Copyright is owned by the Author of the thesis. Permission is given for
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THE INFLUENCE OF PHOSPHORUS S UPPLY
ON BELOW GROUND INTERFERENCES
BETWEEN BROWNTOP AND WHITE CLOVER
A Thesis presented i n partial fu lfilment of
the requirements for the degree of
Doctor of Philosophy in Soil Science
at Massey University
CLAIRE ASTLEY PANNELL
1993
i
ABSTRACT
A low occurrence of white clover in pastures contributes to soil nitrogen
(N)
deficiency
and a low quality feed for stock. There is evidence to suggest that competition for soil
phosphorus (P) from roots of browntop plays an important role in determining the
distribution of white clover in hill country swards. However, competition for soil P
between roots of browntop and white clover has not been studied separately from other
factors known to affect the growth and persistence of white clover (e.g., soil moisture,
grazing management, shoot interferences (shading and physical impedance), and non­
competitive root interferences).
In hill country pastures, P level (phosphorus fertilisers), and defoliation (grazing
management), are the main factors that can be changed by farmers to alter pasture
botanical composition. The high cost of superphosphate has limited the potential of
farmers to manipulate pastures using fertiliser applications. Therefore, it is important to
know whether roots of browntop compete with roots of white clover for soil P, and
whether a low supply of soil P will contribute to more severe competition from browntop
roots. The possibility of non-competitive interferences occurring between roots of
browntop and white clover must also be considered. How defoliation alters the balance
of P acquisition between roots of brown top and white clover needs to be determined.
Three techniques were employed to examine the nature of root interferences occurring
between browntop and white clover: plant strategies; dual P isotope labelling; and a
�
mor . traditional competitive settings trial using aerial partitions. Plant growth and root
I
interferences were studied at a range of levels of soil P supply. Responses of growth
and phosphorus uptake of browntop and white clover to increasing soil P supply were
examined first, in the glasshouse, by growing monocultures of browntop and white
clover in pots.
Two mini-sward trials (one at deficient soil P supply, the other at adequate to luxury soil
P supply) were carried out in the glasshouse to allow examination of root interactions
(without shoot interactions). The basis of the experimental design was to determine the
relative amounts of phosphorus-32 and -33 absorbed by a central row of plants (either
browntop or white clover) from two adjacent soil spaces, one dominated by white clover
roots, the other by browntop roots. 32p was injected into the soil on one side of the
central row of plant , and 33p into the other side. 32p and 33 p uptake was assessed
;
by harvesting the shoots of the central plants, and counting the two isotopes.
ii
The competitive settings type trial compared the growth and P uptake of a single central
plant in a small pot (no interference with other plants) with a central plant in a larger pot
grown with roots associated with roots of plants of the same species (intraspecific
association), or of the other speCies (interspecific association). Shoots of the central
plant was separated from the shoots of outer plants by an aerial partition.
The growth of browntop and white clover, and the nature of root interferences occurring
within and between the two species was dependent on the level of soil P supply.
However, the higher root density and specific root length (SRL) of browntop compared
with white clover appeared to be the most important factor determining the success of
browntop at all levels of soil P supply, regardless of whether or not browntop was
grown with white clover.
According to the plant strategy theory of Grime, browntop was found to be a stress
tolerant plant. At low levels of P �upply, the lower growth rate of browntop compared
with white clover would be an important factor contributing to the dominance of browntop
in hill country pastures. At adequate to luxury levels of soil P supply, shoot growth of
browntop was more responsive than white clover, and browntop was capable of
luxury consumption of P. The high growth rate and large demand for P contributed to the
competitiveness of browntop at high P supply. However, the lower demand for P by
white clover, and the high P supply may have enabled white clover to avoid
competition with browntop.
\
i
On unamended subsoil, browntop reduced P acquisition by white clover roots, and had
a greater P uptake in the presence of roots of white clover than with roots of other
browntop plants. Therefore, evidence of root competition for soil P from browntop with
white clover was found. The competitive effect of brown top appeared to be due to
browntop decreasing the availability of P in the soil, explained by browntop's ability to
acquire more radioactive P from the soil than white clover.
