 33 C than 23 C(Atkin et al, 1973).
Garwood(1968) showed that branching of perennial ryegrass was
increased by high temperature and the number of new roots
formed at the base of tillers of grasses and white clover was
decreased.
Mechanical impedance(resistance of soil) can have
a detrimental effect by limiting root growth.
Proliferation
of the root system of corn measured in terms of root length
shows a marked reduction whereas root diameter increases(Veen,
1982;
Veen and Voone, 1981) in response to mechanical
ll
•
l
l
20
impedance. Hallmark and Barber(1981) found that decreased
root growth and lower root surface area per unit of shoot
weight was responsible for the poor
shoot
growth
of
soybean(~llfi~ max(L.) Merrill) grown in soils with high bulk
densities.
While the importance of root morphology influenced by
various environmental stresses has been acknowledged by many
authors, the consequences of differential root morphology on
shoot
morphology have
been largely ignored;
the only
measurement being shoot dry weight after the application of
localized nutrient supply(Drew, 1975, 1976; Philipson and
Coutts, 1977). The importance of leaves as a population of
modules was emphasized by Bazzaz and Harper(1977) when they
concluded that liThe leaf area of a plant is the product of the
number of its leaves and their area. Although the area per
leaf varies with the time at which leaves are initiated, by
far the major contributor to determining the total leaf area
. of Li num is 1eaf number
The argument is that di fferent
shoot morphology has so far largely been studied in terms of
total leaf area and dry weight and the interaction between
shoot and root morphology has not been thoroughly investigated
even though the inter-dependence of shoot and root activities
is becoming clearer.
Hence measurement of shoot dry weight
only in response to differential root morphology seems to be a
limited basis for understanding plant adaptation. Although
the possible significance of morphological
relationships
between shoot and root has been acknowledged by Evans(1972),
the
measurement
of
lIabsorbing
surface
ratio(root
length/photosynthetic area)", which is a measure of the
relative expansion of the two
absorbing
systems,
was
comprehensively used by Hegarty(1973). Even though the work
was only concerned with seedling growth, it appears that the
approach was very sound in that the importance of surface area
ratio in response to nutritional stress was
described.
Richards
and
Rowe(1977a, ~ 1977b)
also
showed that a
relationship exists between the morphological characteristics
of plant roots and shoots and suggested that they should be
taken
into
account
when
considering
the
functional
relationships of roots and shoots as they relate to total
ll
•
21
under
the
particular
plant growth.
They showed that
nutritional conditions of their experiment root length and
leaf area were related and linked in some way through their
common involvement in water and nutrient uptake. Root number
and leaf number were also related through their common
involvement
in
differentiation
processes.
This common
involvement of morphological relationship between shoot and
root was included in the equation proposed by Chung et
al (1982) (see Appendix 6). They suggested that activities of
shoot
and root may be adjusted by including different
morphological characteristics in the equation 3.2, which
eventually gives the following equation,
total plant weight/(leaf number/leaf area)
total IIk"/(root
number/root length)----------------------------3.5
(l
(units used in the present studies are g/(no./cm 2 ) and
g/(no./cm), respectively)
where "k
represents the total contents of
ion(s)
or
compound(s).
They showed that by using equation 3.3 two line
relationships were obtained, which may
have
biological
significance in that cucumber plants adapt to nutritional
stress by increasing root length relative to their leaf area
and decrease their calcium and potassium uptake relative to
their total dry weight. But this implies the non-existence of
a single line functional relationship. Treating data by using
equation 3.5 produced a single line relationship.
The
significance of equation 3.5 is that the organization of root
and shoot systems is closely coordinated and that root and
shoot
morphology
will
show different activities as a
consequence. Hackett(1968) and Drew(1975, 1976) showed the
morphological responses of root systems to nutritional stress
and discussed the significance of differential morphology in
terms of number of root branches. By the same principle,
there is no reason why different shoot morphology should not
affect the activity of the shoot. Although equation 3.5 is
highly empirical, it implies the complex involvement of
morphological features of shoot and root in adaptation to
stress through possible feedback mechanisms. The weakness of
equation 3.2 as pointed out by Hunt and Burnett (1973) is in
the use of dry weight of root as an index of functional size.
II
22
This problem seems to have been partly overcome by using
morphological characteristics instead of root dry weight in
equation 3.5.
It is recognized that the use of root dry weight as a
measure of the functional size of the root system i s not
a 1way s appropri ate.
root
Veen(1977) suggested that the
surface i s often a better functional measure of size than root
volume or root weight when describing plant responses to
nitrate ions.
The increase in ion uptake efficiency which
occurred when plants were transferred from high to low-salt
status (Cram and Laties, 1971) indicates that neither the root
surface nor the root volume or root weight was the limiting
factor.
Lee(1982), using barley(Hordeum vulgare L.) plants,
showed that the pre-nutritional history of a plant had a
profound effect on its subsequent capacity to absorb ions such
as phosphorus, sulphur, chlorine and nitrogen.
This again
implies that root morphology alone may not be the best
measurement of functional size.
Washing excised or intact
primary roots of corn for two hours in distilled water or
diluted nutrient solution doubled the rate of accumulation of
various ions and solutes(Leonard and Hanson, 1972). The
existing content of the ions in the plant appears to play a
significant
role
in
the absorption of ions.
Further
complications come from the fact that the physiological
condition of the plant may affect the absorption efficiency of
the root system(Nye and Tinker, 1969). This demand concept of
the plant in terms of source-sink relationships will be fully
exploited in the next Chapter. In summary, the physiological
condition
of the plant, nutrient availability and root
morphology may influence the activity of the root in an
integrated manner, which may explain why· equation 3.5 which
includes shoot and root morphological terms other than dry
weight describes the adaptive response better than previous
equations(Chung et al, 1982).
The conflict between Hunt(1976, 1977) and Thornley(1975,
1977) over the way of expressing the functional equilibrium
between shoot and root as shown in equations 3.2 and 3.3
represents the typical argument between an empirical and
mechanistic modeller in the field of plant
physiology.
Thornley(1977) argued that "Hunt's method almost amounts to
plotting numbers against themselves, a procedure guaranteed to
produce a linear relationship" and showed the mathematical
calculation by which it is possible to draw equation 3.2 out
of equation 3.3.
The point is that Hunt(1976} chose to
emphasize the biological significance of equation 3.2 rather
than
preclslon
of
the
relationship
itself,
whereas
Thornley(for example, 1976} placed more emphasis on the
analogy of a plant as a system with various parts or organs
working together in a way analogous to a machine.
Hunt(1981}
defended his empirical model by stating that lithe real ity of
growth is submerged by careless or unlucky experimentation or
by the natural variability or inaccessibility of the subject
material". Ignoring the relative arguments supporting each
point of view, functional equilibrium relationships have been
demonstrated whichever equation is used(Richards, 1977}.
Since the concept of USR and SAR, representing the
efficiency of shoot dry weight as a producer of total dry
matter and efficiency of root dry weight in absorbing nutrient
and water respectively, are the major part of the functional
equilibrium equation 3.2, it is desirable to describe these
parameters. USR is defined as total plant weight per unit dry
weight of shoot per unit time.
As was shown by Hunt and
Burnett(1973} and adapted by Troughton(1977}, USR is a similar
concept to Unit Leaf Rate(ULR=Net Assimilation Rate}. SAR is
defined as total mineral content in the plant per unit dry
weight of root per unit time(Hunt, 1973}.
In Section 2 of this Chapter, equations 3.2 and 3.3 will
be used to test whether equilibrium relationships between
shoot and root of cucumber plants treated with various
environmental stresses, as set out in Chapter 2, do exist.
Although ThornleY(1977} argues that the same quantities were
multiplied to both sides of equation 3.3 to produce equation
3.2, they will be viewed as different equations. Another form
of functional equilibrium relationship shown in equation 3.5
will also be tested. None of the literature concerning the
functional equilibrium relationship examined the different
equations using the same elements, and it seems useful to show
the relationship with all the individual elements concerned as
24
well as with different equations. However, for the sake of
brevity only the data from Expts. 2 and 6 will be used for
comparing the total sum of element as well as the individual
element.
For Expts. 3, 4 and 5 only the sum of the elements
will be used.
But unless described, the
trends
with
individual elements were not necessarily different from the
sum of measured elements. Experiment 3 in which the content
of potassium and calcium in the root was not analysed will be
shown with the reasonable assumption that total amount of
those elements in the roots are small relative to the rest of
the plant. In Section 2, solution depth and volume treatments
in Expts.
3 and 4 were excluded from the symbols for the
clarity of the figures.
shoot/root
ratio
contain
Since the USR, SAR and
biologically meaningful concepts and they are the components
of equation 3.2, detailed analysis of these components will be
shown in the Section 3. Data from Expt. 1have. been excluded
in plotting the equations since the analysis of mineral
elements was not performed.
Expt.
3 was excluded from
Section 2 since it was considered that Expt.
2 provided
enough information to describe solution temperature effects.
Volume treatments in Expt.
4 were also excluded in the
results of Section 3.3-3.5 for the clarity of the figures.
The other plant responses that are worth considering when
discussing the functional equilibrium relationship between
shoot and root are the root morphology and the leaf and stem
weight ratios.
It is postulated that the use of root dry
weight alone is not sufficient to represent the root response
influenced
by
various
environmental
stresses.
Root
morphological response with the ratio of root number/root
length(number per cm) is shown in Section 4 for Expts. 1, 2,
5 and 6. The proposition that Hunt and Burnett(1973) made
with respect to the use of equation 3.2 was that there would
be little value in using the equation with stemmy, aged
plants.
Since the cucumber plant has a high proportion of
stem in the total shoot weight, it is considered important to
look at the shoot response in terms of structural arrangement
between leaf and stem weight. Stem weight ratios(SWR, stem
weight/plant weight) and leaf weight ratios(LWR, leaf weight/
plant weight) are shown in Section 5 for all the experiments
performed.
Part of hypothesis in the equation 3.5 was
that there exists a close relationship between leaf area and
root length, and root number and leaf number as suggested by
Chung et al (1982) and Richards and Rowe(1977a, 1977b).
This
relationship is shown in Section 3.6 with the Expts. 2, 5 and
6. It was considered that solution temperature and different
levels of nitrogen and calcium in the solution would represent
the root environments, and light
intensity
for
shoot
environment to show such relationships between shoot and root
in the series of experiments reported in this thesis.
With
the exception of Expts. 3 and 4, all the ratio terms shown in
this Chapter are presented in the form of a smooth curve,
derived from the Richards(1959) function, described in the
Chapter 2.
26
3.2.
Results using the functional equilibrium equations
The results of Expt. 2 based on equation 3.2 are shown
in
Figs.
3.1-3.4 for potassium, calcium and nitrogen
considered separately, and the sum of the three elements.
It
is clear that two line relationships exist based on the
different solution temperatures applied, with the exception of
potassium(Fig.
3.1) due to the large confidence limit of the
slopes.
The high solution temperature treatment
showed
consistently
greater
slopes
in all elements measured.
However, the low solution temperature treatment resulted in
the particularly poor relationship between the mass ratio and
the 1/activity ratio with
the
exception
of
nitrogen
uptake(r=O.935).
• 18
I
T
-.,.--
r--,...----r---,
+
.16
+
+
+
+
.14
(.!)
......
+
(.!)
.12
....
t0
*
a:
a:::
...
l-
0
0
::x::
~
I-
•
III-
.138
a:::
• :11
.136
+
./
...
o -
0
+
+
...
-1-
.
• •
+
..
+
+
+
E9
+
+
...
..
...
...
.134
.02 ~I--~--~--~--~~--~--~--~--~--~--~--~--~--~--~--~~--~--~--~--~--~
2.8
1.2
1.4
1.6
1.8
2.13
2.2
2.4
2.6
3.10
3.2
l/ACTIVITY RATIO WITH RESPECT TO K (G/G/OAY) I (G/G/OAY)
Fig.
3.1.
The effect of different solution temperatures on the
relatlonship between the mass ratio and the reciprocal of
activity ratio with respect to potassium uptake.
*;12.5'C
+;32.5'C.
Slope and confidence liwit for low a9d high
temperature treatments are; O.OJ43±O.UJO, O.U614±O.O~
\$, excluded from linear regression)
N
'-J
.18
+
.16
+
+
-
+
+
.14
c..:l
"
ED
c..:l
.12
+
o
......
*
t-
~
.H'l
t-
o
o
:c
~ .08
.
t-
o
o
n:::
.06
*
.04
.02~'
1.8
2.0
2.2
2.1
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
1.1
1.6
1.2 ~~~~~~~~~~~~~~~~~~~~~~J
l/ACTIVITY RATIO WITH RESPECT TO CA
Fig.
(G/G/OAYI/(G/G/OAY)
3.2.
The effect of different solution temperatures on the
relationship between the mass ratio and the reciprocal of
act ivity ratio with respect to calcium uptake.
*;12.5'C
+; 3 2.5'C.
Slope and confidence limit for low anu high
temperature treatments are; O.0156±O.014, O.0551±O.014
($, excluded from linear regression)
N
CD
.18rr--'-'-~--'--'--r--'~r-~-'--'-~--~-'--~-~-'~~~---
+
.16
.14
,....
(,!)
.......
(,!)
0
.....
.....
0:
Ck::
.....
0
.12
.10
0
:c
~ .08
.....
0
0
0::
.06
~
• 04
.02
...
I
1.4
1.6
1.8
I
1
2.0
2.2
2.4
lIACTI VITY RAT! 0 WrTH RESPECT TO N
Fig.
3.3.
2.6
2.8
3.0
(G/G/DAY1/(G/G/OAY)
3.2
The effect of different solution temperatures on the
relationship between the mass ratio and the reciprocal of
activi~Y ratio with
respect. to nitrogen uptake.
*~12.~'C
+;3Z.~~.
Slope and confldence llmlt for low ana hlgh
temperature treatmeQts are; O.0120tO.0085, O.0544±O.0044
($, excluded from Ilnear regresslon)
3.4
N
ill
.181-
--r--r---,---.------,~--.--r-_:+~--r--~~-1--,--:J
.16
+
1
.14
t.:)
ED
't.:)
.12
e
......
~ .10
:#=
0::
l-
e
e
:c
(J') .08
"-
I-
o
o
a:::
.06
j
.04
1
.02
I~----~--~~----~--~~--~~--~~--~~--~~--~~--~~--~~--~~--~~--~
.4
.5
.6
.7
.8
l/ACTIVITY RATIO WITH RESPECT TO SUM OF K. CR AND N
Fig.
3.4.
.9
loB
(G/G/OAY) I (G/G/DAYl
The effect of different solution temperatures on the
relationship between the mass ratio and the reciprocal of
a~tivity ratio witQ.resQ~ct to su~ of potassium,
calcium and
nltrogen uptake.
,12.~ C +;32.5 C.
Slope and confidence limit for low and high temRerature
treatments ar~;
O.119±O.057, O.201±O.038 (®, exclu~ed from
1,near regresslon)
1.1
w
o
The relationships based on equation 3.3 are shown for
Expt.
2 in Figs. 3.5-3.8 for potassium, calcium, nitrogen
separately and the sum of the ions, respectively. The initial
values of plant dry weight / and of individual elements and
their sum have been put equal to zero whenever equation 3.3 is
used.
Points near to the origin on the figures due to the
poor plant growth resulting from low-solution temperature are
shown on the separate acetate overlays. It is clear that
results obtained from equation 3.3 showed a single line
relationship with all the elements when equation 3.2 showed
two line relationships(Figs.
3.1-3.4).
The
correlation
coefficient with all the elements concerned was better than
0.99. Equation 3.3 markedly improved the relationship with
the potassium data(Fig. 3.5) compared with that obtained with
equation 3.2(Fig. 3.1). A relationship with respect to sum
of the elements(Fig. 3.8) was not different from the results
obtained for individual elementS(Figs. 3.5-3.7).
+
+ +
•
+
* *
+
.,I;
**
*
~~~~--~~~--~~~~~~-L~~s
S
+
110
120
I
j;
+
G 100 .
t-
::r:
'-'
.......
IJ.J
80
3:
>0::
Cl
zt-
60
a:
...J
0-
10
20
o ...,-4-
o
1
2
3
1
5
6
7
8
TOTAL K CONTENT (Gl
Fig.
3.5.
The effect of different· solution temperatures on the
relationship between pl~nt dry weight and total Qotassium
content. *;12.~ C +;32.5 C. Y=18.40X-O.628; r=O.99' (Points
near to the origin are shown on the acetate overlay)
(.0
1')
,....-,....-...--.. . .------.---r'~--.--..,.....-.------.----- ~
+
+
+
+
+
•
*
*
*
•
*#
~~--~--~~--~--~-4---L--L-~
___ L_ _L_~__~s
~
14~
12~
G
u,~
I-
:r:
C,!)
.....
L1J
3:
6~
>-
0:::
C
I-
z
6~
5
I:L.
4~
2~
'\~
1
2
3
5
4
6
6
9
TOTAL CA CONTENT (G)
Fig.
3.6.
The
effect of different solution temperatures on the
relatlonship be~ween plant dry weiQht and total 9 al cium
content.
;12.5 C +;32.5 C. Y=16.98XfO.290; r=O.997 lPoints
near to the origin are shown on the acetate overlay) .
I
w
w
.
r--r--r--r--~~--~~--.-~--'-~--~~~-~
+
+
+
•
+
•
•
•,
• ••
•
~~~--~~~~L-~~~~~~~L-~~s
S
+
140
120
G 100
-
t::t:
C)
..... 60
UJ
::s::
>~
c
~
60
a:
.-J
Q..
40
20
0
0
1
Fig.
2
3
4
5
6
TOTAL N CONTENT (G)
3.7. lThe effect of diff~rent dsolutionh temp~ratures on the
re atlonshlP between P 9nt
ry welg t ahd total nltrogen
content.
;12.~ C +;32.
C. Y=20.62X-O.269; r=O.999 ~Points
near to the origin are shown on the acetate overlay)
7
w
+:>
+
+
+
+
+
*
*
*
*
*
+
*
"
* **
**
**
*
140
120
B 100
I-
:J:
(!)
UJ
~
80
>0::
C
I-
z
a:
60
-I
Q..
40
20
00
4
2
6
8
10
TOTRL SUM- OF K. CR AND N CONTENT (G)
Fig.
3.8.
The effect of different solution temperatures on the
relatiQnship b~tween plant dry weight ~nd2 t9tal SU m ,Qf
;1.5 C +;3Z. 5 C.
QotaSSlum calclum aad Oltrpgen content.
Y=6.ZU3X-O.Zo5;
r= .9YY (polnts near to the origin are shown
on the acetate overlay)
w
U1
36
in
which
The relationships based on equation 3.5
morphological aspects of shoot and root are expressed in the
form of leaf number/leaf area and root number/root length are
shown in Figs. 3.9-3.12. Both initial values have been put
equal to zero whenever equation 3.5 is used. Points near to
the origin on the figures are shown on the separate acetate
overlays. For potassium, the inclusion of the morphological
ratios in the equation 3.3 did not make any difference to the
correlation coefficient(Fig. 3.9), compared to Fig.
3.5.
Using equation 3.5 with calcium (Fig. 3.10), nitrogen(Fig.
3.11) and the sum of the three elements(Fig.
3.12) did not
improve
the correlation coefficients.
In short, it is
considered that outcome based on equation 3.5 does not show
any differences from equation 3.3 even though morphological
terms are included.
+
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
o~~~~-L~~~~L-~~-L-L~~~~i-~-L~~s
o
~
s
10
3
xll
+
.....
'"~ HJ
u
.
"0
z
9
"C)
,....,
8
a:
UJ
~
a:
7
IJ..
a:
UJ
.
...J
6
"0
z
5
IJ..
a:
UJ
..... 4
...J
"-
I-
X
C)
3
UJ
3:
>~
2
!
1
c
0
2
0
4
6
8
10
TOTAL K CONTENT/fROOT NO./ROOT LENGTH)
Fig.
3.9.
12
14
16
(G/(NO./CM))
The effect of different solution temperatures on the
relationship between plant dry/!eight/(leaf n~mber/leaf areh1)
and total Qot?sslum
content root
num ber/root
lengt •
*;12.5'C +;32.5 C. Y=599.6X-70. 2; r=O.975. (Points near 0
tne origin are shown on the-acetate overlay)
W
"-J
+
+
*
*
*
*
*
+
•
I
* *
•
*
* *
•
*
3
10 Xll
of
....
N
~ 10
.......
0
.
z
.......
9
(.!)
....
ffi
8
~
u..
7
UJ
...J
6
a::
.......
0
•
z
5
u..
ffi
..... 4
...J
.......
I-
:r:
C)
....
3
UJ
X
>0:::
2
I-
1
C
~
lC
0fa
2
4
6
8
10
12
TOTAL CA CONTENT/tROOT NO./ROOT LENGTH)
Fig.
14
16
(GI (NO. /CM) )
18
3.10. The effect of different solution temperatures on the
relationship between plant dry wei ht/(leaf number/leaf area)
a~d2total cal~ium CQntent/~root_BuID er/r 0 9t length).
*;12.5 'C
+,3 .b c.
Y-bbl.YX-34.21,
r-.Y~.
~Polnts
near to t he
origin are shown on the acetate overlay)
9
2fa
w
OJ
+
*
*
*
*
*
*
•
*
*
* *
*
*
~~~~~~-L-L~~~~L-~~~-L~~~~L-~~
~
¥1
~
3
10 Xli
To
--is 10
N
.
......
0
z..., 9
......
C)
--
ffi
8
~
u..
7
LLJ
...J
6
0
5
a:
.
......
z
u..
ffi
...J
...,
......
4
~
:J:
C)
3
UJ
:x
>n::::
c
~
~
2
1
...J
Q..
00
2
468
TOTAL N CONTENT/fROOT NO./ROOT LENGTH)
Fig.
10
12
14
(G/(NO./CM))
3.11. ,The effect of different solutio~ temperatures on the
redlationship between plant dry/!eight/(leaf n~mber/leQf arel)
an
total
nltrogen
content root
number/root
length.
*~12.5'C +;32.5'C.
Y=677.3X-63. 5; r=O.980. (Points near 0
tne origin are shown on the acetate overlay)
W
1.0
-,
r--r---r-r--r-.,.----,-.. . . . .~--
+
*
*
*
*
+
*
*
•
*
*
* *
*
*
(J)
10 3 x11
+
.-N
L
u
.
10
........
a
z
/
9
........
<..!)
8
a:
UJ
a::::
a:
+
7
!J..
a:
UJ
-'
........
0
.
Z
6
+
S
j
+
lL..
a:
UJ
-'
4
+
........
~
::c
t.:)
.-.
UJ
3:
3
I-
/+
>a::::
Cl
~
z
a:
-'
0-
S0
Fig.
3.12. The effect of different SOlutio
temperatures on the
relationship between p13nt dry weight/ leQf number/ leaf ~rea)
and total sum of pot~sslum, calclum an b nltrogen content/ root
number/root
length).
*·12.5'C +;32.5'C.
Y=203.31X- 0.8;
r=0.979.
{Points near to ihe origin are shown on the acetate
overlay)
.p,
o
41
In Expt. 3, plants were grown at different solution
temperatures and at different solution depths, and the results
of this experiment, using equations 3.2, 3.3 and 3.5 are shown
in Figs. 3.13-3.15. The outcome on the relationship between
mass ratio and the reciprocal of the activity ratio(equation
3.2) with respect to the sum of potassium and calcium is shown
in Fig. 3.13. The relationship varied with temperature of
solution, with a significant difference in slope of line being
observed between high(22.5 and 32.5 C)
and
low(12.5 C)
solution temperatures. Because different slopes of the lines
were produced under root restriction, resulting from shallow
solution depth(5mm), the percentage of potassium in the plants
was examined, and results are shown in Tables 3.1 and 3.2 for
Expts.
2 and 3, respectively.
Average dry weight of the
plants is also shown in Table 3.1 for reference to show the
differences
obtained
from
high(32.5 C) and low(12.5 C)
solution temperature treatments. It is clear that while the
percentage
of
potassium in both temperature treatments
remained relatively constant in the case where no root
restriction occurred in Expt.
2(Table 3.1), there was a
3 with
marked decline in the potassium per centage in Expt.
high temperature treatments(Table 3.2.) while it remained
stable with low temperature treatment.
The same data are
plotted again using the equation 3.3, which is shown in Fig.
3.14. Apart from the clustered pOints resulting from poor
plant growth, equation 3.3 produced a good relationship
represented by single line. As was found in Expt.
2, the
inclusion of morphological terms in equation 3.3 did not
improve the correlation coef.ficient(Fig. 3.15).
I
I
I
I
.21
.22
I-
.20
I
--+
.18
~
.16
~
"'j
~
/'"
+*
o .14
,
+
I-f
*
/
-
...L.
+
•
+++
~
+
+'
~
-----
j
I
+
+
+
+
I-
0:
et::
.12
I-
..