At low P supply (subsoil), P application, but not defoliation of browntop, reduced the
!
competitiveness of brown op. At adequate P supply, the ability of browntop to acguire
P was reduced by defoliation. The effect of defoliation was rapid (four days), and
browntop was able to acquire P isotope to higher concentrations in the shoots than
when undefoliated. Possibly the reduction of root competitiveness of browntop may be
short-lived.
iii
Some interference, other than root competition, was occurring at intermediate to luxury
levels of soil P supply, and may have masked the competitive effects of browntop.
White clover appeared to benefit for P acquisition from growing with browntop, due to
greater local root density compared with when growing with other white clover plants.
Therefore, brown top and white clover appeared to gain mutual benefit for P acquisition
from the presence of roots of the other species, and the competitive effects of brown top
were not of overriding importance. The possibility of autotoxicity of white clover on its
own root growth was discussed in relation to rhizosphere acidity effects on the toxicity
of phenolics.
At adequate to luxury levels of soil P supply, neither undefoliated browntop nor
undefoliated white clover benefited from defoliation of adjacently growing white clover
plants. However, at lower P supply, defoliation of white clover led to an increased P
isotope acquisition by nearby browntop plants. Therefore, defoliation reduced the
demand for soil P by white clover. Roots of browntop were not as tolerant of defoliation
as white clover.
In the field, the mat forming behaviour of browntop, physically impeding the growth of
white clover and shading white clover stolons, would reduce the severity of competition
for soil P between roots of browntop and white clover. Overall, root competition for P
from browntop with white clover was found not to be as imp�rtant as previously
thought.
'
\
'
The use of several experimental techniques allowed a clearer picture of the interferences
that occur between browntop and white clover to be obtained. The nature of root
interference changed with increasing P supply. The respon_ses of browntop and white
clover to increasing P supply was found to be enlightening when the plant strategy
theory of Grime was used to compare browntop and white clover. However, lhe dual P
isotope technique found plant interferences that were not detected by the other methods
used (P response and competitive settings trial}, and allowed interferences that were
occurring simultaneously to be elucidated.
iv
A CKNOWLE DGEMENTS
I wish to thank the following people for their encouragement and helpfu l advice
d uring m y Ph. D. programme:
Forem ost thanks to my supervisors; Professor Robert White for his patience and
helpful knowledge, Dr. Peter Kemp for h is enthusiasm and s upport, and D r.
Russ Tillman for sharing h is knowledge in the use of radio-isotopes and
support during the writing up of my thesis.
To the technicians of the Soil Science and Plant Science (Ag ronomy)
Departments for their continual assistance and knowledge in the field,
g lasshouse, and laboratory, special thanks for putting a sm ile on my face. Also
thanks to my friends that helped with the setting up and harvesting of the
glasshouse trials.
Sincere gratitude to my friends and colleagues at Massey U niversity and in the
broader Palmerston North comm unity. Thanks to those involved in the local
m usic i ndustry, especially Dave White, for making my time in New Zealand both
enjoyable and fruitfu l.
Roger Thomas and Gerard Creamer assisted greatly by providing access to
laser p rinting for the final production of my thesis.
\
\
'
I acknowledge the financial assistance of the Charles and Annie Neumann
Fellowship in Agricu lture, C. Aim a Baker Trust Fund, and Massey Un iversity
Research Fund.
Fi nal ly, a special thought for my fam ily and friends. This thesis is dedicated to
m y beautiful mother, Judith Pannell.
V
TABLE OF CONTENTS
Page
ABSTRACT
....................................................................................................
ACKNOWLEDGEMENTS .
.
TABLE OF CONTENTS
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LIST OF FIGURES
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. xxvii
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LIST OF APPENDICES ....... . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . ...... . . .. . . . .... xxvii i
vi
C HAPTER ONE
RESEARCH OBJECTIVES AND REVIEW OF
LITERATURE
Page
1 .0 Introduction and research objectives....................................................
1
1 . 1 Hill country pastures in New Zealand................................................... 4
1 .1 . 1 Effects of management practices and environ ment
on the botanical compositio n of hill pastures ... . . . . . . . . . ... ......... ... ..... 6
1 .2 Biology of browntop and white clover . . . . . . .. . . . . . . . . . .. . . . .... ... . . . . . . . . . . . . . . . .. . . . .. 8
1 .2. 1 Biology of browntop. ..... ....................................... ........................... .... 8
1 .2.2 Biology of whtte clover........................................... .......... .................. 8
1 .2.3 Root properties of browntop and white clover..................... . . .. . . . . . .
9
1 .3 Factors affect i ng P uptake by plants when grown i n association
_
with other plants........................................................................................ 1 1
1 .3. 1 Soil properties.. .................................................................. ....... ..... .... ..
1 1
1.3.1.1 Phosohate adsowtion and buffer caoacitv of soil..........
11
1 .3. 1 .2 SoilpH...................... ............................................ .... ..............
12
1 .3. 1 .3 Soil moisture content... .... ................. ............. ......... :. ...........
13
1 .3.2 Plant properties...................... ..................................... ................. ......... 1 4
1 .3.2.1, Absowtion from solution.......... ......... ... . . .. ...... .... ... .. .. .. .... .:··· 1 5
1 .3.2.2 Phvsical exploration and rate of extension of roots........ 1 6
1 .3.2.3 Modification of the rhizosphere... .. .... .. .. . ... . .. .. . ..... .. . . . . . .. . . . . . 1 8
.
1 .3.2.3. 1 P_C?Iysaccharide secretions..................................
1 .3.2.3.2 Acid secretion.......................................................
18
18
vii
Page
1 .3.2.3.3 Enzyme release.. ...... ..... ................ ........................
19
1 .3.2.3.4 Microbes in the rhizosphere. ....... .. . . . . . .. . .. . .. ... .. .. . . 20
1 .3.2.3.5 Mycorrhizae..... ......... ............. ........... . . . .. ...... ..... ...... 2 0
1 .3.2.4 Root cation exchange caoacitv and ner;ative
adSOIJ)tion.... ...... .. . .. . .. . .. . .... .. .. ..... . .. ... .. .. .. .. . .. . .. . .. . . .. .. .. . .. . . . . .. . . . .
1 .3.2.5 Metabolicactivitvofplants..................................................
21
22
1 . 3.3 Effects of defoliat io n on nutrient uptake by plants...... . .. . .......... .... 22
1 .3.3. 1 Root death and rate of elongation. .................................... 2 3
1 .3.3.2 Carbohvcirate supplv. .-. ..... ......... .................................... ....... 23
1 .3.4 I nd irect mechan isms affect ing P uptake by plant roots................. 2 4
1 .3.4. 1 Shading.................................................................................. 2 4
1 .3.4.2 Grazing management andpreference . ..................... ........ 25
1 .3.4.3 SUJ2Qivofother nutrients...................................................... 2 6
'
1 .3.5 Summarising comments................. ........................... ......................... 26
I
1 .4 Plant growth i nterference. ... .. .. .. . . . .. . ........... . .... . .. .... . . . .. .. ...... . .. ..... . ...... . ... . ... . 2 7
1 .4. 1 Negative interference........................................................................... 2 8
1 .4. 1 . 1 Competition............................................................................ 2 8
1 .4. 1 .2 Allelo.pathv.. ............................ . . . ...... . . . . . . . .... . . . . . . . . . . . . . . ... . . . . . . . . . .
28
1 .4.2 Positive interference.............................................................................. 30
1 .4.2 . 1 Phosohorus transfers between mvcorrhizal plants. . . . . ... 30
1 .4.2.2 Rhizos.phere effects.. ............................................................ 3 1
viii
Page
1 .4.2.3 Microorganisms in the rhizosohere......... .... . .... .......... ... .... 32
1 .4.2.4 Allelopathv. ........................ .............................. ......................
33
1 .5 Methods of studying plant interferences............................................. 34
1 .5.1 Monocuttu res.................. .... .................. ..................................... ... . .. .....
34
1 .5.2 Additive series................. .......................... ......... .................................. 36
1 .5.3 Replacement series...................................................... ..................... . . . 36
1 .5.4 Add i tion serieslbiva riate factorial design. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 37
1 .5.5 Dual labelli ng.................... ........................... ..... . ............. ...................... 3 8
1 .5.6 Divided pots........... .... �............ ......... .... .......... ................. ......... ............. 39
1 .5.6. 1 Aerial oartitions.....................................................................