0
~ .10 ~
•
..1- .... ,
+
I-
oC) .08
et::
. 06
.04
I
•
/'"
**/.~
* ~
~
*
7
1/RCTIVITY RATIO WITH RESPECT TO SUM OF K AND CR (G/G/OAY)/(G/G/ORY)
Fig.
3.13. The effect of different solution temperatures and depths on
the relationship' between the mass ratio and the reciprocal of
activity ratio with respect to sum of potassium and calcium
uptake in the shoot • • ~32.5'C +;22.5'C *;12.5'C. Slope and
confidence limit for 12.~'C, and 22.5'C plus 32.5'C are;
O.0636±O.0129, O,0158±O.0024. (Depth treatments were excludea
from the symbols)
8
..j:::>
N
240
+
220
+
+
200
160
lLJ
Cl
z
a:
-1
Q..
+
/'
/
......
f-
+
:///
f-
[5 140
3:
/+
+
(..!)
>a:::
+
+
+
180
+
120
100
+
80
.+
++
60
/.
+.
+
+
+
+..:+ + +
40
j
20
0
L ___
0
1
2
3
4
5
6
7
TOTAL SUM OF K AND CA
Fig.
8
9
10
l ___11 Ii
L __
12
(G)
3.14. The effect of different solution temperatures and depths on
the relatlonship between plant dry weight and total sum of
~otassium and calcium uDt~ke in the shoot.
.~32.5'C
+j22.5'C
;lL.~'C.
Y=LL.40X-l./l;
r=O.886.
tDeptn treatmenLs were
excluded from the symbols
+::>
w
10
3
It
110
,....,.
~
~
u
"-
0
.
:z
100
+
90
+
80
0
.
+
+
50
u..
a:
UJ
-'
40
/
+.
"t.:)
.......
+ .
30
UJ
20
:z
a:
-'
a..
+
+
+
0
I-
+
.
*+
3:
>a:::
/..
+
:z
II
~
70
60
/
+
+
+
a:
a:
u..
a:
UJ
-'
"-
+
+
"~
UJ
0::
+
10
0
2
0
4
6
8
10
12
TOTAL SUM OF K AND CA/(ROOT NO./ROOT LENGTH)
Fig.
14
16
18
(G/(NO./CM))
3.15. The effect of different solution temperatures and depths on
the relationship between plant dry weight/(leaf number/leaf
area~ and the total
sum of potasslum and calcium in the
shoo I(root number/r8ot length) • • ~32.5'C +;22.5'C *;12.5'C.
Y=bZ 5.6X-3088.6~ r= .892.
lDepth Lreatments were excluded
from the symbols}
.p,.
.p,.
45
Table 3.1.
Potassium percentage(±s.e.) of leaves treated
at
different solution temperatures(Expt. 2). (Average
plant dry weight(g) is shown for reference)
days
temp
%
dry wt
days
temp
%
dry wt
14
7
32.5 C
12.5 C
5.90±1.95 3.95±0.40
2.50
0.81
21
32.5 1 C
12.5 1 C
6.09±0.25 5.31±O.32
39.5
1.94
1
1
32.5 1 C
12.5 1 C
6.76±O.01 4.75±O.05
11.3
1.54
28
32.5 1 C
12.5 1 C
5.50±O.39 6.13±1.02
119.9
3.35
46
Table 3.2.
days
Potassium percentage of leaves(±s.e.) treated
at
different solution temperatures
and depths(Expt. 3)
21
temp-------32~SiC--------------22~SiC--------------i2~SiC-------
depth
5mm
50mm
5mm
50mm
5mm
50mm
% 4.99±O.24 4.91±O.07 4.44±O.52 4.73±O.42 2.75±O.26 3.54±O.34
---------------------------------------------------------------days
42
---------------------------------------------------------------1
temp
32.5 C
22.5 1 C
12.5 1 C
depth
5mm
50mm
5mm
50mm
5mm
50mm
% 2.93±O.19 2.69±O.33 2.90±O.20 2.88±O.47 2.32±O.44 3.37±O.84
---------------------------------------------------------------days
63
1
12.5 C
temp
32.5 C
22.5 1 C
5mm
50mm
5mm
50mm
5mm
50mm
depth
% 1.88±O.21 1.52±O.13 1.08±O.32 1.28±O.09 4.29±O.42 3.91±O.45
1
47
The experimental results from Expt. 4 are shown in Figs.
3.16-3.18 with respect to the sum of potassium and calcium.
Equation 3.2 produced an acceptable linear relationship when
different
ionic
strengths
were
imposed(Fig.
3.16),
particularly compared with data shown in Figs. 3.4 and 3.13.
Equation 3.3 produced a good linear relationship(Fig. 3.17),
but close inspection of the clustered data indicates the
probability of two lines, based on the different ionic
strengths of solution. The slopes were 12.71 and 28.46 for
full
nutrition,
and
5%
plus
2% strength treatment,
respectively. The correlation coefficient obtained from using
equation 3.5 indicated a good linear relationship(r=O.97).
The congregation of paints near to the origin in Figs.
3.17
and 3.18 was an inevitable result of the growth pattern of the
plants in the experiment.
·60
.55
f
-.---
...
. 5~
.45
...
a .40
Co.:)
o
...
.35
...
0-4
I-
eI:
0:: • 3~
11<
...
...
0
~
(f)
"'",+
.......
I-
g
.2~
+
... +
.. +.
0::
• 15
.~ ..... +
<I
• 1~
.
. 05
0
'"
.'
+
t
+
...
+
+
+
.25
...
...
I-
...
...
'"
'"
...
+
+
+ +
+
... ...
... +""r:F ...
...
+
2
~
4
6
8
1/RCTIVITY RRTIO WITH RESPECT TO SUM OF K RND CR
Fig.
1~
12
14
(G/G/DRY1/(G/G/DAY)
3.16. The effect of different solution ionic strengths, depths
and volumes on the relationship between the mass ratio and the
reciprocal of activity ratio ~ith respect to sum of potassium
and
calcium uBtake.
.-ful I strength +-5% strength *;2%
strength.
Y=O. 261X+O.0810;
r=O.807.
(Depth ana volume
treatments were excluded from the symbols)
+::>
00
--.-1
'"
.
q<
+
N
+
+
It
+
*
+ +
+
+
+
...
• + +
...
+
•
+
+
+
*
*
*
+
+
+
...
,
... * * *
. ..
•....L.* '+*
*
500
I ~T---'----'
.--.--.---.
450
400
350
(:)
I-
:r:
(:)
300
......
~ 250
>-
et::
Cl
I-
z
200
a:
--'
a...
150
100
50
0
5
0
10
15
2l!J
25
TOTAL SUM OF K AND CA CONTENT
Fig.
30
35
40
(G)
3.17. The effect of different solution ionic strengths, depths
and volumes on the relationship between plant dry weight and
total sum of potassium and calcium content • • ;full strength
+-5% strength *-2% strength.
Siope and confidence limlt for full strength and 5 plus 2%
strength treatments are; 12.71±O.136, 28.46±O.603. (Points
near to the orlgln are shown on the acetate overlay.
Depth
and volume treatments were excluded from the symbols)
+::>
1.0
Iii I
I
.
i I
(D
+
+
+
+
+
+
*
*
'+
+
*
*
+ ,+
•
+
+
*
+
*
++•.
•
*
•
*.
lSI
lSI
lSI
l()
.'
+
*
• 1'. ..
~
,
10
3
X65
~
L
U
,/
60
"-
0
. 55
z
~
50
a:
45
UJ
~
a:
40
/
IJ..
a:
~ 35
.
"-
~ 30
IJ..
a:
UJ
-I
"....
:r:
t!)
25
20
~
~
>-
~
15
10
t-
Z
a:
-I
5
0-
0
10
0
20
30
40
TOTAL SUM OF K AND CHI (ROOT NO. fROOT LENGTH)
Fig.
50
60
70
(G/ (NO.lCM))
3.18. The effect of different solution ionic strengths, d~pths
and volumes on th~ relationship between plant dry weight/t"leaf
number/I~af
area) and the total sum of
potasslum
and
calcium/troot
number/root
length).
.;full strength +;5%
strength *;2% strength. Y=920.9X-382.0; r=O.973 (Polnts near
to the origin are shown on the acetate overl~y. Depth and
volume treatments were excluded from the symbols)
Ul
<:)
51
The results obtained from equations 3.2, 3.3 and 3.5 are
shown in Figs.
3.19-3.21 when plants were treated with
different
ionic
strengths
of
solution
and
1 i gh t
intensities(Expt.
5).
Equation 3.2 produced a good linear
relationship (r=0.99)(Fig. 3.19). Fig. 3.20 obtained from
using equation 3.3 confirms the previous result(see Fig.
3.17) in that two lines were produced based on different
levels of ionic strength(significant at p<0.05). They did not
occur with different levels of light intensity, which is in
good agreement with the result obtained from the relationship
between root length and leaf area, and root number and leaf
number(see Appendices 1 and 2). The extended line produced
from the low ionic strength solution treatment in Fig.
3.20
was a reflection of the experimental design and plant growth
and is based on a better spread of data pOints, compared to
the situation in Fig. 3.17. It appears that the two lines
produced by equation 3.3 were amalgamated into one line by
using equation 3.5(Fig. 3.21).
.40
r
I
.35
.30
..:
t!)
't!)
/1
/.
....~: .
,....
.25
0
]
~
~
......
I-
~ .20
I-
o
•
t-
•
/
0
:t:
~ .15
e
e
a::
l-
~
.10
.05
°0
.2
.4
.6
.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
3.0
l/ACTIVITY RATIO WITH RESPECT TO SUM OF K. CA AND N (G/G/DAYl/(G/G/DAYl
Fig.
3.19. The effect of different solution ionic strengths and light
lntensities on the relationship' between the mass ratio and the
reciprocal of activity ratio with respect to sum of potassium
and
calcium and nltrogen uQtake.
+;full strength *;5%
strenqth Y=O.117X+O.028; r=O.977 (Light lntensity treatments
were excluded from the symbols)
U1
N
160
"1
j
140
120
~
100
t-
:c
~
......
UJ
:3::
813
>n:::
Cl
I-
z
a:
I
60
/+
~
~
.--l
LL
I
413
...
~
~
20
o
13
2
4
6
8
10
12
14
TOTAL SUM"OF K. CA AND N CONTENT
Fig.
1
(Gl
3.20, The effect of different solution ionic strengths and light
lntensities on the relationship between plant dry weight and
total sum of potassium, calcium and nitrogen content.
+;full
strength *;5% strength.
Slope and confidence limit for full strength, and 5% strength
treatments are;
6.215±0.243 1 8.168±1.03. (Light intenslty
treatments were excluded from ~he
symbols)
Ul
W
103 X12
.-.--.
-.-r-,-r-.--.-r
--.
~
u 11
+
"§E. 10
"
(.!)
./,/
9
//./
,-..
a:
IJJ
0:::
8
a:
u..
a:
+
+
7
~
~
~
IJJ
.
...J
'0
Z
I.L.
a:
6
+
5
~
~
+
IJJ
...J
"
4
+
I-
:c
l:)
......
LLJ
3
3:
>-
2
l-
I
0:::
CI
z
a:
...J
Q...
£3
5
0
10
15
20
25
30
TOTAL SUM OF K, CA AND N/CROOT NO./ROOT LENGTH)
Fig.
35
40
45
50
(G/(NO./CM))
3.21, The effect of different solution ionic strengths and light
lntensities on the relationship between plant dry weight/lleaf
number/leaf area) and total sum of potassium, calcium and
nitrogen content/froot number/root length). +;full strength
*;5% strength. Y= 98.5X-54.69i
r=O.977.
(Light intenslty
treatments were excluded from che symbols)
(J1
+:>
55
The effects of different
levels
of
nitrogen
and
calcium(Expt.
6) on the three equations with respect to
potassium uptake are shown in Figs. 3.22-3.24. When equation
3.2 is used, fitting a linear line through all the points
showed a
tolerable
relationship(Fig.
3.22,
r=0.855).
However, scattered points in full nutrition and low-nitrogen
treatment showed particularly poor relationship, correlation
coefficients being 0.345 and -0.290, respectively. Equation
3.5(Fig. 3.24) showed more scattering of points than equation
3.3(Fig. 3.23). Nevertheless, the fact that the inclusion of
morphological terms in equation 3.3 did not make a great
difference is in good agreement with previous results shown,
especially in Figs. 3.5-3.12. However, relationships in the
case of calcium seem
more complicated. There seem to be
systematic deviations based on treatments in all
three
equations.
Equation 3.2 showed three parallel lines(Fig.
3.25), slope and confidence limit for
full
nutrition,
low-calcium and low nitrogen treatments being 0.0169±0.0017,
0.0161±0.0014 and 0.0167±0.0023, respectively.
The result
obtained from equation 3.3 completely avoided the clustered
points(Fig. 3.26) as occurred in previous results(see Fig.
3.17)
especially
those
of low-calcium treatment.
The
gradients of two lines are significantly different(p<0.05)
with the low-calcium treatment having a higher gradient and
low-nitrogen plus the full nutrition treatments producing one
line. But in the case where equation 3.5 is used(Fig. 3.27),
it becomes a three line relationship, the decreasing gradients
being
in the order of low-calcium, full nutrition and
low-nitrogen treatment, respectively.
The
relationships
obtained from equations 3.2, 3.3 and 3.5 with respect to
nitrogen uptake are shown in Figs.
3.28-3.30, respectively.
A clear grouping of the points according to the treatment
resulted in the case of equation 3.2(Fig.
3.28).
Equation
3.3 produced significantly different slopes, one being low
nitrogen and the other full nutrition plus
low-calcium
treatment(Fig.
3.29). Equation 3.5 produced a single linear
relationship with a high correlation coefficient(Fig.
3.30).
The total sum of the three elements applied to the three
equations showed very similar results to nitrogen alone(Figs.
3.31-3.33).
.50
--.-~
.45
I
*
.40
I
CJ
~
.35
'CJ
a
.30
* ** *
*
*
*
* * *
**
*
*
** * *
**
*
*
I--i
f-
er:
a:::
~-"1
t
.25
*
f-
a
a
Z75 .20
"Ia
~ .15
*
*
*
I
*
~
l
~
j
+ -±t+:
.
l
..,
.10
J
+++.;ftt +-P- * +
+ +
....,I
,-tt
~
j
.05
0
I
1
2
-j
1
*
*
+-++
~l
3
4
5
6
7
8
3
9
1/ACTIVITY RATIO WITH RESPECT TO K (G/G/ORYJ/(G/G/ORYl
Fig.
3.22. The eff~ct of different levels of nitrogen and calcium on
the relatlonship between the mass ratio and the reciprocal of
activity ratio with respect to potassium uptake • • ;full
nutrition +;low-calcium *;low-nitrogen
UI
(j)
r-r-~.--r-r-r~-.-'~r-r-r-r-~.--r-r-r~-'I-.--r-TI-r-r-,-,-,-r-r~-.-'
'T---r-T
I
I
---ro-i
110
~~//~/
+
120
+
C)
//
100
lC)
~
80
>o
0::::
j--
z
+*
//
3:
+
IT
---'
(L
*
10
,~
20
+
+
o
I
I
.5
I
I I I
j
'
+
I
l
./
* *.~ +
.
I I
1.0
~
I
I I
1.5
I I
I
2.0
I I
I
2.5
I
I
I
3.0
TOTAL K CONTENT
Fig.
~
~
#*
01
~
~
~
. /
/+
60
~+
/+
.+
I
/
//
I
I I
3.5
I
I I
Q.0
I
I I
Q.5
I
I
5.0
I
I
I I
5.5
~
J
6.0
(G)
3.23. The effect of different levelds of nitrogen and calcium on
the relatlonshig betweeQ p'lant ry weight. and t~tal potassium
cooteDt.
·~ful·1
nytrltlon
+;low-calclum
;Iow-nltrogen
Y=Z5.Z9X-l.402;
r=O.~75
U1
-.....J
1
10 2x 20
'---'
J
+'
"'"
L
~ 18
~
0
:z:
'-.. 16
~
C)
0::
14
w
a:::
LL
+
+
0::
12
~
0::
---.J
": 10
:z:
0
+
LL
w
8
+.~
.---1
'-..
f-
:r::
l:)
~~
~~+
+
lLJ
0::
+
+
6
+
+
+
3:
1
+
+
>-
a:::
0
f-
:z:
*
2
IT
l
~
q
~'If<*+
., ~ '+t *+
~
j
+
>-i
lLJ
+
+
.---1
D-
0
1
0
2
3
'1
5
TOTAL K CONTENT/(ROOT NO./ROOT LENGTH)
Fig.
6
7
8
9
(G/(NO./CM) )
3.24. The eff~ct of different levels of nitrogen and calcium on
the relatlonship between plant dry weigHt/(leaf number/leaf
area) and total potassium content/froot number/root length).
Y~i~~~~3Q~rO~g~g~ +f18~9r9lcium *; ow-nitrogen
Ul
co
.----,
.50
-----1
-,
j
...j
.45
*
-,
-,
-,
.413
-i
i
..,-i
C)
....,-i
.35
"1
'-
*
C)
...;
-i
.30
-i
cc
n::: .25
,....,
..,
0
>-<
l-
I-
*
0
0
*
i75 • 213
'-
f-
a
~
i
,-i
.15
...,
,113
--i
-,
-;
-l
-,
.135
....I
.J
i
13
2
Fig.
4
6
8
113
12
14
(G/G/ORYl/(G/G/ORYl
16
l/RCTIVITY RRTIO WITH RESPECT TO CR
3.25.
The effect of different levels of nitrogen and calcium on
the relatlonship between the mass ratio and the reciprocal of
activity ratio with respect to calcium
uptake.
.;full
nutrition +ilow-calcium.*;low-lnitroQeo. Slope and confiaence
Ilmlt tor lui I nutrltlon
ow-caTClum
ahd
low-nltrogen
treatments are; O.0169±O.O~17, O.0161±O.do14, O.0167±O.0023
I
18
Ul
\.0
140
120
(,,!)
100
l-
I
(,,!)
......
w
80
3:
~
+
+
;;+
J
>-
a:::
Cl
I-
z
a:
---l
a..
j.p-
/+
60
1J
~
l
20
o
o
~I-L-L~~~~~~~~~J-J-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-L-L-L-L-L~
.5
Fig.
1.0
1.5
2.5
2.0
TOTRL CR CONTENT
3.0
(G)
3.5
4.0
4.5
3.26. The effect of different levels of nitrogen and calcium on
the relationship between plant dry weignt and total calcium
content •• ;full nutrition +;"Iow-calclum ;low-nitrogen. Slope
and confidence limit for low-calcium, and full nutrition plus
low-nltrogen treatments are; 78.81±5.26, 24.24±1.28
5.0
O'l
o
10 3 x20
N
D
.
"-
0
+
18
:z
"- 16
D
a:
w
14
+
++
II::
a: 12
LL
a:
w
+
+
-l
': 10
0
Z
LL
a:
llJ
-l
"-
l-
I
+
8
+
+
++
+
6
D
......
IJ.J
3:
I}
>0:::
0
I-
z
2
*
a:
-l
£L
0
1
0
*
.. *
2
***
'I<
3
I}
TOTAL CA CONTENT/tROOT NO./ROOT LENGTH)
Fig.
5
6
7
(G/(NO./CM))
The effect of different levels of nitrogen and calcium on
the )relationshi P between plan~ dry weignt~(leaf number/leaf
area and total calcium content/~root num5er,root length) •
• ;full nutrition +;low-calcium ·low-nitrogen.
Slope and confidence limit for futl nutrition~ low-calcium and
lQw-nitrogen
treatments are;
1560.9±133.o, 5156.2±780.4,
3.27.
I
621.7±100.6
CJ)
>-'
·50
..
.45
. 10
C)
.35
**
* * **
'-..
C)
.30
......
lcc
a:::
**
.25
I0
0
~
*
*
0
.20
'
*
*
'U.
.
*
*
*
.
* **
* *
t
*
*
*
*
*
*
.........
I-
0
0
a:::
.;:"#+'
.15
.~
/
.10
. 05
0
.
~
,.,:"
.:!-.
0
2
Fig.
1
14
18
16
1/RCTIVITY RRTIO WITH RESPECT TO N (G/G/ORY)/(G/G/ORY)
6
8
10
12
20
3.28. The effect of different levels of nitrogen and calcium on
the relationship between the mass ratio and the reciprocal of
activity ratio with respect to nitrogen uptake.
.;full
nutrition +;low-calcium *;low-nitrogen.
22
m
N
r------r----~r_----_r_._____,_
---,----- -----r-.. ----.-----
140
120
C)
I
I
/0
100 l-
j
/'
I--
:r:
C)
........
w
3:
>-
+
et::
0
I--
z
60
a:
./:
-1
CL
I
40
20
o
I~
__J __ _
o
/
~_ _ _ _L __ _~_ _~_ _ _ _L __ _~_ _~_ _ _ _L __ _~_ _~_ _ _ _L __ _~_ _~_ _ _ _L __ _J __ _~_ _~
234
567
TOTAL N CONTENT (Gl
Fig.
8
3.29. The effect of different levels of nitrogen and calcium on
the relatlonship between plant dry wel~ht and total nitrogen
content • • ;full nutrition +;low-calcium ;low-nitrogen. Slope
and confidence limit for low-nitrogen~ and full nutrition plus
low-calcium treatments are; 62.94±7.~3, 15.45±1.16
9
0'>
W
10 2 x20
N
+
[3 18
"-
0
:z::
"- 16
l.::J
14
IT
n:::
IT
+
+ +
W
12
+
LL
IT
W
....J
LL
IT
+
8'
W
....J
"-
lI
6
+
+
': 10
0
:z::
+ +
+
I
+
+
t.:J
I-i
W
3:
>-
+
4
n:::
0
I-
Z
IT
....J
2
~
Z+
~"'~
...... :- + + + +
0...
0
2
0
4
6
8
10
TOTRL. N CONTENT/(ROOT NO./ROOT LENGTH)
Fig.
12
(GI
14
16
3.30. The effect of different leyels of nitro~e~ and calcium on
the relatlonship between plant dry weignt/(leaf numbe r /l ea f
area) and total nitrogen content/(root number/root length).
.~full nutrition +;low-calcium *;low-nitrogen.
Y=~30.62X-96.11;
r=0.946
18
(NO. ICM) )
..,.
0'>
·50
.45
*
.40
C)
.35
**
'-.
* ** * *
*
* *
*
*
*
*
*** * * * "
** *
*
**
*
C)
.30
0
I-t
t-
o:
n::: .25
t-
o
0
*
*
i75 .20
'-.
t-
~
o
~ .15
~-t
.A
. +.. ~
jj;-tf:
+;1#+ +
.10
.05
0
.5
0
1.0
1.5
2.0
2.5
1fRCTI VITY RRTI 0 WITH RESPECT TO SUM OF K. CR RND N
Fig.
3.0
3.5
1.0
(G/G/DRY) I (G/G/DRY)
3.31. The eff~ct of different levels of nitrogen and calcium on
the relatlonship' between the mass ratio and the reciprocal of
activity ratio with respect to sum of potassium, calcium and
nltrogen uptake • • ;ful I nutrition +;low-calcium *;low-nitrogen
Cl"\
(J1
-------,-
----- J
140
+
120
C)
100
l-
I
C)
.......
w
80
3:
>-
+
n:::
0
rz
a:
/+
60
.....J
0...
10
20
t
*/
~
/
=t
~
r- / -
t-
oI
I
o
Z
4
6
8
10
TOTRL SUM"OF K, CR RND N CONTENT
Fig.
12
14
16
(Gl
3.32. The effect of different levels of nitrogen and calcium on
the relationship between plant dry weight and total sum of
potassium, calcium and nitrogen content.
.;full nutrition
+;low-calcium *;low-nitrogen. Slope and confldence limit for
low-nitrogen and full nutrition plus low-calcium treatments
are; 11.36± l .97, 8.17±1.12
Cj)
Cj)
103X20
I
+
N
D 18
lJ
.
'o
z
'- 16
D
14
~ ~
a:
~
/'
+ +
,/
12
1
-1
': 10
o
~
Z
+
8
~
3:
6
>o
z
+
+
4
'
n:::
I-
+ +
+
t-I
UJ
+
+
-1
:r:
t.:)
~
+
UJ
I..L.
a:
UJ
'-l
..
2
a:
-1
CL
o I,:"",!!",,""
o
2
Fig.
I
T
4
6
8
10
12
14
16
18
20
22
24
26
28
TOTRL SUM OF K. CR RND N/(ROOT NO./ROOT LENGTH) (G/(NO./CM))
3.33. The effect of different levels of nitrogen and calcium on
the )relationshi g between plant dry weig~tL(leaf number/leaf
area
a\d total sum of potassium
calcium and nltrogen
content/ root
number/root
length).
.;full
nutritlon
+;low-ca cium *;low-nitrogen. Y=524.2X-879.7; r=O.944
30
(j)
-......J
00
3.3.
USR, SAR and shoot/root ratio
Overall, the differences in USR values between treatments
were small.
Especially, Expt.
2(Fig.
3.34) and 5(Fig.
3.36) where treatments lasted for 4 weeks did not show clear
trends.
However, Expts.
4(Fig.
3.35) and 6(Fig. 3.37)
where treatments lasted longer showed consistent differences
although marginal. Low solution temperature(12.5 C) generally
induced low values of USR(Fig. 3.34) during the central part
of the experimental period.
Fig. 3.35 in which different
levels of ionic strength, depth and volume(Expt.
4) were
applied showed that the specific shoot activity expressed as
USR increased as nutrient levels in the solution decreased.
The overall trend of USR values when different levels of ionic
strengths and light intensities(Expt.
5)(Fig.
3.36) were
applied showed that different light levels under full strength
of solution treatment did not show differences in USR.
Five
percent of full strength treatment generally induced higher
values of USR except 10% light intensity treatment.
The
values of USR obtained from low-nitrogen treatment(Expt. 6)
showed consistently higher values throughout the experiment
while low-calcium plus full nutrition treatment were almost
indistinguishable(Fig. 3.37). In short, the shape of the
curve and absolute values of USR were similar in all the
experiments performed even though the aerial environments such
as air temperature and light intensity were different, for
example, Expt. 5, the period of November through December of
1981, and Expt. 6 during February through March of 1982.
I
69
0.20
0.15
>,
ttl
"0
........
0)
........
0)
Q)
oj...>
ttl
s....
0.10
oj...>
0
0
~
III
oj...>
'r-
s::
::I
0.05
o
1
2
3
4
time(week)
Fig.
3.34. The effect of different solu~ion temperatures
on the USR.
*;12.5'C +;32.5 C. Fitted valves
derived from Ricbards functlon are plotted wlth
9~~ confldence Ilmlts.
70
+->
o
o
s::
VI
.....
e:
:::l
o
3
6
time(week)
Fig.
3.35.
The effect of different
solution
ionic
strengths, depths and volumes on the USR.
full strength; o;50mm
.;lmm
5~ strengtl1;
Ll.;50mm
A;lmm
270 strength;
o;50mm
.;lmm
{Bars represent tne standard error of mean at each
harvest, Volume treatments were excluded from the
symbols,
9
0.20
71
I,
0.15
>,
ro
-0
-......
en
-......
en
OJ
-l--'
0.10
ro
~
-l--'
0
0
.s::;
Vl
-iJ
......
e:
:::I
0.05
o
1
2
3
4
time(week)
Fig.
3.36.
The effect of different
solution
ionic
strenqths and light jntensities
the USR.
tull strength; o;full llght 0;5 % light [>;10% light
5% strength;
.;full light
_;50% light 4.;10% light
Fitted values derived from Richards function are
plotted with 95% confidence limits.
80
72
0.18
0.12
-I-'
o
o
.s:;
til
.j..)
'r-
;; 0.06
o
1
2
3
4
5
time(week)
Fig.
3.37. The effect of different levels of nitrogen and
calcium on the USR • • ;full nutrition +;low-calcium
*;low-nitrogen.
Fitted
value$
d~rived
from
Rlchards function are plotted wlth 9~% confidence
limits.
73
Progressive curves of SAR with respect to total sums of
measured ions are shown in Figs. 3.38-3.41, respectively.
With the exception of the 1st harvest differences in SAR were
relatively small when plants were treated with different
solution temperatures (Fig.
3.38).
SAR
was
strongly
influenced by solution depth until 6 weeks growth if the lower
ionic strength solution was applied(Fig.
3.39).
The deep
treatment(50mm) showed a higher SAR value than the shallow
treatment(lmm) under the low ionic strength treatment.
In
full strength treatment, however, there was no difference to
the values of SAR in deep and shallow solution. In the given
solution strength, SAR was strongly influenced by light
levels, i.e. the lower the light levels, the higher the
SAR(Fig.
3.40).
Lowering
ionic strength of solution
eventually decreased the values of SAR. However, the values
of SAR obtained from the lowest light intensity with low ionic
strength treatment were higher than full strength treatment
plus full light treatment.
The values of SAR for low
highest
nutrition plus full light treatment showed the
values{Fig. 3.40). There was a clear and significant grading
in the values of SAR where the low nitrogen treatment induced
low values while low-calcium treatment induced a higher values
than control treatment{Fig. 3.41). The order of values of
SAR was the reverse of USR shown in Fig. 3.37.
74
0.24
0.20
>,
tr;;J
"'0
........
en
........
en
QJ
.jJ
tr;;J
~
0.15
c::
0
.~
~
0..
~
0
til
.0
tr;;J
U
or-
4or-
U
QJ
0..
til
0.10
0.05
T
o
Fig.
1
2
3
4
time(week)
3.38. The effect of*~lofferent osolution temperatu res
on the SAK.
,2.~ l
+~jL.~ c.
Fitted values
derived from Richards functlon are plotted with
95% confidence limits.
75
c:
o
+->
0..
S-
o
V>
..0
to
u
'r-
4-
.,....
u
Q)
0..
V>
o
Fig.
3
6
9
time(week)
3.39.
The effect of different
solution
ionic
strengths, depths and volumes on the SAR.
full strength; o,50mm
.;lmm
r,D~
strength;
L\.;50mm
.. ;lmm
o
strength;
o;50mm
.;lmm
ars represent the standard error of mean at each
harvest. Volume treatments were excluded from the
symbols)
~
76
0.5
0.4
>..
10
'"0
.......
O'l
.......
O'l
.........
OJ
+->
0.3
10
l-
I
\
\
e
\
0
\
\
+->
\
0..
I-
\
0
til
.0
10
u
'r-
0.2
4'r-
U
OJ
1
0..
til
\
\
\
T, \
J:" \
""
"
0.1
....
\
\
...... ~ I
~
"e-'
""
,
\
\
-- - ------I
\
\
",
"" "'..T
"
1.......
.....
"..:::- 'I'"
. . . -- ------------1----------------I
o
1
2
3
4
time(week)
Fig.
3.40.
The effect of differ~nt
solution
ionic
strengths and light intensitles on the SAR.
tull strength; o;full light 0;50% light A;lO% light
5% strength; e;full light _;50% light ~;10% light
Fitted values derived from Ricnards function are
plotted with 95% confidence limits.
77
0.20
0.15
>,
to
--0
en
en
OJ
.j..l
to
s....
s::::
0
or.j..l
0.10
0-
s....
0
V)
.D
to
U
4orU
OJ
0V)
0.05
OL-------1L-----~2~----~------~4------~5----
time(week)
F ~ g.
The effect of different levels of nitrogen and
calcium on the SAR. _ifull nutrition +;low-calcium
*;low-nitrogen.
Fitted
values
derived
from
Rlchards function are plotted with 95% confidence
limits.
3.41.
78
The shoot/root ratio obtained from Expts. 1, 2, 4, 5 and
6 are shown in Figs. 3.42-3.46, respectively. Plants grown
in a shallow depth of solution allocated a higher proportion
of dry weight to the root(Fig. 3.42). The sudden decrease in
the shoot/root ratio in the 50mm treatment near the final
harvest date is interesting because it occurred after the root
system filled the tray used to control the solution depth, and
some part of the root started to be exposed to air; a
situation achieved much earlier with the shallow solution
depth treatments.
Lowering solution temperature to 12.5 C
significantly increased the shoot/root ratio(Fig. 3.43). The
higher values were due to the poor root growth rather than
increases in shoot growth.
At low root temperature, root
growth was severely restricted, and was characterized by
greater root numbers relative to its size.
Lowering ionic
strength considerably enhanced the dry weight allocation to
the root(Fig. 3.44). As was found in Fig.
3.42, different
solution depth treatments clearly
influenced the ratio of
shoot/root, especially in the diluted solution treatments.
Lowering light intensities caused an increased proportion of
the dry weight to be allocated to the shoot while low
nutrition
favoured
root
growth(Fig.
3.45), which is
consistent with previous results(Fig.
3.44).
Lowering
nitrogen
level alone in the solution also reduced the
shoot/root ratio while low-calcium level favoured
shoot
growth(Fig. 3.46)
1
79
0.6
0.5
0)
0)
0
+>
ttl
~
+>
0
0.4
0
~
+-'
0
0
.J::
Vl
0.3
0.2
T
o
1
2
3
4
time(week)
Fig.
3.42· Th6 effect of different solution depths on
h
soot
root rat 1o.
~;17 mm
.;50mm .4;5mm o;lmm
Fltted values ger1ved from Richords function
plotted with 9 % confidence 11mlts.
the
are
80
16
12
en
en
0
+-l
<0
~
8
+-l
0
0
~
+J
0
0
.s::::.
<.Il
4
o
Fig.
1
2
3
4
time(week)
3.43. The effect of different solution temperatures
on
the shoot/root ratio.
*;12.5'C +-32.5'C.
Fjtted values derived from Richards functlon are
plotted wlth 95~ confidence limits.
81
9
O"l
O"l
o
+-'
o
o
~
+-'
o
o
.J;;
V1
o
Fig.
3
6
9
time(week)
3.44·
The effect of different
solution
ionic
str~ngths,
depths and volumes on the shoot/root
ratlO.
full strength; o;50mm .;lmm
5% strength; 6;50mm .;lmm
2 % s t re n gt h ; 0; 50mm _; 1 mm
(Bars represent t~e standard error of mean at each
harbvest) Volume treatments were excluded from the
sym ols
82
23
20
Ol
15
........
Ol
0
or-
+>
to
s...
+>
0
0
s...
........
+>
0
0
.s::.
VI
10
5
3
T
o
Fig.
1
2
3
4
time(week)
3.45°
The effect of different
solution
ionic
strengths and light intensities on the shoot/root
ratio.
.
fUo}l strength; o;full light 0;50% light 6;10% light
? to S t r eng t h ; • ~ f u 1 1 1 i g h t • ; 50% 1 i gh t .; 10% 1 i gh t
Fltted values derlved from Richards function are
plotted with 95% confidence limits.
83
15
en
....... 10
en
0
.....,
ttl
~
.....,
0
0
~
.......
.....,
0
0
.t::.
til
5
o
1
2
3
4
5
time(week)
Fig.
3.46. The effect of different levels of nitrogen and
callcium on the shoot/root ratio. .~ f u 1 1 nut r i t ion
+; ow-calcium
*;low-nitrogen.
,itted
values
derived from Richards function are plotted with
95% confidence limits.
84
3.4.
Root number/root length ratio
Measurement of root morphology expressed in terms of root
number per cm of ro~t length treated with different depths of
solution as described in
Chapter 2 showed that shallow
depth of solution enhanced the production of root number
relative to root length(Fig.
3.47).
Shallow depth
of
solution such as 1 and 5mm substantially increased the
production of root number while deep solution treatment(50 and
170mm) showed initially low ratios followed by a gradual
increase. The significant increase in 50mm treatment at 3rd
week coincided with the subsequent decrease in shoot/root
ratio at the final harvest(Fig.
3.42).
Morphological
characteristics of the root system grown under low solution
temperature(12.5 C) were a highly branched root containing
many thick roots and non-extending root initials.
High
solution temperature(32.5 C) treated plants had a distinctive
root morphology which was very fine with fewer non-extending
roots. This can be seen in Fig. 3.48. It was noted that the
number of initials on the root system treated with low
solution temperature may have been underestimated because the
thickness of roots obscured the visibility of root initials on
the underside of the samples observed.
Lowering
light
intensity to 10% natural light intensity induced very poor
root growth relative to shoot growth as shown in Fig.
3.45.
However, the root number/root length ratio showed that it
remained almost unchanged and showed the highest values under
given nutrient strength of solution.
Under natural light
intensity, low nutrient solution strength induced a low value
of root number/root length ratio while the other treatments
did not show a significant difference.
The morphological
characteristics of plants treated with low nitrogen was such
that leaves were small in size and number and showed typical
nitrogen-deficiency symptoms.
The roots were thicker in
diameter, and longer with relatively few branches.
This is
reflected in root number/root length ratio shown in Fig.
3.50. Full nutrition treatment showed high branching compared
to low-calcium treatment.
I
I
85
0.9
-.
E
u
0.8
0
c
.....0
~
ra
~
.s:::
~
c::n
c
(])
0.7
~
0
0
~
~
(])
..0
E
::3
C
~
0
0
0.6
~
0.5
T
o
Fig.
1
2
3
time(week)
3.47. The effect of different ~olution depths on
root number/root length ratln.
.
e;17umm .;5Qmm .;~mm o;lmm
Fltted values derlved from Richards function
plotted with 95% confidence limits.
4
the
are
86
1.2
-.
E
u
1.0
0
s::
0
+.J
It!
~
.s::.
+.J
en
s::
OJ
0.8
+.J
0
0
~
~
OJ
..0
E
::::l
s::
+.J
0
0
~
0.6
0.4
I
o
Fig.
3.48.
1
2
3
time(week)
The effect of diff7rent solution
4
.temp~r~~u5~e
~?32:g~C.ro?~tt~~mb~~,~~~t ~~~~t~dra¥~gm
Rlchards
function are plotted with 95% confidence limits.
87
1.0
E
u
\
\
0.9
\
\
\
\
\
0
\
\
t::
\
0
0 .... \
+->
\
<'C
t::
\
\
..c.
+->
O'l
\
\
~
0.7
Q)
,.....
\
\
\
\
\
-4...l
0
0
\
...
-------_L__ _
~
----------~lJ
~
Q)
.0
E
~
t::
+->
0.5
0
0
~
0.3
T
o
Fig.
1
2
3
4
time(week)
3.49 1
The effect Of different
solution
ionic
sLrengths
and llght intenslties on the root
number/root length ratio.
.
tull strength; o;full light 0;50% light ~;10% llght
5% strength; e;full light _;50% light ... ;10% light
Fitted values derlved from Richards function are
plotted with 95% confidence limits.
88
0.9
E
u
"0.
c
0.8
0
+l
m
~
~
+J
en
c
~
.-+J
0
0
0.6
~
"
~
~
~
E
~
C
+J
0
0
~
0.4
T
0
,
,
,
,
,
1
2
3
4
5
time(week)
Fig.
3.50. Tbe effect of different levels of nitrogen and
calclum on tne root number/root length ratlo •
• ;full nutrition +;low-calcium *·low-nitrogen.
Fitted values d~rived from Richards function are
plotted with 95% confidence limits.
89
3.5.
Stem weight and leaf weight ratios
Stem weight ratios are shown in Figs.
3.51-3.56 for
Expts.
1-6.
Different solution depths did not show clear
trends of dry weight allocation to the stem even though the
170mm treatment had a consistently higher value(Fig. 3.51)
and 5mm treatment the lowest value.
The proportion of the
stem grown in low solution temperature treatment steadily
increased(Fig. 3.52) while SWR values for high temperature
treatment increased sharply reaching the maximum value at
about 3rd harvest. This fact was clarified with the longer
duration of temperature treatment in Expt. 3 (Fig. 3.53).
It is clear from figure that SWR increased in response to low
solution temperature, and that high solution temperatures
lowered values. The effect of different solution strengths,
depths and volumes on the SWR is shown in Fig. 3.54. As was
found in Expt. 1, different solution depth did not induce a
difference in dry weight allocated to the stem at a given
solution strength. La~k of nutrient availability reduced the
SWR.
Values of SWR remained almost unchanged when 10% of
natural light was imposed in both strengths of solution(Fig.
3.55).
At all given light levels, dry weight allocation to
the stem was always higher in high strength of solution
treatment, which agrees with the previous finding(Fig. 3.54).
The effect of different levels of nitrogen and calcium on the
SWR showed that lowering the nitrogen level significantly
reduced the value of SWR while lowering calcium did not show
any difference compared to full nutrition treatment(Fig. 3.56).
The results of LWR from all the experiments performed are
shown
in
Figs.
3.57-3.62.
Different solution depth
treatments failed to produce significant trends in
LWR
although treatments of 50 and 170mm showed consistently higher
values throughout the
experimental
period(Fig.
3.57).
Lowering solution temperature up to 12.5 C induced a gradual
decrease
in
LWR(Fig.
3.58).
High
solution
temperature(32.5 C) treatment showed a different pattern in
which LWR increased sharply followed by sudden decrease,
resulting
in
no differences between different solution
temperatures at the final harvest.
Expt.
3
in
v/hich
1
I
90
0.35
en
'-..
en
0.30
0
'r~
ro
S-
+-l
..c::
en
Q.)
3:
E
0.25
Q.)
~
Vl
0.20
I
o
Fig.
1
2
3
time(week)
3.51. The effect of different solution depths on
stem weight ratio •
• '170mm .;50mm .;5mm o;1mm
Fjtted va1ues ggriVed from Ri~hQras function
plotted wlth 9 % confidence llmlts.
4
the
are
91
0.5
0.4
0'>
0'>
0
4->
(CJ
~
4->
..s::
0'>
0.3
OJ
:=:
E
OJ
4->
VI
0.2
0.1
1
Fig.
2
3
4
time (week)
3.52. The effect of different solution temperatures
on the stem weight ratio.
;12.5'c +;32.5'C.
Fitted values derived from Richards functlon are
plotted with 95% confidence limits.
92
0.6
OJ
OJ
o
.r-
(])
:;:
E
(])
+>
U1
0.2
T
o
Fig.
3
6
9
time(week)
3.53. The effect of different solution temperatures
and depths on the stem welght ratio.
32.5'C; 4;lmm 6.;5mm
22.5:C; .;lmm o;5mm
12.5 C; .;Imm o;5mm
(Bars represent the standard error of mean at each
harvest)
93
o
.~
T
o
3
6
9
time(week)
Fig.
3.54.
The effect of different
solution
ionic
strengths, depths and volumes on the stem weight
ratlO.
full strength; o;50mm .;lmm
5% strength;
A;50mm .;lmm
2% strength;
o;50mm .;lmm
(Bars represent tne standard error of mean at each
~arvest.
Volume treatments were excluded from the
symbols)
94
0.5
0.4
O'l
O 'l
o
0.3
....
0.2
0.1
T
o
Fig.
1
2
3
4
time(week)
3.55.
The effect of different
solution
ionic
strengths and light intensities on the stem weight
ratlo.
full strength; o;full light 0;50% light 6;10% light
5% strength; .;full light _;50% light ,.;10% light
Fitted values derlved from Richards functlon are
plotted with 95% confidence limits.
95
0.5
0.4
en
'-....
en
0
.,....
.j..)
to
~
.j..)
..c.
en
0.3
OJ
:::
E
OJ
+J
til
0.2
0.1
T
o
1
2
3
4
5
time(week)
Fig.
3.56. The effect of different levels of nitrogen and
calcium on the stem weight ratio • • ,i.full nutrition
ritted
values
+;low-calcium
*;low-nltrogen.
derived from Richards function are plotted with
95% confidence limits.
96
0.7
en
"en
0.6
0
~
ro
~
~
~
en
.~
~
3
4-
ro
w
0.5
T
o
Fig.
1
2
3
time(week)
3.57. The effect of different solution depths on
leaf weight ratio •
• '170mm .;50mm .;5mm o'lmm
Fitted values derivea from Richards function
plotted with 95% confidence limits.
4
the
are
97
0.7
en
.......
en
0.6
0
'r-
+-'
<'0
!.~
.s::.
en
'r(l)
3:
4<'0
0.5
(l)
0.4
I
o
Fig.
1
2
3
4
time(week)
3.58. The effect of different solution temperatures
on the leaf weight ratio.
*;12.5'C +;32.5'C.
Fitted values derived from Richaras functlon are
plotted with 95% confidence limits.
98
o
'r-
~
..c:
O'l
'r-
0.3
T
o
Fig.
3
6
9
time(week)
3.59. The effect of djfferent solution temperatures
Qnd gepths on the leaf weight ratio.
32.5 C; .... ;lmm .t.;5mm
22.5:C; .;lmm o;5mm
12.5 C; .;lmm o;5mm
.tSars represent tne standard error of mean at each
narvest)
99
0.7
0'>
0'>
o
'r-
'r-
410
OJ
0.3
I
o
Fig.
3
6
9
time(week)
3.60.
The effect of different
solution
ionic
str~ngths,
depths and volumes on the leaf weight
ratlO.
full strength; o;50mm e;lmm
0% strength;
Ll.;50mm ... ;lmm
2% strength; o;50mm .;lmm
(Bars represent tne standard error of mean at each
harvest. Volume treatments were excluded from the
symbolS)
100
0.8
0.7
en
en
0
~
to
So..
~
0.6
..c
en
Q.J
~
4-
to
Q.J
0.5
0.4
T
o
Fig.
;
2
3
4
time(week)
3.61.
The effect of different
solution
ionic
str~ngths and light intensities on the leaf weight
ratlO.
full strength; o;full light 0;50% light 6;10% light
~%
strength; eifull light _;50% light ",;10% light
Fjtted values derlved from Rjch~rds function are
plotted wlth 95% confidence Ilmlts.
101
0.7
O"l
O"l
0.6
0
"r~
to
~
~
..c
O"l
"r-
a;
3:
4to
0.5
a;
0·4
T
o
Fig.
1
,
I
2
3
4
5
time(week)
3.62. lTbe effect of different levels of nitrogen and
ca Clum on the leaf weight ratio. e,;.full nutrition
+;low-calcium
*;low-nltrogen.
ritted
values
der%ived .from Ricbards function are plotted with
900 confldence llmlts.
102
experimental duration was longer than Expt. 2 showed that LWR
was reduced when low temperature was applied compared to high
temperature.
The effect of different ionic strengths, depths
and volumes on the LWR indicated that low strength treatment
had considerably higher values than full strength with the
exception of first harvest(Fig. 3.60). Generally, different
solution qepths did not produce different values of LWR in a
given solution strength. Plants grown under 10% natural light
intensity showed that LWR remained constant(Fig. 3.61) as was
in the case of SWR(Fig. 3.55). In 5% strength of solution
treatment, full light treatment showed the lowest value of LWR
with the exception of 1st harvest.
In full strength of
solution, however, 50% full light treatment showed steady
decline in LWR whereas full light treatment showed rapid
increase followed by rapid decrease resulting in symmetrical
curve.
Lowering nitrogen level increased the value
of
LWR(Fig.
3.62).
Low-calcium treatment also showed higher
values of LWR than full nutrition treatment~
103
3.6.
Root length/leaf area and root number/leaf number
ratios
Root length/leaf area ratios are
shown
in
Figs.
3.63-3.65 for Expts. 2, 5 and 6, respectively. It is clear
in
Fig.
3.63
that
the
effect
of
low
solution
temperature(12.5 C) severely limited root length growth in
comparision to leaf area
growth
while
high
solution
temperature treatment(32.5 C) favoured the root length growth.
Fig. 3.64 shows that 5% full strength solution treatment
significantly enhanced root length growth compared to leaf
area growth under the full light and 50%
full
light
treatments.
However, lowering the light level to 10% full
light level lowered the root length/leaf area ratio in both
strengths of nutrient solution treatments. Lowering light
level to 50% full light also favoured the leaf area growth in
both strength treatments. Low nitrogen level in the solution
alone(Expt. 6) showed a significant increase in ratio of root
length/leaf
area
while
full nutrition and low-calcium
treatments showed almost same response with lower values.
I
I
The trends of root number/leaf
number
ratio(Figs.
3.66-3.68) are similar to those of root length/leaf area
ratio. The effect of low solution temperature was to reduce
the root number production compared to leaf number. Fig.
3.67 shows that the stress imposed on the root favours the
root number production while lowering the light intensity
enhanced the leaf number production.
As occurred in root
length/leaf area ratio, lowering light level to 10% full light
significantly reduced the ratio of root number/leaf number in
both strengths of solution.
Low nitrogen level in the
solution(Fig. 3.68) also increased the value of the ratio.
104
0.3
N
1
E
u
"E
0
.~
~
~
~
0.2
~
w
~
~
4~
W
"
~
~
en
c
w
~
0
0
~
~
o
1
2
3
4
time(week)
Fig.
3.63. The effect of diff~fent solution temperatures
on the root length eaf area ratio. *;12.5'C
+;32.5'C. Fitted va ues derived from Rlchards
function are plotted with 95% confidence limits.
105
0.6
N
-
/
E
u
E
.....o
0.4
/
+J
I1:S
So.
I1:S
(J)
So.
I1:S
I
4I1:S
(J)
..r::
+J
en
c:
(J)
...-
+J
0
0
So.
0.2
/
o
Fig.
1
I
/
I
/
/
/
/
/
/
/
/
I
I
/
I
/
I
/f/
/
;J/
/
I
I
2
I
/'
./
1--.
If
I
/'
I
I
I
/
/
/
/
/'
/,1
//1
I
L.
\
0
3
4
time(week)
3.64.
The effect Of different
solution
ionic
strengths
and llght intenslties on the root
lengtn/leaf area ratio.
full strength; o;full light 0;50% light ~;10% light
~%
strenyth; .;full light .;50% light .... ;10% light
Fitted values derlved from Richards functlon are
plotted with 95% confidence limits.