39
1 .5.6.2 Below groundpartitions....................................................... 40
1 .6 Evidence of competition for P between roots of browntop an d
white c lover....................................................................................................... 4 1
1 .6. 1 Field surveys......................................................................................... 4 1
1 .6.2 Ability of roots to absorb P... ............... ..... .......... ................. .... . . . . . . . . . . . . 4 2
1 .6.3 Competttion experiments...................................................... .............. 42
1 .6.3. 1 Glasshouse trials.. ...... ... .. ...... . . ..... :···....................................
42
1 .6.3.2 Fieldtrials............................................................................... 44
1 .7 Conc lud ing comments.................................................................................
47
ix
CHA PTER TWO
RESPONSE OF THE GROWTH AND PHOSPHORUS
UPTAKE OF BROWNTOP AND WHITE CLOVER
TO INCREASING EXTERNAL PHOSPHORUS SUPPLY
Page
2. 1 Introduct ion......................................................................................................... 4 8
2.1 . 1 Objectives................................................................................................ 4 9
2.2 Materials and methods.................................................................................. 5o
2.2 . 1 The soil.................................................................................................... 50
2.2.2 Pla nting............... ..................................................................................... 50
2.2.3 Harvesting................... ......................... ................................................... 5 1
2.2.4 Mitscherlich response curves................................ .............................. 5 1
2.2.5 Statistical analyses and cu rve fitting procedures. . . . . . . . . . . . . . . . . .. . . . . . . . . . 52
2.3 Results................................................................................................................. 5 4
2.3. 1 Yield response curves.. ......... .. . ... .. .... . ....... ... .. . ... . .... .. ..... ... .. . . .. .. . .......... 5 4
2.3. 1 . 1 Shoot Yields............................................................................ 5 4
2.3. 1 .2 Tille r and rhizome yields of browntoo................................ 5 4
2.3. 1 .3 Root:shoot ratios.................................................................... 5 9
2.3.2 External P requirements for shoot growth ... . . . . . .. .. ...... . . . . . . . . . . . . . . . . . . . . . . . 5 9
2.3.3 P content of shoots and internal P requirements.. . . ......................... 6 0
2.3.3. 1 P concentration in shoots...... .. . . . . .... . .... . . ... . . . .. .. . . . . . . .......... . .. . 6 0
.
2.3.3.2 P contentofshoots................................................................. 6 0
2.3.3:3 P content of rhizomes and tillers of browntop........ . . . . .. . . . . . 6 3
2.3.4 P concentrat ion in roots... ... . .. . .. . ... ... . . ... ..... . . . . ..... .. .... .. . .... . ... . .. . . 6 3
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2.3.5 N concentration in shoots and roots ...
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2.4 Discussion ............
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2.4. 1 P stress tolerance...... ...
2.4.2 External P requirement................................................. ........................
2.4.3 Nutrient cycling
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2.4.4 Summarising comments .. .. . ..
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xi
C HAPTE R TH REE
THE EFFECTS OF SOIL PHOSPHORUS SUPPLY AND
DEFOLIATION ON THE INTER- AND INTRASPECIFIC
-
.
ROOT INTERFERENCES OCCURRING IN MINI-SWARDS
OF BROWNTOP AND WHITE CLOVER
Page
3.1
Introduction ......................................................................................................... 77
3.2
Materials and methods...... .... ...... ...... .... ... .. ..... ..... ........................... ........ .. .. 80
.
.
3.2.1 Experimental design and treatments................................................. 80
3.2.2 The soil.................................................................................................... 80
3.2.3 Watering.................................................................................................. 81
3.2.4 Planting.................................................................................................... 81
3.2.5 Aerial partitions...................................................................................... 81
3.2.6 Basal nutrients........................................................................................ 84
3.2.7 Injection of carrier-free radioactive phosphates ............................... 84
3.2.8 Harvesting............................................................................................... 85
3.2.9 Counting radioactive phosphorus-32 and -33................................. 89
3.2.1 0 Frequency distributions of no rmalised activities of
phosphorus-32 and -33. ..... ................................................................ 90
3.3
Results.................................................................................................................. 92
3.3.1 Effect of species association on phosphorus acquisition ...... ......... 92
3.3.2 Effects of defoliation on acquisition of radioactive
phosphorus-32 and -33..................... ............ ...................................... 95
3.3.2.1 Effects of defoliation of outer simulated sward soecies on
P isotope acquisition by central indicator browntoo and
white dover ............... ... ; ........................................................... 95
xii
Page
3.3.2.2 Outer simulatedbrowntop swards
.............................