106
0.5
0.4
N
E
u
E
0
.j..J
It!
~
It!
Q)
~
It!
0.3
4It!
Q)
,......
.s::
+J
O'l
c:
Q)
,......
+J
0
0
0.2
~
0.1
o
Fig.
1
2
3
4
5
time(week)
3.65. The effect of different levels of nitrogen and
calcium on the root length/leaf area ratio. e;full
nutrition +;low-calcium *·low-nitrogen.
Fltted
vqlwes deri~~d from ~i~hards function are plotted
wlth Y5% contldence llmlts.
107
800
.
0
~
........
600
0
~
0
.,...
.f-l
n:l
~
~
OJ
.D
E
~
~
400
4n:l
OJ
........
~
OJ
.D
E
~
~
.f-l
0
0
~
200
o
Fig.
1
2
3
4
time(week)
3.66. The effect of different solution temperatures
on the root number/leaf number ratio. *;12.5'C
+;32.5'C. Fitted values derived from Rlchards
function are plotted with 95% confidence limits.
108
1500
1350
;"
/
I
I
I
---'~"1
/'
/
/
.
c
--....
.
I
I
0
'-.
I
0
c
I
0
.j.J
ro
~
900
/
~
OJ
..0
E
::l
/
c
4-
ro
OJ
--....
~
OJ
..0
E
::l
c
.j.J
0
0
~
450
l/
/
;"
o
1
/
I
/
/
/
/
A
I
/
/
/
/
/
•
/
2
3
4
tirne(week)
Fig.
The effect of different
solution
ionic
strengths
and light intensities on the root
number/leaf number ratio.
full strength; o;full light 0;50% light L!.;10% light
5% strength; .,full light _;50% light ... ·10% light
Fitted values derived from Richards funciion are
plotted with 95% confidence limits.
3.67.
109
1200
.
900
0
c
.......
.
0
c
0
+..l
It!
~
~
OJ
..D
E
::l
C
4It!
600
OJ
.......
~
OJ
..D
E
::l
C
+..l
0
0
~
300
T
o
1
2
3
4
5
time(~"eek)
Fig.
3.68. The effect of different levels of nitrogen and
calcium on the root number/leaf number ratlO •
• ·tul I nutrition
+. low-calcium *;low-nitrogen
Fitted values derivea from Richards functlon are
plotted with 95% confidence limits.
110
3.7.
Discussion
The data in the present study support
the generalized
concept of dry weight partitioning documented by a number of
authors(Dobben, 1962; Hegarty, 1973; Lambers and Posthumus,
1980;
Luckwill, 1960; Nelson, 1967; Nielsen and Humphries,
1966; Pandey and Sinha, 1977;
Szaniawski and Kielkiewicz,
1982;
Trought and Drew, 1981) that the allocation of dry
weight by plants between the root and shoot is influenced
differentially by the type of environmental stress to which
the plant is exposed. Davidson(1969a, 1969b), Hunt(1975) and
Hunt and Burnett(1973) are in agreement with these authors and
observed that in experiments in which they examined the
effects of different levels of shoot and root temperatures,
light intensities and nitrogen levels, the root/shoot mass
ratio followed a generalized concept that dry weight was
preferentially allocated to the plant organ whose function was
under stress.
From these observations they proposed that
externally induced decreases in the specific activities of
root or shoot systems would tend to be compensated by an
increase in the mass of the part of the plant whose function
was under stress in order for it to maintain the balance
between shoot and root activities.
The environmental stresses employed in the present study,
with
the
exception of low solution temperature(12.5 C)
treatment(Fig. 3.43), produced dry weight partitioning data
which tend to support this concept. The discrepancy with low
solution temperature may result from the fact that the
critical temperature for minimal effective root growth of
cucumber is thought to be about 15 C(Cooper, 1973), and the
low temperature treatment imposed in the present study was
maintained below this level. The effect was that the growth
of the whole plant was severely reduced even though the above
ground temperature was highly favourable for shoot growth.
Therefore the increase in the shoot/root mass obtained in the
low root temperature treatment(Fig.
3.43) resulted from a
relatively more severe reduction in growth of the root rather
than a stimulation of shoot growth.
I
I
.L .L .L
The equation 3.2 derived empirically by Davidson(1969a,
1969b) has been used by Hunt and Burnett(1973) and Hunt(1975)
to describe the relationship between the function of the root
and shoot. In addition to including a dry weight partitioning
term(root/shoot mass ratio), it also includes two terms to
describe the specific functional activities of the root and
shoot; the specific absorption rate(SAR) and unit shoot
rate(USR), respectively.
Hunt(1975) in his studies showed
that the USR decreased when plants were shaded but was
unaffected by nitrogen deficiency.
In the present studies
when plants were grown in full strength nutrient solution
shading had no effect on USR values(Fig. 3.36). Low levels
of nitrogen however increased USR values(Fig. 3.37).
The most significant discrepancy, however, between the
present data and those of Hunt and Burnett(1973) is that
shading to 10% of natural light increased the SAR with respect
to the sum of the three elements, potassium, calcium and
nitrogen(Fig.
3.40).
Their data showed that low light
intensity decreased the SAR values with respect to potassium.
In the present study even plants grown in the low nutritional
treatments and under 10% full light intensities showed higher
SAR values than plants grown in full strength solution and
full light treatments(Fig. 3.40). SAR represents the total
ion or ions absorbed per unit dry weight per unit time and
therefore it was surprising that plants supplied with only 5%
of the ions available compared with full strength solution
showed a higher SAR than those in the full strength solution.
In fact, the percentage potassium was higher in the shaded
plants although the roots grew poorly in terms of dry weight
gain.
Shading resulted in the plant allocating a
higher
proportion of its dry weight to shoot than the root which is
in agreement with Hunt(1975) and Hunt and Burnett (1971). The
argument made by Hunt(1975) and Hunt and Burnett(1973) infers
that the increase in shoot dry weight resulting from shading
can be compensated for by a decrease in SAR. However in the
present study both the shoot dry weight and the SAR increased.
Therefore it appears that for cucumber plants dry weight
allocation and specific activities of the shoot and root when
112
expressed
USR
and SAR do not respond to various
as
environmental stresses in the way Hunt(1975) and Hunt and
Burnett(1973) predicted.
Nevertheless, it is possible that the discrepancies in
SAR and USR between the present study and those of Hunt(1975)
and Hunt and Burnett ' s(1973) studies may be associated with
the fact that they used young perennial ryegrass seedlings
which lacked significant stem tissue.
They make the point
that the use of equation 3.2 lIis likely to be valid for young
grass plants or for dicotyledonous seedlings in which a very
high proportion of the shoot dry weight is leaf material". By
contrast the cucumber plants used in the present study had a
high
proportion of the shoot weight in the stem(Figs.
3.51-3.56). They also assumed that most of the root system
participated in absorbing nutrients and therefore dry weight
of the root could be considered as the functional size of that
organ.
For cucumb~r, at least in the present study, the
presence of stem can be a significant factor in its adaptation
to environmental stress.
Low root temperature treatment
enhanced the proportion of dry weight in the stem(Fig.
3.53)
and
lowered
the
LWR(Fig.
3.59).
Dilute
nutrient
solution(Fig. 3.54) and low-nitrogen(Fig.
3.56) treatments
reduced the proportion of stem weight but increased the
LWR(Figs. 3.60 and 3.62). Stem weight ratio(Fig. 3.55) and
LWR(Fig. 3.61) remained unchanged throughout the experimental
period when plants were grown in 10% of natural light.
Consistently lower values of SWR were obtained in Expts.
4(Fig. 3.54) and 6(Fig. 3.56), indicating that nutritional
stress stimulated root growth at the expense of stem growth
rather than leaf growth, thus preserving the photosynthetic
potential of the plant while allowing the plant to explore the
root environment. Most investigations of the role of the stem
in over-all plant growth have been concentrated on cereals
where the photosynthetic capacity of lamina and sheath is
considered important ~in the overall carbon balance of the
plant(Thorne, 1959) and with those deciduous trees and shrub
species in which considerable net photosynthetic capacity of
the stem is reported to occur(Perry, 1971). There is evidence
however that the stem may play a significant role in the
113
storage of organic and inorganic dry weight.
Richards and
Rowe(1977a) observed that physically restricting the roots of
pea c h (f.rU!! u~ ~e I"_~t ca L.) see d1 i ng s did not i nt e r fer e wit h the
role of the lower stem as a storage organ although this
treatment did reduce the dry weight of the other organs of the
plant. Loneragan et al (1968) in their paper on pasture plants
demonstrated the role of the stem in the storage
and
distribution of calcium. Causton and Venus (1981) suggested
that the high proportion of the dry weight allocated to the
stem by sunflower(Helianthus annuus L.) reflected the best
structural arrangement for such a high light demanding plant.
It seems reasonable to assume that the stems of plants
play an important role in the adaptive strategies and that the
inclusion of the stem dry weight in the shoot weight when
considering the functional relationship between the above and
below ground parts of the plant is justified.
However, Hunt
and Burnett(1973) recognized the conceptual difficulty of
including it when USR is used as the expression of specific
shoot
function.
Richards(1977,
1981) and Richards et
al(1979b) provided experimental evidence that under a wide
range of environmental stress a functional equilibrium between
the root and shoot does exist with a variety of species which
contain a high proportion of the dry weight in the stem.
However equation 3.2 is not a satisfactory expression of this
relationship as it assumes that all the dry weight allocated
to the shoot is involved directly in the photosynthetic
activity of the plant.
Similarly it assumes that all dry
weight allocated to the root is directly involved in the
nutrient and water absorbing activity of the root. A number
of authors have questioned this assumption and there is
considerable evidence to suggest that the absorptive activity
of the root system is not shared uniformly by all parts of the
root system.
Therefore the assumption which is made in
equation 3.2 that total dry weight of the root can be
considered as the functional size of the root-systems is also
open to criticism.
114
The poor empirical relationship between mass ratio and
l/activity ratio (equation 3.2) with Expt. 6(different levels
of nitrogen and calcium) and a reasonable
relationship
obtained with Expt.
5(different ionic strengths and light
intensities)(Fig. 3.19) implies that the use of weight of
roots as indicating functional size may not be appropriate for
certain environmental stresses.
Since root morphology is
influenced by different environmental stresses, it is logical
that the effective functional size of root may be different
according to the differential root morphology. Localized
application of nutrient induces the localized branching of
root(Drew, 1975, 1976; Drew and Saker, 1975, 1978; Hackett,
1968, 1972). In this case, the use of entire root weight
would not represent this compensatory response of morphology
and would not be an appropriate functional size.
Apart from the possibility that, like the stem, part of
the dry weight of the root may be available for storage, dry
weight can be organized in morphologically different ways
which may lead to a three dimensional structure which is more
or less efficient in terms of absorption activity.
Results shown in terms of root
number
and
root
length(Figs. 3.47-3.50) showed that the form of environmental
stress applied can
have
substantial
effects
on
the
morphological
structure
of the root.
Shallow solution
depth(Fig. 3.47) and low solution temperature(Fig.
3.48)
enhanced the number of roots relative to the total length of
the root system. High levels of nutrients in the root zone
increased the root number/root length ratio(Fig. 3.50) in
agreement with the data of Drew(1975) who worked with cereals.
Low nitrogen solution treatment stimulated root elongation
relative to root number, thus producing a decreased root
number/root length ratio(Fig.
3.50). This is in agreement
with the work of Bosemark(1954) which showed an inverse
relationship between root development and_ nitrogen supply and
he concluded that the increase in root length under nitrogen
deficiency was primarily due to an increase in cell length and
reduced cell multiplication.
11~
The conclusion that dry weight alone does not adequately
represent the functional root size can also be implied from
the work of other authors. Veen(1977) concluded that neither
root volume or root weight were as good parameters with
respect to nitrate uptake by maize as root surface area.
Expressions
such
as root surface area/weight of p1 ant
correlated well with potassium concentration in the shoot
(Woodhouse et al, 1978). Similar expressions, such as root
absorbing surface area/shoot weight were also
used
by
Powell(1974) who found that when phosphorus levels increased
roots became thicker and surface area/shoot weight ratio
decreased. The phosphorus response was better correlated with
this ratio than with the root/shoot mass ratio.
Veen(1982)
showed that mechanically impeded crown roots of maize resulted
in up to a 50% increase in root diameter and a decrease in
root length.
As discussed earlier, using root dry weight to represent
the functional size of the root ignores all the subtle
responses which may affect root activity.
Ferguson and
Clarkson(1976) showed that calcium uptake and translocation to'
the shoot occurred in the unsuberized zone near to the root
apex.
Absorption and translocation of nitrogen and potassium
were less affected by the age of the root axes(Troughton,
1981).
This implies that surface area of unsuberized root
would be a better functional size parameter for cal~ium,
whereas
total surface area of the root axes might be
acceptable for nitrogen and potassium. As a result of these
observations Troughton(1981) warned that nutrient absorption
data obtained with young plants might be different from those
obtained with older plants.
Work by Graham et al(1974) in
which water uptake by seminal axes and primary laterals was
compared shows that water absorption is closely related to the
morphology of the root.
However, in some cases, mineral
absorption does not appear to be related to root morphology.
McLachlan and De Marco(1982) showed that total phosphorus
uptake was not affected by such things as root weight, length
or fineness. In light of these reports it is understandable
that Hunt and Burnett(1973) were cautious about using equation
3.2 which assumes that the entire root system is active in
116
absorption aciivity. The presence of a small number of roots
on the stems induced by some treatments in the present
study(see Appendix 3) had a significant effect on the growth
of such plants. The fact that these "aerial roots
existed
above the nutrient solution negated their involvement in the
absorption of mineral elements.
However as shown in the
Appendix 4, a linear relationship exists using equation 3.2
only when the weight of those roots i~[ used in the SAR term.
Such an anomaly can only be explained if it is assumed that
root system has other functions in addition to absorbing
nutrients and water.
ll
While Richards(1977, 1978) in his experiments with both
equations 3.2 or 3.3 showed that an equilibrium relationship
was established, a comparison of equations 3.2 and 3.3 in the
present
study
describing
the
functional
equilibrium
relationship between shoot and root over a wide range of
environmental conditions showed that equation 3.3 generally
produced a better relationship than equation 3.2 throughout
all the experiments.
In the data from Expts. 2 and 3 as
shown in Figs. 3.1-3.4 and 3.13, there were significantly
graded lines produced, depending on the solution temperature.
However, the relative value of slopes in each experiment was
also different, i.e. in the Expt. 2 low solution temperature
treatment showed a lower slope whereas in the Expt.
3 a
higher slope.
The higher slope of the line represents a
relatively large increase in the
root/shoot
ratio
in
comparision to the small increase in l/activity ratio. In the
case of Expt. 2, highly restricted root growth due to the
sub-optimal
solution
temperature
resulted in the high
shoot/root ratio as shown in Fig. 3.43 and interestingly the
percentage of potassium in the leaves showed the same values
regardless of temperature treatments(Table 3.1). However, in
the
case of Expt.
3, a relatively large increase in
l/activity ratio was accompanied by a small increase in
root/shoot ratio when high temperature was applied, producing
a lower slope. This may be due to the fact that the duration
of Expt. 3 was much longer and solution depth treatments were
imposed. The longer duration of the experiment with shallow
depth of solution(5mm) eventually created plants with a large
117
proportion of their root system exposed to the air.
The
exposure of part of the root system in the shallow treatment
coincided with a drop in the percentage of potassium in the
leaves as shown in Table 3.2. The implication is that the
exposure of part of the root system to the air leads to a
reduced uptake of potassium by the plant. Combined with an
increase in the proportion of dry weight allocated to the root
relative to the shoot this leads to a decrease in the SAR in
the equation 3.2 and thus producing the lower slope of the
1 i n e.
Equation 3.2 provided tolerable
relationships
when
different levels of ionic strength of solution(Fig. 3.16) and
light intensity(Fig. 3.19) were applied. While equation 3.3
produced a good relationship when different temperatures were
applied, there existed significantly different gradients,
depending on the root environment, for example low versus high
ionic strength(Figs. 3.17 and 3.20) and the different levels
of calcium(Fig.
3.26) and nitrogen(Figs. 3.29 and 3.32).
The problem associated with clustering of points near to the
origin due to poor plant growth was inevitable when equation
3.3 was used. But as can be seen in Fig. 3.26, this problem
can be completely overcome and there existed significantly
different gradients with well scattered points along the
fitted line, one being low-calcium and the other being high
calcium treatment. It is concluded that both equations failed
to establish the functional equilibrium relationship with
calcium(Figs. 3.25 and 3.26) when different levels of calcium
were applied. Hence, as was pointed out by Chung et al (1982),
equation 3.3 may be of biological significance in that
cucumber plants adapt to nutritional stress by decreasing
uptake of elements relative to its total dry weight(Figs.
3.17, 3.20, 3.26, 3.29 and 3.32).
The possibility of a two line relationship with respect
to equation 3.2 was acknowledged by Hunt(1976) even though the
data fitted well with a single linear line.
Richards(1978)
also showed that there existed clearly graded lines, w)th
respect to equation 3.3, depending on
the
levels
of
6-benzylaminopurine applied to the peach plants. The dilemma,
however, as shown in the present studies is that significantly
118
graded lines exist and data could not be fitted with
while a functional equilibrium relationship infers
line relationship. Moreover, the relative value of
also varied when different sets of data with
treatments were examined(Expts. 2 and 3).
one line,
a single
the slope
the same
Thorn1ey(1977) claimed that equations 3.2 and 3.3 may be
mathematically the same, because the multiplication of the
same factors into both sides of equation 3.3 eventually
produces equation 3.2. However, the basic reasoning for each
equation was different, in that Hunt(1975) derived
his
equation empirically from the suggestions put forward by
Davidson(1969a, 1969b) while Thornley(1972)
derived
his
equation theoretically. The argument between Hunt(1976, 1977)
and Thornley(1975, 1977) appears to
be
that
Thornley
emphasizes the mathematical relationship and Hunt prefers to
find the biological signific~nce. From the biologist's point
of view, it is more interesting to determine the mechanism of
adaptation in which activities of shoot and root can be
investigated
rather than the precise estimation of the
relationship itself. In addition to the non-existence of an
equilibrium relationship, the kind of precision in equation
3.3 seems guaranteed to produce a better relationship because
total weight of elements is calculated by multiplication of
the total weight of plants by the percentage of elements in
the plants.
Hence, the prime controlling factor in equation
3.3 is the total plant dry weight regardless of the importance
of partitioning of dry matter between shoot and root and of
the different specific activities of each organ.
While
conflicts between Hunt(1979, 1981) and Thornley(1980) have
been extended on the matter of empirical versus mechanistic
models, the present experimental results showed that neither
equation satisfactorily established a functional equilibrium
relationship between shoot and root.
The equation proposed empirically by Chung et al(1982)
markedly improved the functional relationship compared to
equat i on 3.2 while it showed virtually the same result as
equation
3.3
when different solution temperatures were
applied(Figs.
3.9-3.12).
When
equation
3.3
produced
significantly
graded
lines
according
to
the
root
119
environment(Figs. 3.17, 3.20, 3.26, 3.29 and 3.32), equation
3.5 showed a good single line relationship(Figs. 3.18, 3.21,
3.30 and 3.33) with the exception of calcium in the Expt.
6(Fig.
3.27).
Therefore it is apparent that equation 3.5
represents a better functional
equilibrium
relationship
between shoot and root than the other two equations, at least
with cucumber.
The experimental results with respect to
equation 3.3, published by Chung et al (1982, see Fig. 1a in
Appendix 6) contained a problem in that the data produced with
low solution strength treatment did not show a large enough
range and had clustered points even though slope of the line
was
significantly different from full strength solution
treatment{Fig. 3.17). At the same time, results plotted in
the form of equation 3.5 also produced a clustering of points
near to the origin, due to poor plant growth(Fig.
3.18).
However,
these
difficulties
arlslng from a poor data
range{with equation 3.3) and clustering
of
points(with
equations 3.3 and 3.5) were partly solved in Expts. 5 and 6.
The results obtained from Expt. 5 not only confirmed those of
Expt. 4 that different slopes of the lines were based on root
environment with respect to equation 3.3, but also solved the
problems associated with the linear regression in that the
line produced with low ionic strength treatment covered a
greater range of data points(Fig. 3.20). The result obtained
with equation 3.5 also showed an improvement in terms of
actual data pOints along the fitted line(Fig. 3.21). Results
of Expt. 6 with respect to calcium uptake(Fig.
3.26) with
equation 3.3 also confirmed the previous findings in that the
fitted line was longer and the different slopes of the
regression lines were related to the nutrient level of the
treatment.
The effect of environmental stresses employed in the
present studies such as ionic strength, nitrogen level and
light intensity on the ratio of root length/leaf area(Figs.
3.63-3.65)
and root number/leaf number(Figs.
3.66-3.68)
showed similar trends as the shoot/root ratio shown in Figs.
3.42-3.46.
Low solution temperature severely restricted both
root length and root number growth(Figs.
3.63 and 3.66).
However, the degree of reduction in absolute leaf number in
120
low solution temperature treatments was 4 times less than leaf
area growth at the final harvest compared to high temperature
treatments.
Lowering ionic
strength
of
the
solution
significantly
increased
the ratios of root length/leaf
area(Fig. 3.64) and root number/leaf number(Fig. 3.67), but
the degree of reduction was always greater in leaf area than
in leaf number suggesting that the root length growth was
achieved at the expense of leaf area growth.
This was
confirmed again in Expt. 6 in which lowering the nitrogen
level also favoured the growth of root length(Fig. 3.65) and
root number(Fig. 3.68), but the reduction in leaf area in
low-nitrogen treatment was about twice that of leaf number.
From these observations, it seems clear that the form of
stress
can
be
expressed
in
terms
of morphological
relationships between shoot and root. It is acknowledged that
such morphological relationships are essentially based on
empirical hypothesis. However, these relationships can be
biologically significant because surface area is the basic
parameter for absorption of mineral elements and CO
and it
2
was considered in the present studies that the length of roots
would provide a good approximation of the surface area of the
root system. The involvement of root hormones produced in the
root tip(number of roots in the present studies) may also be
implicated in shoot differentiation and production of new
leaves(Atkin et al, 1973; Barlass and Skene, 1980;
Skene,
1975).
Comparative reduction in leaf area and in leaf number
when low solution temperature was applied as discussed earlier
suggests that the resources available in the shoot are
primarily used in the production of leaf number rather than in
leaf area.
The final outcome of the shoot morphology was
therefore to maintain leaf number production with small
individual leaf area.
Changes in root and leaf morphology
therefore appear to be intimately associated with the plants
adaptive strategies when under stress.
That the root morphology is an important factor in
absorptive function is well recognized. However, the effect
of differential shoot morphology on the shoot functioning has
been less understood, the conventional measurement being shoot
dry weight. A typical example of this is the plant growth
analysis technique(Evans, 1972;
Hunt, 1978) which assumes
equal photosynthetic capacity of all leaves.
However, there
is evidence that different shoot morphology affects CO
2
fixation.
Austin et al(1976) showed with wheat(Triticum
aest_ivum L.) that the photosynthesis was greater when the
upper leaves are erect.
Hopkinson(1964) presented evidence
that the leaves of cucumber differ in the pattern of import
and export of carbohydrates.
As Bazzaz and Harper(1977)
suggested,
it
is necessary to IIbreak down
the crude
phenomenon of growth into various components to study the
influence of environmental stresses.
Demographic analysis
concerned with the number of plant modules was developed with
forest trees(Lovett Doust, 1981) and shrubs(Kempf and Pickett,
1981).
Porter(1983a, 1983b) emphasizes the necessity of
considering the whole plant morphology and development in
terms of changes in the numbers, not only the size.
While
Bazzaz and Harper(1977), and Porter(1983a, 1983b) acknowledged
the effect of shoot morphology on the efficiency of shoot
functioning,
the
consequences
of
the
changed aerial
environments on root morphology were not studied.
It is
suggested that the direct effect of environmental stresses may
be better understood in terms of morphological responses in
shoot and in root which may affect the efficiency of the
organ. This concept is supported by Brom'ler(1977) who pOinted
out that the use of dry weights of shoot and root in
functional equilibrium equations lacks biological significance
due to the fact that dry weight alone does not account for
subtle morphological relationships and their influence on the
function of other organs.
ll
The basic concepts of using ratios of root number/root
length and leaf number/leaf area used in equation 3.5 are two
fold. First, these ratios are useful descriptions of the
morphological response of both organs as they are an index of
the three dimensional nature of shoot and root structure.
Second, intimate morphological relationship between shoot and
root, rather than dry weight alone, exists as shown in Figs.
3.63-3.68.
It
is noted that the relationship between
morphology of shoot and root showed similar trends to weight
terms(Figs.
3.42-3.46). However, it can be argued that root
122
length and root number are broadly correlated with root dry
weight because their existence depends on structural dry
weight. But because of the complexity of the morphological
adaptation of the root system to different environmental
stresses the relationship between dry weight and each of these
parameters will change according to the stress applied.
Experimental results shown in Figs.
3.63-3.68 confirm this
view, i.e.
the effect of low solution temperature in which
lack of root extension growth(Fig. 3.48) was matched by the
shoot having small leaf area with relatively high leaf number,
while the lowering of light intensity increased the leaf area
growth
at
the
expense
of
root length.
From these
observations, morphological descriptions were included in the
equation 3.3, which became equation 3.5 to test the hypothesis
that the functions of root and shoot are derived from their
differential morphology.
This hypothesis was supported by
experimental results with equation 3.5 in this Chapter which
showed a better relationship than equations 3.2 and 3.3(Figs.
3.18, 3.21, 3.30 and 3.33).
Equation 3.5 implies that absorption and translocation of
particular elements seems not the sale activity of particular
components of equation 3.5. Measurement of root parameters
such as root fresh weight, root dry weight, root length and
root surface area by Sachan and Sharma(1981) with
the
calculation of amount of calcium in the leaves may be
misleading because of the effect of the shoot in absorption
activity of root.
If the absorption and translocation of
calcium is solely dependent on the root morphology, then the
claim made by Sachan and Sharma(1981) for estimating root
length by simply measuring calcium content may be correct. In
fact, regression analysis on the relationship between root
length and calcium content in the shoot showed two clearly
graded
lines(see
Appendix
5).
The argument is that
photosynthate manufactured in the leaves can be primarily used
in the root if the demands from roots are high and at the same
time any particular element
can be easily absorbed and
translocated to the shoot if the demands from shoot are in
excess of roots. The concept of demand on the functional
equilibrium relationship will be discussed in Chapter 4. It
~
123
is acknowledged that equation 3.5 is a
highly
empirical
equation at this stage, but it represents the involvement of
morphological structures in the total activities of shoot and
root.
In conclusion, equation 3.5 was a superior expression of
the functional equilibrium relationship between shoot and root
with the exception of data on calcium.
The probable reason
for the poor relationship obtained from equation 3.2 may be
the fact that the specific activities of root(SAR) and
shoot(USR) did not follow the prediction that Davidson(1969a,
1969b), Hunt(1975) and Hunt and Burnett(1973) made.
They
assumed that the entire shoot and root participate in their
specific functions. However, it is argued that the best
estimate of the the functional size of root may not be the
root dry weight. Equation 3.3 may be used to describe the
biol'ogical significance produced from two line relationships.
The inclusion of morphological characteristics such as used in
equation 3.5 expresses a wide range of possible adaptation
processes by both shoot and root.
124
CHAPTER 4
THE IMPLICATION OF SOURCE-SINK RELATIONSHIPS
ON THE FUNCTIONAL EQUILIBRIUM
RELATIONSHIP BETWEEN SHOOT AND ROOT
4.1.
Introduction
In the empirical equation proposed by Davidson(1969a,
1969b, equation 3.1) and subsequently used by Hunt(1975,
equation 3.2) and Hunt and Burnett(1973), the
specific
absorption
rate and the unit shoot rate represent the
activities of the source of mineral uptake and photosynthetic
products, respectively. The form of the equation embodies the
basic concept that the ~ctivity of each source is dependent on
its mass.
The equation 3.5 developed by Chung et al (1982)
involves essentially the same concept but introduces an
additional idea first proposed by Richards and Rowe(1977a,
1977b) that the functional size of the root or shoot is better
approximated if the equation includes the morphological terms
of root number and length and leaf number and area. As shown
in the previous Chapter, equation 3.5 described the adaptive
growth of cucumber under a wide range of environmental
stresses,
better
than
the
Davidson(1969a, 1969b) and
Hunt(1975) equation and provided a much better description of
some of the biological processes involved in adaptation of
cucumber plants than the simpler equation
proposed
by
ThornleY(1972).
Warren-Wilson(1972), Wareing
and
Patrick(1975)
and
Herold(1980) proposed that for balanced plant growth the
activity of the source had to be equal to the demand of the
sink.
The equations proposed by Davidson(1969a, 1969b),
Hunt(1975) and Thornley(1972) appear to encompass this concept
as they assume~that the maintenance of the balanced function
of the shoot and root is achieved by the plant directing dry
weight to and/or adjusting the morphology of the organ whose
function is under stress.
125
The problem, however, is that these equations do not
incorporate the notion that the specific activity of the root
or shoot as a source is influenced by the demand in the
opposite organ acting as a sink for the products of the
function of the opposite organ. The difficulty arises from
the fact that the root and shoot, as a result of their
metabolic activities, growth and storage potential, can be
both source and sink at the same time. The idea that sink
demand has a strong influence on the activity of the source
finds considerable support in the literature.
Hatrick
and
Bowling(1973),
after
measuring
the
respiration
rate
of
roots and nutrient translocation,
concluded that nutrient uptake by barley and sunflower roots
is regulated by the activity of the photosynthetic parts of
the plant. Pitman(1972) showed that potassium transport was
directly proportional to the relative growth rate of the shoot
in barley. Nye and Tinker(1969) introduced the concept of
plant demand in which the "driving force" for absorption at
the root surface is provided by the growth of the plant.
Cumbus and Nye(1982) demonstrated that the effect of low
s~lution temperature was not mediated through the shortage
of
nitrogen but the consequent low demand of the shoot which
exerted a controlling influence on the nitrate uptake through
the
available
root.
Further
evidence
was shown by
Jeschke(1982) that the root of barley can increase its rate of
ion uptake and xylem transport in response to demands of the
shoot. Humphries and Thorne(1964) showed that photosynthesis
and respiration of dwarf bean(Phaseolus vulgaris L.) decreased
when root growth was inhibited and indicated that the size of
the root, which is a sink for photosynthesis, is correlated
with the activity of the shoot. This demand concept was also
shown by Richards and Rowe(1977a, 1977b), who demonstrated
that the controlling mechanism of water uptake by the peach
plants is not by dry weight accumulation but rather involves
the transpirational conditions and the leaf area.
The
implication is that water absorption is a function of leaf
area rather than that of size of the root system.
By
comparing different varieties of sweet potato, Hahn(1977)
clearly showed that carbon assimilation and translocation rate
126
influenced by sink activity.
Thorne and
were markedly
Koller(1974) also concluded that source-leaf photosynthesis
rate and carbohydrate export were markedly influenced by
assimilate demand in other parts of the plant.
The work of
others(Barber, 1979; Wild and Breeze, 1981; Drew and Saker,
1978) indicate that nutrient absorption is influenced by the
demand of the plant created by additional growth and a
feedback mechanism exists which coordinate the functional
activities of the shoot and root.
Herold(1980) proposed that this feedback mechanism may be
mediated
by
three
factors;
hormones,
carbohydrate
accumulation and orthophosphate concentration, which act as
messengers in coordinating the shoot and root interactions.
Hormones, in particular, have attracted much attention.
It
has been suggested by numerous authors that shoot development
is dep~~dent on hormonal production in the root.
Direct
evidence that the root supplies the vital signal for protein
metabolism was shown by Chibnall(1954) when he~ demonstrated
that
senescence of runner bean leaves was arrested if
adventitious roots
grew
on
the
petioles.
Exogenous
application of cytokinin to Xanthium leaves prevented the
degeneration of protein and chlorophyll and thus replaced the
effect of the presence of roots(Richmond and Lang, 1957).
Moreover, cytokinin levels in the shoot appear to exert
control over the shoot growth. Horgan and Wareing(1980) found
that there ~as a rapid stimulation of growth of inhibited
shoot apices and lateral buds after external application of
cytokinins to nitrogen-deficient birch seedlings, indicating
that
apical
dominance
was mediated through endogenous
cytokinin produced in the root. Jeschke(1982) also indicated
that the incr~ased xylem transport of K and Na in barley
plants 'in which a high shoot/root ratio was induced was
created by an increased demand in the shoot mediated through
cytokinin.
)
The clearest experimental evidence that the demand by the
shoot affects the absorption activity of root was shown by
Clarkson(1981) with tomato and Lee(1982) with barley, who
concluded that the rate of phosphorus uptake by plants was
influenced by the nutritional history of the plant;
the
1L /
uptake
rate
being higher where plants were previously
phosphorus stressed.
~his
is
in
agreement
with
the
observation of Graham and Bowling(1977), who, after observing
the effect of light, darkness,
ringing,
excision
and
externally
supplied
sucrose,
suggested
that
membrane
potentials of root cells closely related to processes going on
in the whole plant, not just in the root. This kind of
integrated response
of
plants
influenced
by
various
environmental conditions can be seen in Fig. 4.1 drawn by
LUttge and Higin~otham(1979) after Cram and Pitman(1972) and
Pitman(1972).
It infers that information from the shoot can
be
transmitted
to
the
root
stimulating
ion-uptake.
Experimental evidence obtained from Expt. 5 in the present
studies support this view.
The specific root
activity
expressed in terms of SAR(Fig. 3.40) showed that the plants
grown under a given strength of nutrient solution with 10%
full light intensity had the highest percentage of potassium
and calcium and hence the highest SAR value.
Light stress
enhanced the root absorption activity, exceeding that of
plants grown under solution strength 20 times higher and under
full light intensity. The inference is that plants are able
to regulate the absorption of ions from the diluted solution
to match the demand of the shoot. Clarkson(1982) argued that
maximum affinity of the ions is not fixed and showed that
affinity can far exceed these maximum values in response to
the demand of shoot.
He concluded that the physiological
condition of the plant affects the absorption activity of root
contradicting the long-held hypothesis that nutrient uptake
was controlled solely by the ion concentration outside the
root.
128
LEAF
ION CONCENTRATION
SUBSTRATE CONCENTRATION
HORMONE LEVELS
-------------------------------------------------------------
------)
T
1
~
PHLOEM
TRANSPORT
LEAF FREE
SPACE
I
1
FEED-BACK
EXPORT
I
HORMONE LEVELS
ION CONCENTRATION
t
SUGAR CONCENTRATION
~
--------------------------UPTAKE------------------------------ROOT
Fig.
4.1.
Model for commmunication and coupling between
shoot and root drawn by LUttge and
Higinbo~ham(1979) after Cram and Pitman(1972)
and Pitman(1972).
129
As shown by the data in ~ig. 3.37 low nitrogen levels in the
solution enhanced the specific shoot activity expressed as
USR. Nutritional stress imposed on the root was mediated
through the increase in the specific activity of the shoot.
This is contradictory to the view of Davidson(1969a~ 1969b)
and Hunt(1975) who proposed a functional equilibrium based on
the equations 3.1 and 3.2.
The present experimental results and the observations of
other workers such as Pitman(1972), Jeschke(1982), Lee(1982)
and Clarkson(1982), therefore, indicate that specific activity
of one organ is influenced by stress applied to the opposite
organ. Consequently, total root activity may be described by
the following equation,
shoot mass x specific root activity=total root activity--4.1
By the same principle, total shoot activity may
as,
be
expressed
root mass x specific shoot activity=total shoot activity--4.2
Based on the assumptions made
Hunt(1975) and Thornley(1972),
equated, and become;
by Davidson(1969a, 1969b),
equations 4.1 and 4.2 may be
shoot mass x specific root activity a root mass x specific
shoot activity-------------------4.3
Expressing the equation in the terms proposed
1976), the following equation may be derived.
by
Hunt(1975,
shoot/root ratio ai/activity ratio(SAR/USR)------------4.4
While the form of equation 4.4 is simply the reciprocal of
mass ratio in the equation 3.2, the basis of deriving it is
entirely different from that put forward by Davidson(1969a,
1969b).
It implies that absorption and translocation of
minerals are not solely under the control of the root, and
carbohydrate production may not be solely under control of the
leaves. In agreement with Drew and Saker(1978), Gersani et
al (1980), Jeschke(1982) and Pitman(1972), it recognizes that a
130
feedback mechanism exists between the shoot and
influences the function of the opposite organ.
Equation 4.3 may be rewritten in the
equation,
form
root
which
of
following
(plant mass/shoot mass/day) x root mass a ("k "/root
x shoot mass--------------4.5
mass/day)
where "kll represents ion(s) or compound(s) taken up by plants.
After cancelling the l/day from both sides of equation, the
following equation may be derived,
(plant mass) x (root mass) x (root mass)
x (shoot mass)---------------4.6
a
"kl!
X
(shoot
mass)
It is difficult to deduce, at least at this stage, any
specific biological significance with particular respect to
the square of root and shoot mass in equation 4.6. However it
is the mathematical result of using shoot and root mass as
their functional sizes, as suggested by Davidson(1969a, 1969b)
and Hunt(1975) when multiplied by size of opposite organ
provided two conditions are accepted. Firstly, SAR and USR
realistically represent the specific activities of root and
shoot. Secondly, equation 4.6 is another way of expressing
equation 4.4.
Equations 4.4 and 4.6 may be viewed as
different equations as considered in the Chapter 3 with
respect to equations 3.2 and 3.3, and the only important
difference between equations 4.4 and 4.6 compared to 3.2 and
3.3 being the multiplication of the mass of the opposite organ
with the specific activities of organ being considered.
In this Chapter, experimental data will be presented
using equations 4.4 and 4.6 to see whether they represent
functional equilibrium relationships between shoot and rOQt
better than the equations discussed in the Chapter 3.
Where a curvi-linear relationship results
the data, the following equation is used,
from
plotting
b
Y=aX ---------------4.7
where Y is the shoot/root ratio, X is the
l/activity
ratio(SAR/USR) and a and b are the constants. This curve is
1 J L
fitted to the data by fitting
log-transformed data,
a
straight
line
through
the
log(Y)=log(a) + b.log(X) ------------4.8
Since the argument was made in the previous Chapter that SAR
and
USR were not good representations of the specific
activities of root and shoot in the case of Expt. 2(different
solution
temperatures) and Expt.
6(different levels of
nitrogen and calcium), only Expi. 4(different levels of ionic
strengths, depths and volumes) and Expt. 5(different levels
of ionic strengths and light intensities) in which equation
3.2 showed a tolerable relationship were used to test the
validity of equation 4.4 with respect to the total sum of
measured ions.
In the case of equation 4.6, total sum of
measured ions will be used with the experimental data obtained
from Expts. 2, 4, 5~ and 6. In addition, these two equations
were applied to the data with respect to calcium uptake from
Expt.
6 to see if a functional relationship exists since, as
shown in Chapter 3, equations 3.2, 3.3 and 3.5 failed to
satisfactorily describe a relationship.
132
4.2.
Results
Data from Expt. 4(different ionic strengths, solution
depths and volumes) plotted on the basis of equation 4.4 with
respect to the sum of K and Ca uptake are shown in Fig.
4.2.
It
is
clear that curve produced is not linear.
The
correlation coefficient calculated from fitting equation 4.8
was -O.811.
Results plotted with individual elements also
showed curvi-linear relationships.
Results obtained from Expt. 5(different ionic strengths
and light intensities) using equation 4.4 are shown in Fig.
4.3. As in Fig. 4.2, the relationship plotted with respect
to the sum of K, Ca and N uptake was clearly curvi-linear with
a correlation coefficient(r=-O.986) calculated from fitting
data to equation 4.8.
r----~T-
24
1
~----r------.__------r
r
r-
,
+
22
~
20
18
t::)
"t::)
16
214
t-
'"
o:
a:: 12
to
a
a:::
"-
l
+ '"
'" +4
10
t-
o
:r:
0
(f)
..
8
• ,J, '.
",
6
+
...
, '+.
4
*
oj<
+ '"*
+
+
'"
+"'+
.f.
*
*+
-tft. **+ * '" + +
**
**+ +
+
+
oj<
2
0
0
2
4
+ +
~
oj<
6
t
oj<
*
*"*
*
+
+
+t<
8
l/ACTIVITY RATIO WITH RESPECT TO SUM OF K AND CR
Fig.
4.2.
*
oj<
+
10
12
*
1
-j
14
(G/G/DRYl I (G/G/DAY)
The effect of different SQlution ionic stren~ths, deptbs and
volumes on the relatlonshlp between the shoot/root ratlo and
the reciprocal of actlvity ratlo with respect to sum of
~otassium
and ~alcium uptake •• ;full strength +;5% strength
;2% strength.
Depth and volume treatments were excluaed
from the symbols
>-'
W
W
40
+
35
30
+
+
C)
"'C)
25
0
I-i
1-
I-
~ 20
fD
+
*
~
0
a:::
*'-*,ft
"'I- 15
0
D
~iJ
:r:
If)
~W-
10
~-ttit-
t t
+
+ ++
5
o
o
LI_ _L-~
* * * **
:f\j<
** * * **** ,..** ** *~
,* *
*
__~~L-~__~__~-L__~~__-L__L-~__~__L-~__~__~-L__~~__-L__L - - J__~__L-~__~__~-J
.2
Fig.
t
.8
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
.6
1.0
1.2
.4
l/RCTIVITY RRTIO WITH RESPECT TO SUM OF K, CR RND N (G/G/DRYJ/(G/G/ORYJ
4.3.
The effect of different solution ionic strengths and liqht
intensities on the relationship betw~en the shoot/root ratio
and the reciprocal of actlvity ratio wlth respect to sum of
potassium, calcium and nitrogen uptake. +;full strength *-5%
strebngth). (Light intensity treatments were excluded from the
sym oTs
3.0
.......
w
+::>
135
Data from Expt.
solution
temperatu re)
2(different
plotted using equation 4.6 with respect to the sum of K, Ca
and N uptake showed a linear relationshi~(r=O.995)(Fig. 4.4).
Figures 4.5 and 4.6 which represent data plotted from Expt.
4(different ionic strengths, solution depths and volumes) with
respect to the sum of K and Ca uptake and Expt. 5(different
levels of ionic strengths and light intensities) with respect
to the sum of K, Ca and N uptake produced two lines which were
significantly(p<O.05) different and were dependent on the
ionic strengths in both experiments.
The .line with the
steeper slope represents the low strength
of
solution
treatment.
Plotting the data from Expt. 6(different levels
of nitrogen and calcium) with respect to the sum of K, Ca and
N uptake showed a significantly(p<O.05) different three line
relationship(Fig.
4.7);
the
highest
gradient
being
low-nitrogen treatment and the lowest low-calcium treatment.
Points near to the origin on Figs. 4.5, 4.6 and 4.7 are shown
overlays.
Equations 4.4 and 4.6 were used to plot the data of
calcium uptake in Expt.
6(different levels of calcium and
nitrogen) which showed no equilibrium relationship with the
equations used in the Chapter 3. Equation 4.4 did not show a
good relationship (Fig. 4.8). It can be seen in Fig.
4.9
that
there
are
three
lines
which are significantly
different(p<O.05) depending on the levels of calcium and
nitrogen applied.
o
o
o
CO
*
,
**
+
+
•
+
*
t*
o
oIn
10 3 x21
22
f
"I~
.--.--- r
I
I
I
I
I
I
I
,
J
1
t
I
I
I
I
I
~
I
I
I
I
I
x
I
I
I
I
,
,
I
'/'-'1
'
~
l!)
l!)
I
/'
/~
I
20
N
I
18
~
16
N
I--
3:
I--
o
o
a::::
><
.
~
1
14
1
12
1
10
a::::
0
I-Z
a:
---1
£L
l
+
>-
l
8
+//
6
+
L
'1
~
2k:
0
0
+
!
5
10
15
20
25
30
35
TOTRL SUM OF K,CR RND N CONTENT x SHOOT WT2.
Fig.
4.4.
The effect of different solutiQn
relatiQnship between (plant weight) x
weight) and the {total sum of potassium!
nitrogen) x (shoot weight) x (shoot
+;32.5 C.
Y=O.0576X+92.2;
r=O.995.
origin are shown on the acetate overlay)
I
!
~
!...L-.l
45
(GxG 2 )
temperatures on the
(root weight) x (root
calclum and
weight).
*;12.5'C
(Points near to the
........
W
0"\
..
+
+
*
+
..
*
+
*
*
++
+ +
10 4 x
180
160
/
N
~ 110
C)
Nt-
:r:
C)
1
~
120
t-<
1
W
3:
100
t-
o
0
cr::
~
:r:
80
C)
W
3:
>cr::
60
0
t-
z
IT
10
-1
D-
20
0
10
0
20
30
10
50
60 X105
TOTRL SUM OF K -RND CR CONTENTxSHOOT WT~
The effect of different solution ionic strengths and- depths
on the relationship between {plant weight) x (root weight) x
root weight) and the (totQl s~m of potassium and cglcium) X
shoot wefght) x (shoot welght • • ;full strength +;~'A> strength
-2% strength. SloDe and con idence limit for 5 plus 2%
strength, and full strength are; 1.958±O.131, O.283±O.0213.
(Points near to the origin are shown on the acetate overlay.
Depth and volume treatments were excluded from the symbols)
70
( GXG 2 )
Fig.
4.5.
I
i-'
W
'-l
+
+
*
++
+
..
+
*
+
.
+
+
"
+
+
10 2x 2':1:0
220
200
N
C)
180
x
C)
160
N°
~ 1':1:0
t-
o
oe:::
120
x
°
5: 100
>e:::
0
+
80
IZ
a:
.-1
CL
60
+
~
+
':1:0
20
~,rl
"
Fig.
I
I
I
I
30
35
40 X10 4
TOTRL SUM OF K, CR RND N CONTENT x SHOOT WT~
(GxG 2 )
4.6 •. The ~ffect of different solution ionic strengths and light
lntensltie$ on the re1ltlonship between (plant weight) x (root
weight) x troot weight
and the (total sum of potassium,
calcjum and nitrogen
x (shoot weight) x (shoot weight).
+jfUI I strength ;o~ s rengtn. Slope and confidence limit for
5~
strength
and full strength treatments are;O.505±O.0288,
O.0578±O.006j. (Light intensity treatments were excluded from
the symbols.
Points near to the origin are shown on the
acetate overl ay)
5
10
15
20
25
45
I-'
W
OJ
10 2 Xl10
100
~
+
/
+
+
90
N
C)
><
C)
N'
f-
3:
80
70
~
/
/+
f-
a
a
0:::
60
x
f-
I
C)
50 I-
w
3:
>0:::
0
f-
4:0
+
/
........
/
L
+
/
30 I
+
./
+
Z
a:
.-J
CL
20
10
1
2
6
8
10
12
11
16
TOTRL SUM OF K, CR RNO N CONTENT x SHOOT WT:
Fig.
4.7.
18
20
21
2
(GxG )
The effect of different levels of nitrog~n and calcium on
the relationship' bet~een tplant weight) x (root weight) x
troot weight) ana the ttotal sum of gotassium, calcium and
lU'nltrogen)
x
shoot weight
x tshoot wei ht).
.;full
nutrition +;low-ca cium *;low-nifrogen. Slope an~ confidence
limit
for low-nitrQgen, full nytritiQn, and lsw-calcium
treatments are; O.06JZ±O.054, O.084±O.0042, O.0469± .0112
I-'
W
l.D
16 r-r-
-,------r------ ---
-,------
T-~-------'
+
+
14 I-
~
4=
..
.
* +
+ +
+
• t'
8
I0
0
0:::
6
r
.,.
++
0
0
*
:r:
en
+
++
12 [
0
......
Ia:
"I-
+
++
+ ++
10
n:::
++
*
:[,
'1
2
6
"',**
8
*
'" * '"
10
l/RCTIVITY RRTIO WITH RESPECT TO CR
Fig.
4.8.
*+
*
'" :".. "'*
4
+
+
~'"
*
12
*
14
16
(G/G/ORY)/(G/G/OAY)
The effect of different levels of nitrogen and calcium on
th e
re atlonship'
between the shoot/root ratio and the
reciprocal of activitY ratio with respect to calcium uptake.
.;full nutrition +; ow-calcium *;low-nitrog~n
,.......
..j:::.
0
10 2 X 12£1
110
+
100
N
<.:)
><
+
9£1
+
<.:)
8£1
N"
f3:
70
f-
a
a
a:::
60
x
f-"
3:
5£1
>-
a:::
0
+
':1:£1
+
30
+/+
f-
Z
a:
-.I
(L
20
1£1
£1
0
30 X 10 3
15
20
25
(GxG 2 )
TOTRL CR· CONTENT x SHOOT WT:
4.9. hThe effeGt of different levels of nitroq~n a~d calcium )on
e relatlonship' bet~een tplant we19ht) x troot weight x
root weight ana the tcalcium content) x (shoot wei nt) x
shoot welgh~) • • ;full nutrition +;low-calcium *;low-ni{rOgen.
loge and.cQnfidence limit for low-nitrogen, low-calcium, and
full nutrltlon treatments are1.561±O.139, O.432±O.033, O.297±O.015
10
5
Fig.
I
35
I-'
.+::>
I-'
142
4.3.