3.3.3 Root properties
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3.3.3. 1 Effect of central indicator Sj)ecies on root prooerties of
plant species in the outer simulated swards
..
.
3.3.3.2 P depletion zone around roots
.......................
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95
......................
98
99
3.3.3.3 Root volume of central indicator plants and plants i n the
.
99
outer simulatedswards
.............................................. . .
.........
3.3.4 Shoot and root weights of central indicator plants. . .. . . . . . . . . . . .. . . . .. . . . . . 1 06
3.3.5 P and N content of shoots
.............................
3.4 Discussion
.
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3.4. 1 Evidence of root competition for soil P
.................................. . . . . . . . . . .
1 06
1 13
. 1 13
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3.4.2 Evidence of other non-competitive root interference. . . . . . . . . . . . . . . . . . . . . . 1 1 5
3-4.3 Ecologically significant plant traits. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . ...... 1 1 9
�
3. .4 Summarising comments.......... ........ . .................. ................. . . . . . . . . . . . . . . . . 1 20
\
xiii
CHAPTE R FOU R
THE EFFECTS OF SOIL PH OSPHORUS SUPPLV
AND DEFOLIATION ON THE .INTER- AND INTRASPECIFIC
ROOT INTERFERENCES OCCURRING IN MINI-SWARDS
OF BROWNTOP AND WHITE CLOVER GROWN
AT ADEQUATE TO LUXURY LEVELS OF SOIL P SUPPLY
Page
4.1 Introduction
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4.1.1 Objectives............................................................................................... 122
4.2
Materials and methods
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4.2.1 Experimental design and treatme nts................................................ 123
4.2.2 The soil...................................................................................................123
4.2.3 Waterinq................................................................................................. 126
4.2.4 Plantinq..................................................................................................126
4.2.5 Aerial partitions.....................................................................................1.26
4.2.6 Basal nutrients.............................................. : .......................................126
4.2.7 Injection of carrier-free radioactive phosphorus............................ 126
4.2.8 Harvesting.............................................................................................127
4.2.9 Counting radioactive phosphorus-32 and -33 .
..
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4.2.1 0 Frequency distributions of normalised activities of radioactive
phosphorus-32 and -33 ..
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4.3 Results
..................................................................................................................
4.3.1 Effect of species association on phosphorus isotope
. ..... .. . ... . . .. . . .
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acquisition
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. 128
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4.3.2 Effects' of defoliation of outer plants on acquisition of radioactive
phosphorus isotopes by central indicator plants............................. 128
4.3.3 Dry weights and phosphorus concentration of shoots of
131
central indicator plants . . ... . . .. . . . ... .. . . ..... . . .... .
4.3.4 Nitrogen concentration in shoots.......................................................131
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xiv
Page
4.3.5 Dry we ig hts. a nd p hospho rus a nd n itroge n co ncentrat io n o f. root
sutrsamples
1 32
1 32
............................................ ..................... . . ........................
4.3.6 P depletio n zonesarou nd roots
...............
4.4 Discussion
.
................ . ............... . . .......
..........................................................................................................
1 34
4.4. 1 Evidence o f root compet it io n fo r P
1 34
4.4.2 No n-competit ive interfe rence............... ... ...................... ............ .... ...... 1 34
.......................... ...........................
4.4.3 Re lat ive importa nce o f interfe re nces occu rring betwee n b rowntop
.
.
1 35
:............. .................. ................. ............... 1 38
a nd white c lo ve r in the fie ld
....
4.4.4 Summa ris ing comments
......
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XV
C HAPTE R FIV E
TH E EFFECTS OF ADEQUATE TO LUXURY LEVELS
OF SOIL P SUPPLV ON THE
INTER- AND INTRASPECIFIC ROOT INTERFERENCES OF
INDIVIDUAL PLANTS OF BROWNTOP AND WHITE CLOVER
GROWN IN POTS
Pa g e
5.1
Introduction
5.2
Materials and methods
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141
5.2.1 The soil. ...................................................................................................141
5.2.2 Measurement of nitrate and ammonium ions in the soil................145
5.2.3 Planting ...................................................................................................145
5.2.4 Watering..................................................................................................146
5.2.5 Basal nutrients.......................................................................................146
5.2.6 Spraying.................................................................................................146
5.2.7 Harvesting..............................................................................................147
5.2.8 Measurements.......................................................................................147
5.2.9 Analysis of data.....................................................................................147
5.3
Results
.....·.................................................................. . . . . . . . . . ..................................