Discussion
Central to the hypothesis of Davidson(1969a, 1969b) and
Hunt(1975, 1976), as expressed in the empirical equation 3.2,
is the assumption that the partitioning of dry weight between
the root and shoot of the plant is controlled in inverse
proportion by the relative rates of nutrient absorption and
photosynthesis and it also assumes that the specific root and
shoot activities are solely dependent on their
masses,
respectively.
As previously discussed in Chapter 3, the
results of the present experiments throw serious doubts on
these assumptions.
The good relationship obtained in terms of correlation
coefficients when the data were plotted as shoot/root ratio
against l/activity ratio as shown in Figs.
4.2 and 4.3,
although the form of curve produced was not linear, provides
further evidence that the assumptions made by Davidson(1969a,
1969b) and Hunt(1975, 1976) do not apply with cucumber plant.
While it is acknowledged that the equation 4.4 is the
reciprocal of equation 3.2 in terms of mass ratio, the former
biological
concept.
different
equation is based on a
Davidson(1969a, 1969b) and Hunt(1975, 1976) used the dry
weight of organs as a measure of their functional sizes.
Equation 4.3 assumes that the size of the shoot and root
represents physiological conditions prevailing in the plant
which affects the specific functions of each organ independent
of their mass. The argument is that the form of equation 3.2
does not acknowledge the intimate inter-dependence of the
specific functions of the shoot and root upon each other.
It
is acknowledged that root/shoot ratio used in the equation 3.2
may be biologically significant explaining the dry weight
partitioning once the specific functions of shoot and root are
measured.
However, a serious limitation
lies
in
the
assumption that the entire shoot and root always participate
in their respective photosynthetic and absorption activities,
resulting in the root/shoot ratio.
It can be seen in Fig. 3.45 that the degree of increase
or reduction in the shoot/root ratio was not proportional to
the available light levels. The difference in the shoot/root
143
ratio between full
light and 50% full light treatment was
small while the increase in shoot/root ratio was much higher
under 10% full light treatment, implying that a until certain
light level, the decrease in shoot/root ratio is small.
It
appears, therefore, that there exist critical light levels
which affect the dry weight distribution significantly.
At
the same time, the difference in the values of SAR between
full light and 50% light treatment was negligible whereas 10%
full
light
treatment
increased
the
values
of
SAR
significantly(Fig
3.40).
As
Oavidson(1969a,
1969b),
Hunt(1975,
1976),
Thornley(1976,
1977)
and
Charles-Edwards(1982) admit, equations 3.1 and 3.2
were
empirically derived from the experimental results in the hope
that the effect of particular stress imposed on shoot and/or
root will satisfactorily predict the dry weight partitioning
of shoot and root resulting from their differences in the
specific activities. Hence, the type of curve or line should
explain the response of the plant adequately. In the light of
this argument, it is noted that the form of a curvi-linear
plot shown in Fig. 4.3 rather than a linear plot is a better
representation
of
the dry weight partitioning pattern.
Therefore, it is concluded that the form of the equation which
includes the shoot/root ratio(equation 4.4) represents the
biological response of the plant better than when root/shoot
ratio(equation 3.2) is used.
While the biological significance of equation 4.6 i s
difficult to appreciate, it is interesting to note that the
additional parameters used made little difference compared to
the original equation 3.3 proposed by Thornley(1972). The
values of the correlation coefficient obtained from equation
4.6(r=O.995, Fig. 4.4) is comparable to the one obtained from
equation 3.3(r=0.997, Fig. 3.8), and both equations showed a
single line relationship.
Figures 4.5 and 4.6 also showed
much the same results when compared to Figs. 3.17 and 3.20 in
that significantly graded lines are produced depending on the
ionic strengths of solution(Expts. 4 and 5) rather than light
intensities(Expt.
5). Figure 4.7 also showed that there are
significantly different lines depending on the treatment, a
situation similar to the data shown in Fig. 3.32, indicating
144
I
that there was little difference whichever mass ratio was
used.
However, as discussed in the Chapter 3, the use of SAR
and USR as specific activities of root and shoot
was
responsible for the two line relationship observed. Similarly
the three line relationship based on equation 4.6 as shown in
Fig.
4.9 was not different to that achieved using equation
3.3(Fig. 3.26). Hence, there is no more justification for
accep~ing
the assumptions contained in the equations used by
Davidson(1969a, 1969b) or Hunt(1975, 1976) than there is
accepting the demand concept which is the basis of equations
4.3 and 4.4.
There is considerable evidence to support the suggestion
that the activity of source is closely related to the demand
of sink. Tollenaar and Daynard(1982) showed that a delicate
balance
existed
between
source
and
sink during the
grain-filling period of maize.
In
soybean,
treatments
altering source/sink ratio such as. partial defoliation and
shading also alter the rates of photosynthesis (Alderfer and
Eagles, 1976;
Fellows et al, 1979; Peet and Kramer, 1980;
Thorne and Koller, 1974).
Wardlaw and Moncur(1976) also
showed
that there is a close relationship between the
requirement for assimilates by the ear of wheat and speed of
their movement through the peduncle to the ear. However, in
the case of shoot and root relationships, it is difficult to
define source and sink because they can both act as source and
sink at the same time.
Viewing whole plants in terms of
source-sink
relationships,
the
equality of the source
strength(production
of
assimilates)
and
sink
strength(utilization of assimilates) is only justifiable if
the
proportion
of
assimilates
stored
is
negligible(Warren-Wilson, 1972). This fact is compatible with
the assumption made by Hunt and Burnett(1973) and Hunt(1975)
that equation 3.2 is applicable to young plants which have
little storage material.
In the context of a balanced
source-sink relationship, Davidson's(1969a, 1969b) hypothesis
shown in equation 3.1 is only applicable when the entire shoot
and
root
are
presumed
to
actively
participate
in
photosynthesis and absorption and negligible shoot or root dry
weight is in a stored form.
The concept that the driving force for the absorption of
ions at the root surface is created by the growth of plants,
as claim~d by Nye and Tinker(1969) and supported by other
authors (Fitter and Hay, 1981; Pitman, 1972; Woodhouse et
al, 1978) basically contradicts Davidson's(1969a,
1969b)
hypothesis because the form of equation 3.1 does not take into
account the integrated response of the plant.
Clarkson(1982)
presented evidence that the nutrient uptake is closely related
to the rate of growth and suggested that metabolic or growth
demand regulates the rate of nutrient uptake. Therefore, it
is argued that Davidson's (1969a, 1969b) hypothesis expressed
in terms of equation 3.1 supported by others such as Hunt and
Burnett(1973),
Hunt(1975,
1976),
Thornley(1972,
1982),
Charles-Edwards (1982), Richards(1977, 1981) and Richards et
al(1979) may require further examination in the light of the
following conclusions from the present studies before it can
be accepted as a generalized equation for
non-seedling
cucumber plants.
First, the specific activities of shoot and root did not
follow
the
predictions
that
Hunt(1975) and Hunt and
Burnett(1973) made. Instead, specific activities of an organ
were more closely related to the physiological conditions of
the opposite organ whose function was under stress
as
discussed in Chapter 3.
Secondly, it was equally valid to use shoot/root ratio as it
was to use root/shoot ratio to describe the functional
relationship between roots and shoot. Therefore, dry weight
partitioning between shoot and root did not follow the
predictions Hunt(1975) and Hunt and Burnett(1973) made.
5 showed
The experimental results obtained from Expt.
t~at
the lack of light in the shoot environment resulted in a
high shoot/root ratio(Fig.
3.45) and this physiological
indication of the plant was revealed as high demand for the
nutrients, which was reflected in high specific function of
root expressed as SAR(Fig.
3.40).
Cumbus and Nye(1982)
concluded that the effect of low solution temperature was to
lower the demand of the shoot controlling the nitrate uptake
and that the slow growth rate of rape(Brassica napus L.) at
low temperature was not due to the shortage of nitrogen in the
14b
shoots. It is interesting to note that environmental stresses
affect the root absorption activity through the demand of the
shoot, high demand by low light intensity in the present study
and low demand by low solution temperature in the study of
Cumbus and Nye(1982). It is appreciated that the specific
functions of shoot and root are closely related to the
physiological conditions of the opposite organ, but it may be
an over-simplification to suggest that the weight of an organ
controls the specific functions in the opposite organ, which
is the basic concept contained in equations 4.4 and 4.6.
Walker and Ho(1977) showed that the concentration of sucrose
in the tomato fruit determines the rate and direction of
translocation of carbon assimilates, implying
that
the
response of source activity may be specifically met by sink
demand. Results obtained by Lee(1982) confirm this view.
He
showed that barley plants grown under a short supply of
phosphorus, sulphur, chlorine and nitrogen absorbed these
nutrients rapidly and was ion-specific when these nutrients
were supplied in the solution. However, even though the use
of weight of the opposite organ controlling the sink demand in
the present studies is not specific terms, such as relative
growth rate of shoot(Pitman, 1972) and the concentration of
sucrose in the tomato fruit(Walker and Ho, 1977), it may
represent the basis of inter-dependence of shoot and root by
multiplying the size of opposite
organ
with
specific
activities.
As emphasized in the previous Chapter, the inclusion of
shoot and root morphological terms in equation 3.5 is based on
empirical observation at this stage, but it contains a
biologically meaningful concept in a way that Hunt(1975, 1976)
and Thornley's(1972) equation does not.
The
biological
significance of equation 3.5 is in the use of the ratio of
morphological terms as a description
of plant response.
Therefore, single line relationship obtained from area or
number terms that has been the basis of
morphological
inter-relationship between shoot and root(Figs. 3.63-3.68) is
not to be cancelled out from the equation 3.5.
The proposal
put forward was that that root length is more closely related
to leaf number than leaf area in certain environments.
The
.I. '"t I
inclusion of morphological terms in equation 3.5 implies an
integrated response of plants as shown in equation 4.3.
The
pOint is that if an equilibrium exists as represented by
equation 3.5, then the following equation may be derived,
plant wt. x (root no./root length) a "k" x (leaf no./leaf
area)
This form of equation resembles equation 4.3 in the sense that
total activities of shoot and root are related to the
morphology of the opposite organ.
This may have been the
reason why equation 3.5 represented a better functional
relationship between shoot and root than equations 3.2 and
3•3 •
The fact that plants grown in the low-calcium treatment
did not show deficiency symptoms and that none of the
established
an
equilibrium
satisfactorily
equations
relationship with respect to calcium uptake when different
levels of calcium were applied requires some explanation.
In
view of the result obtained by Bengtsson and Jensen(1982), who
showed that cucumber plants grown within the range
of
O.3mM-2.0mM of calcium showed no difference in growth, the
O.3mM concentration used in the low-calcium treatment in the
present study may have been sufficient for normal growth. In
addition, it is well known that the nutrient requirements for
shoot growth in flowing solution culture are much lower than
static conventional growing systems. For example, Loneragan
et al(1968) found that some legumes and herbs grew much better
at low concentration of calcium(2.5 and lOuM) than many
Gramineae, which contradicted results obtained in standard
nutrient culture techniques.
The fact that the calcium
concentration
in
shoots
remained constant while yield
increased substantially led Loneragan and Snowball(1969a) to
propose
the
term "functional nutrient requirement
and
indicated that the minimal functional requirement of the shoot
for calcium is low when flowing culture techniques were used.
It is probable that rates of depletion of essential elements
in conventional solution culture may be rapid, as Asner(1978)
pointed out, whereas, in a continuously flowing solution
culture systems, the depletion of elements is minimized.
Loneragan and Snowball(1969b) concluded that rates of calcium
ll
148
absorption by legumes and herbs were high and this fact
enabled those species to offset their high tissue requirements
for calcium when they were grown in the flowing solution
culture. If this is the case with cucumber plant it is
probable that the continuous supply of a low concentration of
calcium may meet the functional requirement of shoot, and not
limit the growth of shoot.
In this case, the dry weight
production used in representing the functional equilibrium
relationship as in equation 3.2 would not be expected to show
a linear relationship since these equations imply that the
growth of a plant is the function of ion concentration of root
medium due to the assumption that nutrient uptake is the
function of available root mass. Clarkson(1979) argued that
the shoot controls the absorption of calcium because of the
fact that the shoots under environmental stress develop
calcium deficiency symptoms quickly, regardless of calcium
status of the root medium. This suggests that the uptake of
any elements may be closely related to the demand of the
shoot. The form of equations 3.1 and 3.2 can not explain such
an integrated physiological response because the specific
absorpti~n
rate in the equation, which is the amount of
element taken up per root weight per unit time, simply implies
that the absorption of element is the function of root weight
and external concentration of root medium.
As discussed in
Chapter 3, the absorption activity of the root was markedly
increased when the shoot was under stress (Fig.
3.40), and
this clearly demonstrated the integrated response of plants,
emphasizing the importance of physiological demand of shoot.
Pitman(1972) derived the empirical equation,
Uptake
= function(concentration, growth)
the point being that the uptake of elements not only depends
on the external concentration but also growth of plant, the
concept which is the basis of equation 4.3.
Clarkson(1982)
questioned the view that the transport system in the plant has
a constant affinity for specific ions on the basis that the
physiological demand for specific ions may far exceed that
maximum capacity.
1'+:1
The observations that plants grown using Nutrient Film
Technique(Cooper, 1975) grow well at less than the optimal
nutrient range of static solution culture(Winsor, 1978) is in
agreement with Loneragan and Snowball 's(1969b) work despite
the different ions studied. Nitrogen levels required in the
flowing solution cult~re are also low. Clement et al (1978)
found that maximum yield of ryegrass in flow solution culture
was obtained at 1400uM N0 , but surprisingly yields measured
3
in terms of total plant dry weight were reduced to only 90%
and 70% of the maximum at concentration of 14uM and 1.4uM N0 ,
3
respectively. The nitrogen concentration of approximately
4mg/litre used in Expt. 6 was considerably less than that of
Winsor ' s(1978) work, who showed that
plants
grown
in
circulating nutrient solution showed little difference in
growth over a
wide
range
of
nitrogen
levels
from
10-320mg/litre. Cooper and Thornley(1976) made no distinction
on the validity of using equation 3.3 even though the tomato they
examined were grown in NFT system. These plants have a high
proportion of stem in the shoot weight similar to cucumber,
and the plants were grown in different solution temperatures.
As shown in the Figs. 3.5-3.8 and 3.14 , there existed a good
linear relationship with equation 3.3 when cucumber plants
were treated with different solution temperatures while other
treatments
such as different ionic strengths and light
intensities showed Significantly graded lines(Figs. ·3.17,
3.20, 3.26, and 3~29).
Hunt and Burnett(1973) showed that
there exists a tolerable relationship between root/shoot ratio
and the l/activity ratio under the different light levels when
perennial ryegrass was grown in the soil, not the flowing
solution culture system. The present experiment also showed a
tolerable relationship despite the different technique of the
growing plants, while other stresses such as low solution
temperature, and low levels of nitrogen and calcium did not
show a good relationship. It is suggested, therefore, that
the different techniques of growing plants need
to be
carefully defined when discussing the existence of functional
equilibrium equations concerning shoot and root activities.
l~U
In conclusion, the experimental results shown in this
Chapter concerning dry weight partitioning and in the previous
Chapter concerning the response of specific activities of
shoot and root, indicate that equation 4.3 represents a better
relationship between shoot and root in discussing functional
equilibrium.
Equation 3.5 incorporates the morphological
arrangement of shoot and root and the possible effects of
their
morphological
arrangement
on functions with the
exception of calcium uptake better than any other equations
tested.
The fact that none of the equations used in the
Chapters 3 and 4 satisfactorily established a relationship for
uptake may be due to the low-calcium requirement of the shoot
when plants were grown in flowing solution culture.
151
CHAPTER 5
AGRONOMIC IMPLICATIONS
One of the main physical characteristics of the NFT
of growing plants is the shallow depth of the
system
circulating nutrient solution. Unlike plants grown in soil or
in conventional hydroponics the proportion of the root system
immersed in the solution becomes progressively smaller with
time, and conversely a higher proportion becomes exposed to
the air. This characteristic of plants grown in NFT would be
expected to be accentuated where the physical dimensions of
the troughs and the growth of competing plants confines the
volumes of solution available to each plant grown in the
system. It would be expected therefore that the depth of
solution would affect the proportion of the root system
directly involved in the absorption of water and mineral ions.
One of the objectives of the series of experiments
reported in this thesis was to investigate the effect of
solution depth on the growth of cucumber plant grown in a
circulating nutrient solution in which solution depth could be
controlled more precisely than the commercial system developed
by Cooper(1975).
The cucumber plant used in the present experiments was
ideal for this type ~f study as the growth rate of the shoot
and root was high; 5m of leaf area, 10km of root length and
a total plant dry weight of 400g was achieved in two months.
Therefore the depth effects on plant growth
could
be
established rapidly. In addition Graves(1983) suggested that
some of the difficulties experienced in growing cucumber in
NFT might be due to its fast growth rate. However the
literature does not reveal any work which attempts to examine
the effects of solution depth or how it might contribute to
the poor performances of cucumber under this system.
Experiments 1, 3 and 4 were particularly concerned with
solution depth and its interaction with solution temperature
and nutrient status. The solutions were diluted rather than
being preferentially deficient in a particular element to
simulate t.he variation associated with periodic nutrient
solution
adjustments
might
be expected i n NFL
that
Temperature treatment such as 12.5'C(Expt. 3 , Table 3. 1 ) and
4 ) substantially
5 and 2% f u 1 1 strength solution(Expt.
reduced root growth in absolute terms. Hence the response of
the plant to different solution depths under these treatments
was not as clear' as at higher temperature and nutrient
concentrations where the rates of plant growth were faster and
roots occupied the available solution volume more rapidly.
Results from Expt. 1 show that shoot growth of the
cucumber plants decreased progressively with solution depths
less than 50mm(Fig. 3.42) even though they did not show any
visible signs of nutrient or water deficiency. The reduced
shoot dry weight was accompanied by an increase in root dry
weight(Fig.
3.42) and root number per centimeter of root
length(Fig. 3.47). The overall growth of plants grown in the
50mm(Fig. 3.42) depth however was only slightly less than the
170mm depth treatment for the first 21 days of treatment
during which time the root systems were fully submerged and
had not fully exploited the solution space available in the
container.
The marked reduction of shoot growth resulting
from solution depths less than 50mm suggests that the normal
shallow depths of solution used in the NFT system may not be
sufficient to maintain maximum shoot growth rates of cucumber
plants.
There are several possible reasons for the reduced
shoot growth. A large part of the root system in the shallow
solutions
was above the nutrient solution and did not
participate in the absorption of nutrients and water, implying
that better cucumber plant growth is achieved when more of the
root system is submerged in the solution.
However the fact
that the growth of the plant was only marginally improved by
increasing the depth from 50mm to 170mm indicates that
complete submergence may not be necessary. If it is assumed
that when the root system of the plant fully occupies the
solution volume available to it all the roots in the solution
are oriented vertically the results would indicate that the
effective part of the root is within 50mm of the root tip.
Solution depths less than 50mm would therefore not allow the
plant to completely utilize the potentially most active part
153
of the root system although dry weight resources of the plant
were committed to the root at the expense of shoot growth.
While authors such as Winsor and Massey(1978) attribute the
failure of cucumber plants in NFT to disease it is highly
likely that the difficulties of growing cucumber plants in
this system may in part be due to the shallow solutions used.
The results obtained in the present experiments support
Cooper's(1979) proposal that the exposed roots do have a
function other than mineral and water uptake(see Appendix 3).
He
proposed that this function was involved in oxygen
absorption. While it is well known that oxygen availability
affects plant growth, there is ample evidence to suggest that
the root controls shoot growth through hormones produced in
the root tips(Chibnall, 1954; Phillips, 1964; Went, 1943).
McDavid et al(1973)
showed
that
the
application
of
6-benzylaminopurine to the shoot of peas(fisum sativum L.)
compensated for root removal and suggested that the supply of
cytokinins
from
the root may affect leaf function by
maintaining the photosynthetic activity of the leaves. In the
present study, chlorosis of the leaves of plants grown in low
solution temperature recovered when some roots were grown
above the solution(see Appendix 3) supporting the findings of
Went(1943) and McDavid et a1(1973).
The data from Expts. 2 and 3 showed that the critical
root
temperature
below which cucumber plants exhibited
abnormal leaf chlorosis lies between 15 and 20'C(Appendix 3
and Table 3.1).
This agrees with the recommendation that
cucumber plants should not be grown with their roots below
l8'C under glasshouse condition (Calvert, 1956;
Cooper,
1973).
A number of suggestions have been proposed to explain the
effect of low root temperature on plant growth. Power et
a 1 (1970), 0 s mo n d and Raper(1981) and Davis and Lingle(1961)
attributed the slow initial growth rate of the shoot at low
soil temperature to reduced nutrient translocation from root
to the shoot rather than a reduced rate of nutrient uptake.
Atkin et al(1973) suggested that low solution temperatures
the balance of growth promoters and inhibitors
altered
154
exported from the root. The present study showed that the low
temperature
markedly
reduced root length extension and
increased the relative number of root initials(Fig.
3.48).
This is in agreement with the conclusions of Cumbus and
Nye(1982) who showed that the slow growth rate of rape was not
associated with a shortage of nitrogen in the shoots but with
the root morphology and carbohydrate availability to the root
meristems.
~Low
solution temperature influenced the shoot morphology
by producing plants with few leaves and small individual leaf
areas. However the production of new leaves was relatively
less affected than leaf area as discussed in Chapter 3. This
supports the suggestion by Richards and Rowe(1977a, 1977b) and
Chung et al (1982) that a close relationship exists between
root length and leaf area, and root number and leaf number.
The relationship between root number and leaf number may be
mediated through hormone synthesis in the root tip(Atkin et
al, 1973; Barlass and Skene, 1980; Skene, 1975) influencing
the differentiation of new leaves in the shoot. Whatever the
reason the fact that low temperature restricts root length
extension would certainly limit the plants ability to exploit
the
nutrient
and
water resources of the root medium
particularly if the plants were grown in soil.
It is also
suggested that the presence of aerial roots, if they are
growing at a more favourable temperature than those which are
submerged may partially overcome some of the detrimental
effect of low solution temperatures by maintaining
the
photosynthetic activity of those leaves(Appendix 3) which are
produced and provide an alternative hormonal explanation for
the importance of the above solution part of the root system
in the NFT system than oxygen absorption as suggested by
Cooper(l979) •
The plant response o,btained from experiments 4,5 and 6
indicates that nutrient levels in the solution influence the
allocation of dry weight(Figs. 3.44-3.46) and morphology of
the root system(Figs.
3.49 and 3.50). At low strength of
nutrient solution the shoot/root ratio decreased and the root
system becomes more elongated and relatively less branched.
The fact that solutions where only the nitrogen concentration
155
was reduced produced a similar effect as when the total
solution is diluted(Fig. 3.44-3.46) indicates that it is the
nitrogen level which has the major effect. These results
agree with the work of Hegarty(1973) who showed that Sitka
spruce[£._ic_~~ ~i!£h._~!!~.!~ (Bong) Carriere] seedlings had a much
lower shoot/root ratio and higher absorbing surface area
ratio(root length/leaf area) in dilute solution than in
control solutions. This type of growth of the root system
where nitrogen deficiency stimulates the exploratory form of
the root has also been reported for tomato(Winsor and Massey,
1978) and for orchard and bromegrass(Bromus inermis Leyss.)
(Oswalt et al, 1959). In the present study calcium deficiency
did not produce a stimulatory response in the root although
Bengtsson and Jensen(1982) in their
work
showed
that
shoot/root ratio of cucumber was the lowest when the calcium
concentration was as low as O.lmM.
The results did not show
however that levels of nutrients stimulated branching of the
root system similarly to the 1I1 0ca lized stimulatory growth ll as
reported by Drew(1975) and Hackett(1972) for cereal and Coutts
and Philipson(1976) for trees while the lack of nitrogen
induced IItotal stimulatory growth
From this it could be
concluded that the root system when confronted with
a
localized abundance of nutrients takes on an exploitive form
by becoming more branched and an elongated less branched
explorative form when nitrogen is deficient. Although not
examined in the present series of experiments other authors
have indicated that phosphorus deficiency might also show a
similar response(Drew, 1975;
Hackett, 1972) whereas iron
stress causes increases in lateral root formation in sunflower
(Rdmheld and Marschner; 1981a, 1981b) and in tomato(Brown and
Ambler, 1974). Drew(1976) pointed out that plants are able to
explore the soil only when it is not starved of nutrients. He
makes a subtle distinction between starvation and deficiency.
As the nitrogen level in the experiments 4, 5 and 6 was
4mg/litre it seems that the plant as a whole was nitrogen
deficient rather than starved, at least during the early
stages of growth. As shown by Oswalt et al (1959) with grasses
nitrogen deficiency may stimulate the root to grow deeper than
in a nitrogen rich environment.
This may be a useful
adaptation mechanism in cucumber plant survival and may be
ll
•
156
exploited agronomically where it is desirable to encourage
deeper root growth to tap a more reliable source of soil
moisture at depth in periods of short term drought.
The data from experiments where cucumber plants were
subjected to varirrus levels of nutrient concentration and
light intensities simultaneously(Expt.
5)
produced
an
interesting
insight
into
the competitive dominance of
different environmental stresses in the adaptive strategies
adopted by cucumber plants. Considering the major reduction
in total plant growth resulting from
50%
full
light
treatments, it was surprising to observe that the partitioning
of dry weight between the shoot and root was still dominated
by the ionic strength of the solution. It can be implied that
the effect of low light intensity on the leaf area of cucumber
plant was mediated through the root. Lowering the light intensity
to 10% of full light caused plants to become taller, less
branched and leaves were thinner compared to higher light
intensity treated plants.
These results agree with the
findings of Causton and Venus(1981). The proportion of leaf
area to the whole plant growth(leaf area ratio) in low light
was greater than in high light intensity treatments. It would
appear that a shift of the plant to a low light morphological
form only occurs fully when the light intensity is extremely
low. Not only is the shoot morphology affected when that
point is reached but root morpho1ogy(Fig. 3.49) and root
absorption activity(SAR, Fig.
3.40) also change.
It was
noted that the leaf colour of the plants grown in 10% full
light was much greener than in full light treatment even when
plants were grown in 5% full strength nutrient solution.
Analysis of K, Ca and N in the leaves showed a comparable
percentage
to
that achieved in full strength nutrient
solution.
Lowering light intensities to 10% full light
intensity caused the root number/root length ratio to be
higher than other treatments(Fig.
3.49).
The response of
cucumber
plants to low intensity involves two adaptive
strategies. The first involves a change in the structural
morphology of the shoot and root and secondly an enhancement
of the photosynthetic efficiency of the leaves and the
absorption of the root. It is possible that the latter is a
1~ I
function of the former. The clear cut influence of light is
somewhat confused when the light intensity is only moderately
reduced and as shown in 50% full light treatments a strong
interaction of light intensity and nutritional levels in the
solution exist. It could be speculated that under poor light
conditions which often occur in winter that high nutrient
levels are essential if the maximum shoot growth is to be
achieved under the prevailing light levels available. This
may explain the observations made by some workers that the
uptake
of
nutrients is closely related to the aerial
environments(Adams, 1981; Adams and Winsor, 1979; Adams and
Grimmett, 1981) and it is suggested that the different
nutrient concentrations may be required to successfully grow
plants in NFT during the winter and summer.
158
CONCLUSIONS
The series of experiments reported in this thesis were
primarily concerned with the dry weight partitioning and
morphological adaptation of cucumber roots influenced by
various environmental stresses and its consequences on the
shoot morphology. All the data were utilized to determine
whether the functional equilibrium equations proposed by
Davidson{1969a, 1969b), Hunt{1975, 1976) and Thornley(1972)
adequately represented the plant behaviour under a wide range
of environmental stresses.
The following are the major conclusions
studies.
drawn
from
the
1. The root system responded to different environmental
stresses in different ways.
Lowering solution temperature
enhanced the production of root number relative to root length
whereas lowering ionic strength and nitrogen levels of the
solution favoured the preferential growth of root length.
While the increase in the number or length of roots may be
associated with the increase in root weight, the importance of
morphological changes of root system can not be overlooked.
It is argued that morphological adaptation of roots is more
important in root function than root mass alone.
2. The close coordination between shoot and root was
revealed in morphological terms such as root length and leaf}
area, and root number and leaf number. The extension of root
length was achieved at the expense of leaf area growth when
low ionic strength or low-nitrogen levels in the solution were
applied.
Lowering
solution
temperature
enhanced
the
production of root number and this was revealed in the
uninterrupted
production
of leaf number in the shoot.
Shoot/root mass ratio used conventionally to. represent the
relationship between shoot and root does not describe this
relationship adequately and oversimplifies
the
adaptive
strategies available to plants to overcome environmental
stress.
159
3. Equation 3.2 assumes that the entire shoot and root
participate in their specific activities(USR and SAR). The
present studies showed that the presence of stem can be a
significant factqr in the adaptation of the plants. The
proportion of dry weight allocated to the stem and leaf was
different
depending
on
the
stress
applied
and was
complementary. Hence it is suggested that the use of equation
3.2 with stemmy plants may be justifiable only in some
situations such as when nutrient stress is applied.
4. The fundamental limitation of equation 3.2 appears to
lie in the use of weight terms as determinations of the
functional size of shoot and root.
Sensitive morphological
changes in response to environmental stresses are ignored in
this equation. In addition, the concept of plant demand which
is a "driving force" at the root surface is not considered in
the equation 3.2.
The present studies revealed that the
specific activities of shoot and root were closely related to
the physiological conditions of the opposite organ.
For
example, SAR of root was markedly increased when shoot was
under light stress and the USR was also increased in response
to nitrogen stress. The empirical equations used in Chapter
4, which included the demand concept did not improve the
relationships mathematically but are as acceptable as those
which were based on the concept that activity of an organ was
solely a product of its mass, as in equation 3.2.
5. Although equation 3.5 is empirical, it does include
the demand concept and morphological terms and as such
represented a wider range of plant adaptation strategies to
overcome various shoot and root stresses. The noticeable
exception is calcium stress.
Clarkson(1979) suggested that
calcium absorption is a function of the demand in the shoot.
Further work is required to understand the nature of this
demand as it appears to be independent of morphological
changes which occur in the plant.
160
ACKNOWLEDGEMENTS
I would like to acknowledge the help and contributions of
many people and organizations in Korea and New Zealand,
without whose assistance this project could never have been
completed.
I am particularly indebted to my supervisors, Professor
R.N.
Rowe and Dr R.J. Field for their encouragement. They
have been extremely patient and understanding through all my
shortcomings.
I am grateful to the Colombo Plan under the joint
assistance of the Republic of Korea and New Zealand, and
particularly to the Agricultural College, Chonnam National
University of Korea.
Messrs G. Steans, B. Smith and M.
Spurway provided
much of the needed assistance in technique and glasshouse
work. Mr R. Edwards helped proof-read parts of this thesis.
Mr C.
Booth and his family was always close to my family
while we stayed in Christchurch.
I am immensely indebted to my parents-in-law, my parents
and my relatives for their love and support. Finally, to my
wife, Soomi and children, Ki Wi and Ki Ung for their love,
patience and understanding and I dedicate this work to them.
101
REFERENCES
ADAMS, P. 1981. Nutrient uptake. Glas~~~use ~rops Research
Ins ! i_t.tl~ ~!l_~l ~r.1 liZi p. 85 •
ADAMS, P.;
GRIMMETT,
M.M.
1981.
Nutrient
uptake.
lia~~~_QLI?~
~rQ22.
~es ear.~
Ins tit u te An nu a 1 ~ort 1980
p.52-53.
ADAMS, P.; WINSOR, G.W. 1979. Nutrient uptake.
Glasshouse
f-,=-~p.?. ~~?.earc!l ~~ti~~!~ Annual Report 11~ p.84-85.
ALDERFER, R,G.; EAGLES, C.F. 1976. The effect of partial
defoliation on the growth and photosynthetic efficiency
of bean leaves. Botanical Gazette 137: 351-355.
ANDREWS, R.E.; NEWMAN, E.I. 1968.
The influence of root
pruning on the growth and transpiration of wheat under
different soil moisture conditions. The New Phytologist
67: 617-630.
ASHER, C.J. 1978. Natural and synthetic culture media for
Spermatophytes, p.575-609. IN: Rechcigl, M.Jr. Culture
~edia ~q~ microorganisms and plants.
V.III. Section G:
Qiet...?., culture media, and food supplements. Ohio: CRC
pre s s.
ATKIN, R.K.; BARTON, G.E.; ROBINSON, O.K. 1973. Effect of
root-growing temperature on growth substances in xylem
exudate of zea mays. Journal of Experimental Botany 24:
475-487.
AUSTIN, R.B.; FORD, M.A.; EDRICH, J.A.; HOOPER, B.E. 1976.
Some effects of leaf posture on photosynthesis and yield
in wheat. ~nn~l.?. Qf ~PQli~i ~Q~ 83: 425-446.
BARLASS, M.; SKENE, K.G.M. 1980. Studies on the fragmented
shoot apex of grapevine. II. Factors affecting growth
Journal of Experimental
and differentiation in vitro.
Bot~ 11:
489-495.
BARBER, S.A. 1979.
Growth requirements for nutrients in
relation to demand at the root surface, p.5-20. In:
Ha r 1 ey, J. L • ;
Russell, R.S.
The soil-root
- - - - interface.
London: Academic Press.
BAZZAZ, F.A.; HARPER, J.L. 1977.
Demographic analysis of
the growth of ~inum usitatissimum. The New Phytologist
78: 193-208.
!
lOt:
BENGTSSON, B.; JENS~N, P. 1982. Uptake of calcium in wheat
and cucumber roots. fhys(Q.1Q.gj~ P-1.9_llt~rJcJE. ?5: .273-278.
BG8TE, K.J. 1977. Root:shoot relationships. Soil and ~~~
~£J ~nc:~ ~()c:j~~J~_ .Qi D Qr.L~ ~:
15 - 23.
BOSEMARK, N.O. 1954.
The influence of nitrogen on root
d eve lop men t • fhy~t~l.Q.RL~ P1 ant a rum I: 4 9 7- 5 0 2 •
BROUWER, R.
1977.
Root functioning, p.
229-245.
In:
Landsberg, J.J.; Cutting, C.V. Environmental effects on
£r.oQ ~~l~iolQ_~' London: Academic press.
BROUWER, R. 1981. Co-ordination of growth phenomena within a
root system of intact maize plants. Plant and Soil 63:
65-72.
BROWN, J.C.; AMBLER, J.E.
1974.
Iron-stress response in
Sites of Fe
tomato(~ycQP~!~~~~
~culentum).
1.
reduction,
absorption
and
transport.
Physiologia
Plantarum
31: 221-224.
--.
--_._- --- CALVERT, A. 1956. The influence of soil and air temperatures
on
cropping
of
glasshouse
tomatoes.
Journal of
Horticultural Science 31: 69-75.
CAUSTON, D.R. 1969.
A computer program for fitting the
Richards function. Biometrics~: 401-409.
CAUSTON, D.R.; VENUS, J.C.
1981.
The biometry of plant
London: Edward Arnold. 307p •
.9.r..~w t h.
CAUSTON, D.R.; ELIAS, C.O.; HADLEY, P.
1978.
Biometrical
studies of plant growth. I. The Richards function, and
its application in analysing the effects of temperature
on leaf growth. Planl and Cell Environment 1: 163-184.
CHARLES-EDWARDS, D.A. 1976. Shoot and root activities during
steady-state
plant
growth.
Annals of Bota~ ~:
767-772.
CHARLES-EDWARDS,
D.A.
1982.
Dry-matter
partitioning,
p.87-112.
In:
Physiological determinants of .~
i~?!t~.
Sydney: Academic Press.
CHIBNALL, A.C.
1954.
Protein
metabolism
in
rooted
runner-bean leaves. I~ New Phytologist ~: 31-37.
CHUNG, G.C.; ROWE, R.N.; FIELD, R.J.
1982.
Relationship
between
shoot
and roots of cucumber plants under
nutritional stress. Annals of Botany ~: 859-861~
CLARKSON, D.T. 1979. Sites of calcium transport in roots and
their dependence on metabolism. ~our'l.<!191. t.~ ~~i~nce
Qr f....<?_ oQ. ~n Q. ~g r .i~_~Lt_~Te lQ.: 747 •
CLARKSON,
D.T.
1981.
Phosphate
transport
in
phosphate-stressed tomato plants. ~~cultural ~esearch
~~U!!cJl h..~~~Q.mb~ h..~.~~~~~9IL ~!!.nual
Report 1980 p.58-60.
CLARKSON, D.T. 1982. Nutrient demand as the pacemaker for
nutrient absorption and root development, p.1-14~:
Shot ton, F• E•
~~rt.?.
a f ~ grow t h ( Pro c •
A0 AS
Conference, Bournemouth, 1981). MAFF Reference book 341,
HMSO, London
CLARKSON, D.T.;
GERLOFF, G.C.
1979.
The
effects
of
temperature on root growth and mineral nutrition of young
maize plants.
Agricultural Research Council Letcombe
h~bor~~Qry Annual Report 1978 p.52-54.
CLEMENT, C.R.;
HOPPER, M.J.;
JONES, L.H.P.
1978.
The
uptake of nitrate by Lolium ~renne from flowing nutrient
solution. I. Effect of N0 concentration.
Journal of
3
~p ~j_~~!!~_~ ~.t_~!!,t 29:
453 - 464.
COOPER, A.J. 1971. The effect of root pruning on the growth
of tomato plants. Journal of Horticultural Science 46:
111-114.
COOPER, A.J.
1973.
Root temperature and plant growth.
Research
Review
No.4.
Commonwealth
Bureau
of
Horticulture and Plantation Crops. 73p.
COOPER, A.J. 1975. Crop production in recirculating nutrient
solution. Scientia
- - - - - Horticulturae 3: 251-258.
COOPER, A.J. 1979. The ABC of NFT. Nutrient film techni~~.
The worlQ.l.?. fi~~l method Q.f ~ production without ~
~Ql'!~ r~.Qtin.9. medium.
London: Grower Books. 181p.
COOPER, A.J.; THORNLEY, J.H.M. 1976. Response of dry matter
partitioning, growth, and carbon and nitrogen levels in
the tomato plant to changes in
root
temperature:
experiment and theory. Annals of Botany~: 1139-1152.
COUTTS, M.P.;
PHILIPSON, J.J.
1976.
The influence of
mineral nutrition on the root development of trees. I.
The growth of sitka spruce with divided root systems.
i~u rn.i!l Q!. t.~p e!jJT!~_nt a 1 ~~~:
1102-1111.
164
CRAM, W.J.; LATIES, G.G. 1971. The use of short-term and
quasi-steady
influx
in
estimating plasmalemma and
tonoplast influx in barley root cells at various external
and internal chloride concentrations. Australian ~ournal
Qi ~QL2..g.L<:~1 Sc i.e nc_~ £±: 633- 646.
CRAM, W.J.; PITMAN, M.G. 1972. The action of abscisic acid
on ion uptake and water flow in plant roots. Australian
Qi Bi ~ Lo gJ<:Al i.~ t~n..~e2 ~: 1125- 1132.
CUMBUS, I.P.; NYE, P.H. 1982. Root zone temperature effects
on growth and nitrate absorption in Rape(Brassica napus
CV Emerald).
~ournal
of
Experimental
Botany
33:
1138-1146.
DAVIDSON, R.L.
1969a.
Effect of root/leaf
temperatu re
differentials
on root/shoot ratios in some pasture
grasses and clover. Annals of Botany~: 561-569.
DAVIDSON, R.L. 1969b. Effect of soil nutrients and moisture
on root/shoot ratios in Lolium perenne L. and Trifolium
rep e n2. L. Anl].~~ Qi. B0~!Jl. ~: 57 1 - 57 7 •
DAVIS, R.M.; LINGLE, J.C. 1961. Basis of shoot response to
root
temperature
in tomato.
Plant Physiology 36:
153-162.
DENNETT, M.D.; ELSTON, J.; MILFORD, J.R. 1979. The effect
of temperature on the growth of indivi.dual' leaves of
Vicia faba L.
in the field.
Annals of Botany 43:
197-208.
DHILLON, S.S. 1978. Influence of varied phosphorus supply on
growth and xylem sap cytokinin level of Sycamore(Platanus
Q~ci.9~.!!.!~_li~
L.)
seedlings.
Plant
Physiology
61:
521-524.
DOBBEN, W.H. VAN. 1962. Influence of temperature and light
conditions on dry-matter distribution, development rate
and yield in arable crops.
Netherland Journal
of
~grl~~ltu~~ ~ience~:
377-389.
DREW, M.C. 1975. Comparision of the effects of a localized
supply of phosphate, nitrate, ammonium and potassium on
the growth of the seminal root system, and the shoot, in
bar 1 e y • I~ New ~hY t 0 1Q!Li s t 12 : 47 9 - 490 •
~Qur_~_a.l
1976.
The effect of the supply of mi neral
DREW, M.e.
nutrients on root morphology, nutrient uptake, and shoot
grow t h inc ere a 1 s •
A.9.i.i c u l1.~__~<!.l ~~~~I_~ Counci 1
h~ t ~_Q~~P~ h~ b0 I~~QI,t Ann u <!.l Re~ 1 9 7 5 p. 63 - 73 •
DREW, M.C.; SAKER, L.R.
1975.
Nutrient supply and the
growth of the seminal root system in barley.
II.
Localized, compensatory increases in lateral root growth
and rates of nitrate uptake when nitrate supply is
restricted to only part of the root system.
Journal of
I..~p ~r:j_ m~!!!.~l ~~ t ~_!!l 2.6:
79 - 90 •
DREW, M.C.; SAKER, L.R.
1978.
Nutrient supply and the
growth of the seminal root system in barley. III.
Compensatory increases in growth of lateral roots, and in
rates of phosphate uptake, in response to a localized
supply of phosphate. Journal of Experimental ~otan~ 29:
435-451EVANS, G.C. 1972. The 9J:!_~!!tiJative analysis Qf. plant growth.
Oxford: Blackwell Scientific Publications. 734p.
EVANS, P.S. 1970. Root growth of Lolium perenne L.
1.
Effect
of
plant
age,
seed weight, and nutrient
concentration on root weight, length, and number of
apices. ~ew Zealand Journal of Botany~: 344-356.
EVANS, P.S.
1977.
Comparative root morphology of some
pasture grasses and clovers.
New Zealand Journal of
A9J:icu_l!ur~ Re.?_earch~:
331-335.
1979.
FELLOWS, R.J.;
EGLI, D.B.;
LEGGETT, J • E •
Rapid
changes in translocation patterns in soybeans following
source-sink alterations. Plant Physiology 64: 652-655.
FERGUSON, I.B.; CLARKSON, D.T.
1976.
Simultaneous uptake
and
translocation
of
magnesium
and
calcium
in
barley(~r~~u~ ~J~are L.) roots.
Planta 128: 267-269.
FITTER, A.H.;
HAY, R.K.M.
1981.
Mineral
nutrients,
p.68-117.
In:
~~l!onmental
physiology of plants.
London: Academic Press.
GARWOOD, E.A. 1968. Some effects of soil-water conditions
and soil temperature on the roots of grasses and clover.
2. Effects of variation in the soil-water content and in
soil temperature on root growth. Journal of the British
§.E. a ~_sJ_~_!!s!.. i2~~!y 23: 11 7- 128 •
Ibb
GERSANI, M., LIPS, S.H.; SACHS, T.
shoots, roots, and hormones
The influence of
sucrose distribution.
1980.
on
i.~u.c!')al of ~xp~!:t!~~__I].!:_~l ~ot~.QL 31:
177-184.
GOUBRAN, F.H.; RICHARDS, D. 1979. The estimation of root
length in samples and sub-samples.
Comparision of a
visual and an automatic method.
Plant and Soil 52:
77-83.
GRAHAM, J.;
u pt a k e
SANDERSON, J.
1974.
Water
CLARKSON, D.T.;
by the roots of marrow and barley plants.
~.9f_i~~J-.!.!:I_ral. Re_search Coun~_i.l. Letcombe Laboratory
Annual
R~P9 r 1.
1Jl.ll
p. 9 - 1 2 •
GRAHAM, R.O.; BOWLING, D.J.F. 1977. Effect of the shoot on
the transmembrane potentials of root cortical cells of
sun flo we r • .:!. 0 u ~J:!~ 0 f Ex per i men tal Bot any ~ : 886 - 89 3 •
GRAVES,
C.J.
1983.
The
nutrient
film
technigue.
Hortcicultural
Reviews 5 : in press.
-_ _ - - - - - - -----HACKETT, C. 1968. A study of the root system of bar 1 ey.
I.
Effects
of
nutrition
on two varieties.
The New
287-299.
f.~Y~~9jLL?-.!. §2:
HACKETT, C. 1972. A method of applying nutrients locally to
roots under controlled conditions, and some morphological
effects of locally applied nitrate on the branching of
wheat roots.
Australian Journal of Biological Sciences
..
25:
...
1169-1180.
HAHN,
S.K.
1977.
A quantitative
approach
to
source
potentials and sink capacities among reciprocal grafts of
sweet potato varieties. ~ Science 1I: 559-562 •
. HALLMARK, W.B.;
BARBER, S.A.
1981.
Root
growth
and
morphology, nutrient uptake, and nutrient status of
soybeans as affected by soil K and bulk
density.
Ag_ro~l ~ur.!!..~
71.:
779-782.
HARRADINE, A.R.; WHALLEY, R.O.B. 1981. A comparasion of the
root
growth, root morphology and root response to
defoliation of ------Aristida -----ramosa R.Br.
and Danthonia
linkii
Kunth.
Australian
Journal of ~~ltur!l
R~s ~~!c!!
g:
567 - 57 4 •
HATRICK, A.A.;
BOWLING, D.J.F.
1973.
A study
relationship between root and shoot metabolism.
2.f.
EXP'~!:jJ!!~_n!.~l ~o~~ 24:
607-613.
of the
Journal
to/
HEGARTY, ToW. 1973. Seedl ing growth in controlled-nutrient
con d i t ion s • ~Q.~..r Q. ~_l .91. ~~p..~~_i...m e !.!!_il ~.-2..~ 24 : 130 - 13 7 •
HEROLD, A.
1980.
Regulation of photosynthesis by sink
act i v i t Y - the miss i n g 1 ink.
The Ne wt.~y_t 0 1 0 g i s t 8 6 :
131-144.
\._ HODGKINSON, K.C.;
BAAS BECKING, H.G.
1978.
Effect of
defoliation on root growth of some arid zone perennial
p 1ant s • ~~ str~J.L<!.!l ~_Q_~!,B..cD. 0 fAg ric u 1 t u r a 1 Res ear c h 2 9 :
31-42.
HOPKINSON, J.M. 1964. Studies on the expansion of the leaf
surface.
IV.
The carbon and phosphorus economy of a
1 ea f • ~Q~ _'C!.!~l Qi. Expe r_i...me_!!!il Bot a ny 1i.:
125 -13 7.
HORGAN, J.M.; WAREING, P.F. 1980. Cytokinins and the growth
responses of seedlings of Betula pendula Roth. and Acer
~~~dQ£li!ftnus h.
to nitrogen and phosphorus deficiency.
~~u~~~l Qi. ~~£erimental Botany ll:
525-532.
HUMPHRIES, E.C.; THORNE, G.N.
1964.
The effect of root
formation on photosynthesis of detached leaves. Annals
Qi Bot~!.!y ~.~.28: 391-400.
HUNT, R. 1973.
A method of estimating root efficiency.
~Q u_'C.~~ 0 f ~£ll e dEc 01 09Y lQ.:
1 57- 164 •
HUNT, R. 1975. Further observations on root-shoot equilibria
in perennial ryegrassChQlium perenne L.).
Annals of
~t~nl li:
745-755.
HUNT, R. 1976. Significant relationships in the analysis of
root-shoot equilibria. Annals Qf Bota!!y 40: 895-897.
-HUNT, R. 1977. Significant relationships in the analysis of
root-shoot equilibria: a further explanation. Annals of
~~~~nl!l:
657-659.
The institute of
HUNT, R. 1978. f~nt .9J:.9_wth analysis.
96.
London:
biology
studies
in
b i 010 gy
No.
Edward-Arnold.
HUNT, R. 1979. Plant growth analysis: the rationale behind
the use of the fitted mathematical function. Annals of
Bo~~!.!y 43:
245-249.
HUNT, R. 1981. The fitted curve in plant growth studies,
p.283-298.
In:
Rose, D.A.;
Charles-Edwards, D.A.
~~!~~~~~~~
and ~~!!! ~ysiol~.
London:
Academic
Pre s s.
.'
16U
HUNT, R.
1982.
E~n!.9..rQwt-.t!. ~u__ !:~~.
~Q ~~~!. 5!r~~!l!. ~naly_~i?..
lh~ fJL~~:LiQ!1_'!.l ~J~P~Q~_s:Jl
London: Edward Arnold. 248p.
HUNT, R.;
BURNETT, J.A.
1973.
The effects of
light
intensity and external potassium level on root/shoot
ratio and rates of potassium uptake
in
perennial
ryegrass(.!:.Qlium
~enne
L.).
Annals of Botany 37:
519-537.
HUNT, R.; STRIBLEY, D.P.;
READ, D.J.
1975.
Root/shoot
equilibria
in Cranberry(Vacc~ium macrocarpon Ait.).
807-810.
~~n~l~ Qi Botany 39:
JESCHKE, W.O. 1982. Shoot-dependent regulation of sodium and
potassium fluxes in roots of whole barley seedlings.
601-618.
~Qu~~~l of Experjm~ntal Botany ll:
KEMPF, J.S.; PICKETT, S.T. 1981. The role of branch length
and angle in branching pattern of forest shrubs along a
successional gradient. The ~~~ Phytologist 88: 111-116.