149
5.3.1 Response of central indicator plant to P appl ication ...................... 149
5.3.2 Inter- and intraspecific associations ..................................................149
5.3.2.1 Shoot dry weight of central indicator olant ..
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5.3.2.� Root weir;hts of central indicator olants
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5.3.2.3 P concentration in shoots of central indicator olant
. 152
5.3.2.4 P content in shoots of central indicator olant
. 154
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5.2.3.5 N concentration in shoots of central indicator olant
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xvi
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5.3.3 P responses o f mo nocultures: effect of pos it ion in pot. .
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5.3.4 N concentrat io n in the soil.. .......... ................. . .. . . .. . . . . . . . . .. . ..... . . . . . . .. . ...... 1 60
......
5.4 Discussion
..........
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1 68
5.4. 1 I nterfe re nce between browntop a nd white c lo ve r . . . . . .. . . . . . . . . .. . . .. . . . . .. 1 68
5.4.2 The competit ive sett ings des ig n
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..........
. 1 69
5.4.3 Su mma ris ing com ments. ............. ................... ....... . . . . . . .............. .......... 1 72
xvii
CHAPTE R SIX
SUMMARY AND CONCLUS IONS
Page
6.1 Overview
..............................................................................................................
6.2 Plant strategy
.................................................................
.
.................................
174
176
6.2.1 Evidence of root competition between browntop and
whtte clover..........................................................................................178
6.2.2 Evidence of non-competitive root interference
...........................
.
....
Other facto rs affect ing interference betwee n browntop and
.
.
white clover
179
6.3
............. ............ . . ...........
...........................................
.....................
Useful ness of techniques to investigate the nature of root
interferences
.
.
. .... .. . .. . .. ... . . .
.
181
6.4
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........... . ...
...
.
.
.
..
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6.5 Suggest ions for furt her work
. ................................... ........................
6.6
:�onclud ing comments .
.
REFERENCES
.....
APPENDICES
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.183
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185
186
. . . ....187
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. 212
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xviii
LIST OF FIGURES
Page
Figure 2.1
Actual and fitted response of dry weights of shoots of (a) browntop and (b) white
clover grown in monoc ultures on Ram iha subsoil to P application as
m onocalcium phosphate. Val ues for Mitscherlich coefficients of fitted cu rves are
given in Table 2.1........................................................ ....................................... ... ... . 55
.
.
Figu re 2.2
Relative yield responses of dry weights of shoots of browntop and white clover
g rown in monocultures on Ramiha subsoi l to P application as monocalc i u m
phosphate, calculated from the fitted Mitscherlich response cu rves . . . . . . . . . . . . . . . . . . 57
Figure 2.3
Effect of application of P as monocalcium phosphate to Ramiha subsoil on the
P concentration in shoots of browntop and white c lover grown in
monocultures.............................. ............ ............................. ......................................... 6 2
Figure 2.4
Resp onse of P concentration in til lers, rhizomes, and roots of browntop grown
in m.onoculture to P application as monocalcium phosphate to Ram iha
subS oil .................................... ............... .... ......... ........... ................ .............. . ...... ... 65
.
.
.
.
.
..
.
Figure 2.5
Effect of application of P as monocalcium phosphate to Ram iha subsoil on the
P concentration in roots in of browntop and white c lover grown in
m onocultures .................... .................................... ........................................................ 66
Figure 2.6
Effect of application of P as monocalcium phosphate to Ramiha subsoil o� the
N concentration in shoots of browntop and white clover plants grown in
monocultures ... .. ..... . ....... . . ............................ ...... ... ...... .................................. .. 6 7
.
.
...
.
.
.
.
.
.
.
.
xix
Page
figu re 2.7
Effect of application of P as monocalcium phosphate to Ram iha subsoil on the
N concentration in tillers and rhizomes of browntop plants grown in
monocultures . .. . ...... ........ .... .... ......... ... .... ..... ........ ....... .... . ............ . .. ........ 67
.
..
.
.
.
.
.
..
..
...
.
.
.
.
..
.
Figure 2.8
Effect of application of P as monocalcium phosphate to Ramiha subsoil on the
N concentration in roots of browntop and white clover plants grown in
monocultures...................... .......................................................................................... 68
Figu re 3.1
The planting arrangement of ramets of browntop and wh ite clover, detailing
position ing of points of P isotope injection, aerial partitions, and the soil
partition u sed to separate the tray into two harvests....... ................................. . . . . . 82
Figure 3.2
Norm alised activities (x1 Q-5) per g of shoot dry weight of P isotope absorption
from soil space shared with browntop and white clover by central indicator
browntop plants, (a) 7 days (harvest one), and (b) 14 days (harvest two)
'
followin g �h e imposition of defoliation treatment and P isotope injection . . . . .- .... 9 3
\
I
Figu re 3�3
Normalised activities (x1 Q-5) per g of shoot dry weight of P isotope absorption
from soil space shared with browntop and white clover by central indicator
white clover plants, (a) 7 days (harvest one), and (b) 1 4 days (harvest two)
following the imposition of defoliation treatment and P isotope injection . . . . :.. 94
.
Figure 3.4
Effect of defoliation treatments on normalised activity (x 1 Q-5)/g in shoots of
browntop plants in the ou�er simulated sward, (a) 7 days, and (b) 1 4 day�
following i mposition of the defoliation treatments and P isotope injections.
Activity data given for P isotope injected into browntop side only. . .. . . . . . . . . . . . . . . . .. 96
XX
P age
Figure 3.5
Effect of defoliation treatments on the total normalised activity (x1 o-5) in shoots
of browntop plants in the outer sim u lated swards, (a) 7 days, and (b) 1 4 days
fol l owing imposition of the defoliation treatments and P isotope injections.
Activity data given for P isotope injected into browntop side only . . . . . . . . . . . .. . . . . . . . . . 97
Figure 3.6
Effect of central indicator species and P application, as m onocalcium
phosphate, to Ram iha subsoil on the root density of (a) outer sward browntop
plants, and (b) outer sward white clover plants at the first harvest.. ....... . . ......... 1 00
Figure 3.7
Effect of central indicator species and P application, as m onocalcium
phosphate, to Ram iha subsoil on the root length per pot of (a) outer sward
browntop plants, and (b) outer sward white clover plants at the first
harvest.
......................................................................................................... ..............
1 01
Figu re 3.8
Effect of central indicator species and P application, as monocalcium
phosphate, to Ramiha subsoil on the specific root length (m/g root fresh weight)
of (a) o uter sward browntop plants, and (b) outer sward white clover plants at
'
the first harvest. Root fresh weights were used to calcu late specific root length
because root dry weights were not available.. ........ : ............................. ....... ......... 1 02
Figu re 3.9
The effect of P application, as monocalcium phosphate, on the zone of soil
exploitation around roots of browntop and white clover plants in the outer
sim u lated swards at the first harvest.. ....... .............................. .......... ........ .. ............ 1 03
Figu re 3. 10
,
The effect of P application, as monocalcium phosphate, on the predicted time
taken for P depletion zones around roots of browntop and white clover in the
o uter simulated swards to overlap, calcu lated from root densities and soil P
buffer capacity ............................................................................. ................................ 1 04
,_
xxi
P age
Figu re 3. 1 1
Effect of P application on the root volume of (a) browntop, and (b) white clover
plan ts in the central indicator and outer simu lated sward positions for the first
1 05
harvest.
..........................................................................................................................
Figur e 3. 1 2
Effect of P application o n shoot dry weights of central indicator plants of
browntop and white clover for (a) the first harvest, and (b) the second
harvest .
..................
.
.
.
. ..... . .......
.
..
........... .
...............
.
.............
.
.......
..
.
. ...........
.
.....
... .
.
.
.
. .....
1 08
Figure 3.1 3
Effect of P application o n root dry weights of central indicator plants o f browntop
and white clover for the first harvest..
...........................................
. ..........................
1 09
Figure 3. 1 4
Effect of P application on the root:shoot ratio of central indicator plants of
browntop and white clover at the first harvest.. ............. ................... . . . . . . . . . . . . . . . . : .... 1 1 0
Figure 3. 1 5
Effect of P application on (a) the P concentration and (b) P content i n shoots of
central indicator plants of browntop and white clover at the first harvest. . .