LAMBERS, H.;
POSTHUMUS, F.
1980.
The effect of light
intensity and relative humidity on growth rate and root
respiration of Pla~~ lanceolata and Ze~~. Journal
Qf. ExR~~i!!}~J:!l~ ~~1~ ~: 162 1- 1630 •
LEDIG, F.T.; PERRY, T.O. 1965.
Physiological genetics of
the shoot-root ratio.
Society of American Foresters
~~etin~ 1960 Pr~ce~dings p.39-43.
LEE, R.B. 1982. Selectivity and kinetics of ion uptake by
barley plants following nutrient deficiency. Annals of
Bot~nl~:
429-449.
LEONARD, R.T.; HANSON, J.B. 1972. Induction and development
of increased ion absorption in corn root tissue. Plant
EhY~lo.lQ~l 49:
430-435.
LONERAGAN, J.F.; SNOWBALL, K. 1969a.
Calcium requirements
of plants.
Au~~rall~ Jou~nal of Agricultural Research
20: 465-478.
LONERAGAN, J.F.;
SNOWBALL, K.
1969b.
Rate of caliucm
absorption by plant roots and its relation to growth.
~s~r~}la.!:!. ~u~l'!~l of Agricultural Research 20:
479-490.
LONERAGAN, J.F.;
SNOWBALL, K.;
SIMMONS,
W.J.
1968.
Response of plants to calcium concentration in solution
c u 1t u r e • ~~~~i!l ian J 0 ~~~ 0 fAg ric u 1t u r a 1 Res ear c h 19 :
845-857.
lb~
LOVETT DOUST, L.
1981.
Population dynamics and
local
specialization in a clonal perennial (R~f!uncu.lus r?~.I!.~J.
1. The dynamics of ramets in contrasting habitats.
~Q~ !':.t1.ii.1 0 f
L~ 0 12.91. ~:
LUCKWILL, L.C. 1960. The physiological relationships of root
and shoot. Scientific
- ------- Horticulture 14: 22-26.
LUTTGE, U.; HIGINBOTHAM, N. 1979. Transport regulation in
the plant as a whole, p.352-369.
In: Transport in
£.J_~.1!!2.
Springer-Verlag: New York.
MCDAVID, C.R.; SAGAR, G.R.; MARSHALL, C. 1973. The effect
of
root
pruning l~nd
6-Benzylaminopurine
on the
chlorophyll content,
CO fixation and the shoot/root
2
ratio
in
seedlings of Pisum sativum L.
The New
Phy~ologi~~ 72:
465-470.
MCLACHLAN, K.D.; DE MARCO, D.G.
1982.
Acid phosphatase
activity of intact roots and phosphorus nutrition in
plants. III. Its relation to phosphorus garnering by
wheat and a comparision with leaf activity as a measure
of phosphorus status. Australian Journal of Agricultural
Research
33: 1-11.
-.. -- --NEWMAN, E.I. 1966. A method of estimating the total length
of root in a sample.
Journal of ~p.lied Ecology~:
139-145.
NELSON, L.E. 1967. Effect of root temperature variation on
growth and transpiration of cotton(Gossypium birsutum L.)
seedlings. Agronomy Journal~: 391-395.
NIELSEN, K.F. 1974. Roots and root temperature, p.293-333.
In:
Carson, E.W.
The plant root and its environment.
Charlottesville: University Press of Virginia.
NIELSEN, K.F.;
HUMPHRIES, E.C.
1966.
Effects of root
temperature on plant growth. Soils and Fertilizers 29:
1-7.
NYE, P.H.; TINKER, P.B. 1969. The concept of a root demand
coefficient. Journal Qf Applied Ecology~: 293-300.
..
J
74 3- 7 5 5 •
170
OSMOND, D.L.; RAPER, C.D.,JR.
1981.
Growth and nitrogen
accumulation in tobacco plants as affected by nitrate
concentration, root temperature and aerial temperature.
~9_ r _~~ 2 !~Y. ~ u_!:!!~l Zl:
49 1 - 49 6 •
OSWALT, D.L.; BERTRAND, A.R.; TEEL, M.R.
1959.
Influence
of nitrogen fertilization and clipping on grass roots.
~~l Sci~_~~~ ~<;:i~y..Qi. Am_~rica Proceedings~:
228-230.
PANDEY, B.N.; SINHA, R.P. 1977. Light as a factor in growth
and morphogenesis.
1.
Effect of artificial shading on
sericea Retz.
The New
fE. o!?:}_ ~!:L~. j ulJ~~~ L. and C.
E.hy ~_ ol~_gi~1. l!i: 4 31 - 4 39 •
PE ET , M.M.;
KRAMER, P.J.
1980.
Effects of decreasing
source/sink
ratio
in
soybeans
on photosynthesis,
photorespiration, tranpiration and yield. Plant and Cell
Environment 3: 201-206.
PERRY, T.O.
1971.
Winter
season
photosynthesis
and
respiration by twigs and seedlings of deciduous and
evergreen trees. Forest Science 17: 41-43.
PHILLIPS, I.D.J. 1964.
Root-shoot hormone relations.
I.
The
importance
of an aerated root system in the
regulation of growth hormone levels in the shoot of
!:L~ 1~.!!!h.L!~ ~!!~~.
Ann a 1s 0 f Bot a ny, !i. i. 28 : 1 7 - 35 •
PHILIPSON, J.J.;
COUTTS, M.P.
1977.
The influence of
mineral nutrition on the root development of trees. II.
The effect of specific nutrient elements on the growth of
individual
roots
of
sitka
spruce.
Journal
of
IXp'~!j_.m._~~t al Bot ~.!!i:. ~:
1071-1075.
Effect of subsoil
PINKERTON, A.;
SIMPSON, J.R.
1981.
acidity on the shoot and root growth of some tropical and
temperate forage
legumes.
~~tralian
Journal
of
~~ric_u_l!~r.~ ~~~ea!~l!. g:
453-463.
PITMAN, M.G. 1972. Uptake and transport of ions in barley
seedlings.
III.
Correlation between transport to the
shoot and relative growth rate.
Australian Journal of
~i2l-"~..~Li cal Sci en c e s ~:
905 - 919.
PORTER, J.R. 1983a. A modular approach to analysis of plant
growth.
I. Theory and principles. The New Phytologist
94: 183-190.
PORTER, J.R. 1983b. A modular approach to analysis of plant
growth.
II.
Methods and results. l~ ~e\'I PJltl..0lo~i~
94: 191-200.
1974.
POWELL, C.LI.
Effect of P fertilizer
on
root
morphology and P uptake of Carex coriacea. Plant and
Soil 41: 661-667.
POWER, J.F.; GRUNES, D.L.;
WILLIS, W.O.
REICHMAN, G• A. ;
1970.
Effect of soil temperature on rate of barley
development and
Journal
62:
nutrition.
Agrono~
--567-571PROCHAZKA, S. 1981. Translocation of growth regulators from
roots in relation to the stem apical dominance in
Pea(Pi_s.l:L~ ~~!_!..-'{um
L.)
seedlings,
p.407-409.
IN:
Brouwer, R.
et al.
~~,:!ctu~
and functi~~ of plant
root s.
The Hague:
Nijhoff/Dr
W.
t~artinus
Junk
Publishers.
RAPER, C.D.,JR.; OSMOND, D.L.; WANN, M.; WEEKS, W.W. 1978.
Interdependence
of
root
and
shoot activities in
determining nitrogen uptake rate of roots.
Botanical
Gazette
139:
289-294.
----REYNOLDS, J.F.;
THORNLEY, J.H.M.
1982.
A
shoot:root
partitioning model. Annals Qf Botany 49: 585-597.
RICHARDS, D. 1977. Root-shoot interactions:
a functional
equilibrium for water uptake in peach[Prunus persica (L.)
BatschJ. Annab. Qf Botany !l: 279-281RICHARDS, D.
1978.
Root-shoot interactions:
functional
equilibria for nutrient uptake in peach(Prunus persica L.
Batsch). Ann~ of Botany 42: 1039-1043.
RICHARDS. D.
1981.
Root-shoot interactions in fruiting
tomato plants, p.373-380. In: Brouwer et al. Structure
The Hague:
Martinus
~~ !u ~~~_ i o~ of Qla n1 roots.
Nijhoff/Dr W. Junk Publishers.
RICHARDS, D.; GOUBRAN, F.H.;
GARWOLI, W.N.;
DALY, M.W.
1979a. A machine for determining root length. Plant and
Soil -52: 69-76.
---RICHARDS, D.;
GOUBRAN,
F.H.;
COLLINS,
K.E.
1979b.
Root-shoot equilibria in fruiting tomato plants. Annals
Q.f. Bo!.~~ 43: 401-404.
J. I l..
for
RICHARDS, F.J.
1959.
A flexible growth
function
empirical
use.
Journal of
290-300.
RICHARDS, D.;
R. N•
1977a.
Effects
of
ROWE,
root
restriction, root pruning and 6-Benzylaminopurine on the
growth of peach seedlings.
Annals of
Botany
41:
729-740.
RICHARDS, D.; ROWE, R.N. 1977b. Root-shoot interactions in
peach:
the function of the root. Annals of Bo~ 41:
1211-1216.
RICHMOND, A.E.; LANG, A. 1957. Effect of kinetin on protein
content
and
survival of detached Xanthium leaves.
Science 125: 650-651.
ROMHELD, V.; MARSCHNER, H.
1981a.
Rhythmic iron stress
reactions
in
sunflower at suboptimal iron supply.
f.hY~lolo_.s~ Ql~nta!um.?J.:
347-353.
ROMHELD, V.; MARSCHNER, H. 1981b.
Iron deficiency stress
induced morphological and physiological changes in root
tips of sunflower. ~iolo~ Plan~rum.?J.: 354-360.
RUFTY, T.W.; RAPER, C.D.,JR.; JACKSON, W.A. 1981. Nitrogen
assimilation, root growth and whole plant responses of
soybean to root temperature, and to carbon dioxide and
light in the aerial environment. The New Phytologist 88:
607-619.
RUSSELL, R.S. 1977. Plant ~oot systems. Their function and
interaction with the soil. London: tkGraw-Hill.298p.
SACHAN, R.S.; SHARMA, R.B. 1981. Calcium absorption as an
index of root parameters of cucumber(Cucumis sativus L.).
Plant and Soil 59: 129-133.
SKENE, K.G.M. 1975.
Cytokinin production by roots as a
factor in the control of plant growth, p.365-396. In:
The development
and
Torrey, J.G.;
Clarkson, D.T.
function of roots. London: Academic Press.
SZANIAWSKI, R.K.; KIELKIEWICZ, M.
1982.
Maintenance and
growth respiration in shoots and roots of sunflower
plants grown at different root temperatures. Physiologia
Plantarum 54: 500-504.
THORNE, G.N. 1959. Photosynthesis of lamina and sheath of
barley leaves. ~.!l..n~.l2. of ~Qt_~, N.S. 23: 365-370.
,
Influence of assimilate
THORNE, J.H.; KOLLER, H.R. 1974.
demand
on
photosynthesis,
diffusive
resistances,
translocation, and carbohydrate levels of soybean leaves.
f..Jan!. EJ!ysLQJQg,l~: 201-207.
THORNLEY, J.H.M. 1972. A balanced quantitative model for
root:shoot ratios in vegetative plants. Annals Qf Botany
36: 431-441THORNLEY, J.H.M. 1975. Comment on a recent paper by Hunt on
shoot:root ratios. Anna~ of Bo~ 39: 1149-1150.
THORNLEY, J.H.M.
1976.
Mathematical
models
in
plant
E..b.y s.~.o 1_!?~.l.· A qua !!.~l!.~_~ i ve ~oac h to p rob 1ems ~ p 1 ant
~~ £!:.~£. ..e.bX.?_.:L<?J~.9.Y.
London: Academic Press. 318p.
THORNLEY, J.H.M.
1977.
Interpretation
of
shoot:root
relationships. ~~als of BotanY!l: 461-464.
THORNLEY, J.H.M.
1980.
Research strategy in the plant
sciences. Plant
and
Cell
-- - - - Environment 3: 233-236.
TOLLENAAR, M.; DAYNARD, T.B. 1982.
Effect of source-sink
ratio on dry matter accumulation and leaf senesence of
maize. Canadian Journal of Plant Science 62: 855-860.
TROUGHT, M.C.T.; DREW, M.C. 1981. Alleviation of injury to
young wheat plants in anaerobic solution cultures in
relation to the supply of nitrate and other inorganic
nut r i e nt s • J 0 u l" y!~ 0 f ~~ i men tal Botany ~: 509-522.
TROUGHTON, A. 1960.
Further studies on the relationship
between shoot and root systems of grasses. Journal of
the !Lr:'il1~!:!. §"!:~~_~l<!!.!£ So~ili li: 41- 47.
TROUGHTON, A. 1977. The rate of growth and partitioning of
assimilates in young grass plants: a mathematical model.
~_~n~1 .Qf ~~anY!l:
553-565.
TROUGHTON, A. 1981. Root-shoot relationships in mature grass
plants. f~~!. ~~ iQil £2: 101-105.
VAADIA, Y.; ITAI,C. 1969. Interrelationships of growth with
reference to the distribution of growth substances,
p.65-79. In: Whittington, W.J. Root growth.
London:
But t e rw 0 r t h s •
VEEN, B.W. 1977. The uptake of potassium, nitrate, wat e r,
and oxy ge n by a maize root system i n re 1 at ion to its
s i z e. ~':J.rl!_a.l .Qf ~rim_~ntal Bot~ 28: 1389-1398.
VEEN, B.W. 1982. The influence of mechanical impedance on
the growth of maize roots. Plant and Soil 66: 101-109.
VEEN, B.W.; BOONE, F.R. 1981. The influence of mechanical
resistance
and
phosphate supply on morphology and
function of corn roots. Plant
and
Soil
-- - - - 63: 77-81.
VENUS, J.C.; CAUSTON, D.R.
1979.
Plant growth analysis:
the use of the Richards function as an alternative to
pol y no In i ale xpo ne nt i a 1 s • ~!'!.!! a 1s Q.f. Bot a n,y 11: 623 - 632 •
WALKER, A.J.; HO, L.C. 1977. Carbon translocation in the
Effects
temperature on carbon
tomato:
of
fruit
metabolism and the rate of translocation.
Annals of
~ot.~nl.i!.:
825-832.
WARDLAW, I.F.; MONCUR, L. 1976. Source, sink and hormonal
control of translocation in wheat. Planta 128: 93-100.
WAREING, P.F.; PATRICK, J. 1975. Source-sink relations and
the partition of assimilates in the plant, p.481-499.
~:
Cooper, J.P.
Photos,ynthesis and productivit,y in
Cambridge University
different environments.
London:
Pres s.
WARREN-WILSON, J. 1972. Control of crop processes p.8-30.
In:
Rees, A.R.
et al. ~ processes in controlled
environments.
London: Academic Press.
----_._-----WENT, F.W. 1943. Effect of the root system on tomato stem
growth. flant ~ysiology~: 51-65.
WILD, A.; BREEZE, V.G. 1981. Nutrient uptake in relation to
growth.
p.331-344.
In:
Johnson, C.B. Physiological
£roce~~~
llmi~~
plant
QiQductivit,y.
London:
Butterworths.
WINSOR, G.W. 1978. Nutrient-film culture: an appraisal of
its progress and prospects for crop production under
g 1ass • hl~ ?_~ 0 u ~ CrQ'p'~ Res ear chI n s t it ute Ann u a 1 Rep 0 r t
1977. p.185-195.
WINSOR, G.W.;
1978.
Some aspects of the
t~ASSEY,
D.M.
nutrition of tomatoes grown in recirculating solution.
Acta- -Horticulturae
82: 121-132.
--------_.---- WOODHOUSE, P.J.; WILD, A.; CLEMENT, C.R.
1978.
Rate of
uptake of potassium by three crop species in relation to
growth. ·~~u.r:~-.l of EX2erimental Botany~: 885-894.
30
28
26
24
C')
22
...
~ 20
0
~
C\I
:<:
,U
j
18
~
16
a:
w 14
a::::
a:
LL 12
a:
w
--1 10
+
+
../"
i
~i
11
-i
--l
~l
8
~
6
4
2
0
0
25
30
35
40
45
50
55
2
'ROOT LENGTHlx10 Ml
Appendix l~ The effect of different levels of ionic strengths and light
lntensities on the relationship between root length and leaf
area. +;full strength *;5% strength.
Slope and confidence
1iWI"t fOr full strength and 5% strength treatments are;
4.0 3±O. 29, 1.669±O.0902 (Light intensity treatments were
excluded from the symbols)
5
10
15
20
60
>--'
......,
(J";
400
+
350
+
300
250
n::
/
t00~
LL
~
+
a:
w
-I
150
100
*
50
0;-
2
1
6
8
10
12
11
16
18
20
22
21
26
28
ROOT NUMBERlx10 4 /
Appendix 2. The effect of different levels of ionic strengths and light
intensities 00 the relationship between foot number anQdleaf
number. +;ful I strength ;0% strength. S ope and confl ence
limit
for
full. strength A
an·a 5% strength treatments
are;O.00128±O.00032, O.00075±u.00021
30
I-'
'-J
O'l
177
Appendix 3:
Plants grown in low solution
temperature with (left) and without
(right) aerial roots on the stem
below the cotyledons. Note the
differences in leaf colour.
.90
r
.85
.80
e
G .75
'-
C)
'-'
b..
.70
,....
b..
e
CS)
, .65
.-.
*
'-'
8 .60
I-
<J:
~
l-
.55
e
e
~ .50
'I-
*
8 .45
~
.40
+
+
.35
.30.
9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1/ACTIVITY RATIO WITH RESPECT TO K (G/G/OAY)/(G/G/OAY)
Appendix 4. The effect of root restriction and presence of aerial root
on tne relationshlp' between the mass ratio and the reciprocal
of activity ratio with respect to potassium uptake.
+;weight of aerial root in shoot w~ight
e;weiqht of aerial root in root welgnt
*;restrlcted root in small container
~;unrestricted root
1.7
I-'
-....j
CD
1.5
..j
1.0
3.5
C)
3.0
IZ
W
I-
z 2.5
u
0
L:
::J
t-i
u
2.0
---1
IT
U
---1
IT
+
1. 5
le)
I-
1.0
.5
0
0
5
10
15
20
(M)X10 2
25
30
-ROOT LENGTH
Appendix 5L The effect of different levels of nitrogen and calcium on
~he
relatlonship between root length and total calcium
content • • ~full nutrition +;lQw-cal~ium *;low-nitrogen. Slope
and confiaence limit for ful I nutrltion, and low-calcium plus
low-nItrogen treatments are;
O.UOIY9±O.00055, O.000661±O.000213.
35
....'-J
\.D
lao
! !.
.·illll. nO!.
50. XSl) X61. 19X2
:'\'
Appendix 6
Relationship between Shoot and Roots of
Cucumber Plants under Nutritional Stress
G. C. CHUNG, R. N. ROWE and R. J. FIELD
Departlllents of f/orticlIltllrl' und Plant Science. Lincoln College, Call1erhllry, New Zealand
Accepted: I lune 1982
Key words: ClIclImis sativlIs L., cucumber. root. shoot morphology. nutrition.
Richards and Rowe (1977 a, b) showed that a relationship exists between the morphological
characteristics of plant roots and shoots and suggested that they should be taken into
account when considering the functional relationships of roots and shoots as they relate
to total plant growth. They showed that under the particular nutritional conditions of
their experiment root length and leaf area were related and linked in some way through
their common involvement in water and nutrient uptake. Root number and leaf number
were also related through their common involvement in differentiation processes.
Thornley (1977) in discussing the empirically derived functional equilibrium equation
proposed by Hunt (1975) suggested the equation:
f
m = !J..Af
!J..W
(I)
as a simpler and more correct form of the relationship between plant mass and nutrient
uptake provided certain assumptions were made. !J.. Wand !J..M are the increments of total
plant dry weight and total weight of an element(s) taken up respectively in unit time.
The experiment described in this present paper was designed to establish empirically
whether the inclusion of morphological parameters of root and shoot growth in the
equation proposed by Thornley could satisfactorily describe the performance of plants
over time with their roots growing in a wide range of nutrient solution concentrations,
depths and volumes.
Cucumber (C'llClll11is sativlIs L.) seedlings were grown in a continuous circulating flow
system for 9 weeks in full strength, 5 or 2 per cent dilutions of Cooper's solution (Cooper,
1975). Solution depths and volumes respectively of I mm (19·6 em:!), 5 cm (980 cm:!) and
5 cm (19·6 cm:!) were controlled by container size and adjustable stainless steel mesh trays.
Solutions were changed regularly to maintain nutrient concentrations as near to
treatment specifications as possible and water losses were replaced by an automatic
metering system. Plants were harvested three times throughout the experiment at regular
intervals of 3 weeks. Plant dry weight. root number and length and leaf number and
area were measured and tissue analysed for calcium and potassium content. All female
flowers were removed as they appeared.
Plotting all the data in the manner suggested by Thornley [Eqn (I), Fig. I (al].
OJ05-7.lo4:X2' 120HS9 + OJ $03.00;0
(. 19X2 Annals or Botany Company
181
Chllllg ct al--- Relatiollships h£'tll'('('1/ shoot and root ill CliclIIllher
480~--------------------~
6
( b)
-'-
E
0c
:u0.
CO'
,
4
0
~
0
0
o
~
o
0c
f-
'0OJ
'3
0
0
f-
o
lO
20
30
40
15
0
Total Co+K( g)
45
30
60
Total CO+K per root no.
root length-' (g per no. em-')
480
6
( e)
(d)
5
"0 4
:u
.c
E
NE
c
~
'0OJ
0
::>
3
~
-
...J
0
0
OJ
2
...J
0
300
450
Root number (x 10 3)
600
0
r
Low streng th
2'5
5'0
Root length (m
7·5
10'0
x103)
FIG. l. The functional equilibrium relationships obtained from (a) Eqn (I), (b) Eqn (2) and its components (c), (d). Each value is the mean of four replicates and there are 27 values for each figure. To
improve clarity only non-overlapping mean values are plotted. (a) Full strength y = 12·71x+3·34,
r = 99-4; low strength y = 28-46 x-l·78, r = 90·7. (b) y = 0·092x-0·026, r = 97·5. (c) y = 0'70
x+ 15·5, r = 96·0. (d) Full strength y = 5·27 x+340'8, r = 98·4; low strength y ~ 1·98 x+382-4,
r = 95-4.
indicates that the data are best described by two regression lines (the initial values of
Wand M have been put equal to zero). In the diluted solutions, the slope of the line
is greater than in full strength solution, showing that the Jill in Eqn (I) is not constant
over the range of nutrient dilutions used in this experiment. The plot of leaf number
against root number produced a single regression line [Fig. I(c)]. Leafarea plotted against
root length produced two regression lines [Fig. I (d)] with the slope for the dilute solutions
being less than that for the full strength.
Over the range of plant size where comparisons can be made, it appears that the
cucumber adapts to nutritional stress by increasing root length relative to its leaf area
and decreases its calcium and potassium uptake relative to its total dry weight. Total
182
Chllllg et ai-Relationships he/II'C('II Shoo/
(Jilt!
Roof ill CliclI/nher
root length increases by increasing the lengths of individual roots with no increase in
root number.
The leaf area/root length relationship is consistent with the observation that in the
dilute solutions the plants allocated a greater proportion of their overall total dry weight
to the root than in full strength solution, even though total plant weight was smaller.
It could be speculated that dry weight allocation was directed to maintaining root length
at the expense of individual leaf area expansion,
When the data were plotted according to the emperically derived equation:
total dry weight of plant total weight of element' M'
leaf number x leaf area-- l oc root number x root length 1
(2)
a single linear regression line describes the relationship [Fig. I (b)] and indicates that such
an Eqn, at least with cucumber over a wide range of nutrient concentrations, gives a
better description of plant growth than the Thornley or Hunt equations alone, The
different solution depths and volumes within one nutritional treatment did not alter the
regression line despite the fact that in some treatments a significant proportion of the
total root system was exposed to the air.
Further work is in progress to establish whether this equation describes plant growth
adequately under-other forms of stress.
LITERATURE CITED
COOPER, A. 1.. 1975. Crop production in recirculating nutrient solution. Sci. Hort. 3, 251-8.
HUNT, R., 1975. Further observations on root-shoot equilibria in perennial ryegrass (Lotium perenne L) Ann.
Bot. 39, 745-55.
RICHARDS, D, and ROWE, R. N., 1977 a. Effects of root restriction, root pruning and 6-Benzylaminopurine on
the growth of peach seedlings Ibid 41, 728-40.
- - - - 1977 b. Root-shoot interactions in peach; the function of the root. Ibid 41, 1211-6,
THORNLEY, ], H. M., 1977. Interpretation of shoot-root relationships. Ibid 41, 461-4.