...
I
...
111
'
'
I
Figure 3. 1 6
Effect o f P application on the N concentration i n shoots of central indicator
plants of browntop and white clover at the first harvest..
:.............................. 1 1 2
....
..
Figure 3. 1 7
Possibl e inter- and intraspecific allelopathic root interactions occur ring within a
browntop-white clover sward; (a) white clover autotoxic with inter- and intraplant toxicity, (b) white clover autotoxic with intra-plant toxicity, and
.
(c) browntop produces chemical that is stim u lative to white clover, i.e., interspecies stimulation
... .
117
.........................
. ..........................................................
.....
........
xxii
Pa g e
Figure 4.1
P lanting arrangement of ramets of b rowntop and white clover i n t h e half-tray,
showing positioning of aerial partitions and points of injection of radioisotopes.................................................. ...................................................................... 1 24
Figure 4.2
Effect of outer simu lated sward species on P isotope acqu isition (normalised
activity x1 o-5/g) by central indicator (a) browntop, and (b) wh ite clover plants, 4
days following the imposition of defol iation treatments and P isotope
injection
1 29
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .
Figure 4 .3
Effect of defoliation of outer sim ulated swards on the total P isotope u ptake
( normal ised activity x1 0·5fg) from both sides by central indicator (a) browntop,
and (b) white clover plants, 4 days following the im position of defoliation
treatments and P isotope injection ........ .................................... .......... ........... ......... 1 30
Figu re 5. 1
P lanting com binations of ramets of browntop and white c lover, showing the
three types of root associations between the central indicator plant and outer
plants, and the positioning of the aerial partition ................. . . . . . . . . . . . . ..................... 1 42
1
Figu re 5.2
Side view of pots for the planting combination 4 (Figure 5 . 1 ), al lowing
intraspecific root interactions to occur between a central indicator browntop
plant and four outer browntop plants, showing the transplantation of the central
indicator plant 26 days after planting ....................... .............. ................................. 1 43
Figure 5.3
Effect of root associations with outer plants on the response of shoot d ry vyeight
of the central indicator (a) browntop, and (b) white clover plant to P appl ication
as monocalcium phosphate .......................................... ....... .... ..... ........................... 1 50
xxiii
Page
Figu re 5.4
Effect of root associations with outer plants o n the response of P concentration
i n shoots of the central indicator (a) browntop , and (b) white c lover plant to P
applicatio n as monocalciu m phosphate
.
.
1 51
. .. . . . . .
. . ...... ............................ .....
.... ..........
Figure 5.5
Effect of root associations with outer plants on the response of P content in
shoots of the central i ndicator (a) browntop, and (b) white clover plant to P
application as monocalciu m phosphate
.
1 55
...........
. . . . ............... ...... .. . ................ ........
Figu re 5.6
Effect of root associations with outer plants on the response of N concentration
in shoots of the central indicator (a) browntop, and (b) white clover plant to P
application as monocalcium phosphate ............... ........ ................................ .......... 1 56
Figu re 5.7
Lines of best fit to describe responses of the s hoot dry weight of the central
i ndicator (a) b rowntop, and (b) white clover plant to P applied as monocalciu m
phosphate to Ramiha topsoil. Details of s lopes of lines and comparisons of
s lopes are given i n Tables 5.1 and 5.2, respectively
.
1 57
.... ........
. . . . . . . . . . . . . . . . . . . . . . ........
\
Figure 5.�
Effect of root associations with the central indicator plant, either browntop or
white clover, on the response of shoot dry weights of the fou r oute r plants of (a)
browntop, and (b) white clover to P application as monocalciu m
phosphate
1 61
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F igu re 5.9
Effect of root associations with the central indicator plant, either browntop or
white clover, on the response of the P concentration i n shoots of the four outer
plants of (a) browntop, and (b) white clover to P application as monocalcium
phosphate
.
.
1 62
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .
. . . . . . .. . . . . . .. . . .. . . . .
......
xxiv
Page
Figure 5. 10
Effects of root associations with the central indicator plant, either browntop or
wh ite clover, on the response of the P content of shoots of the four outer plants
of (a) browntop, and (b) white clover to P application as monocalci u m
phosphate
. . . . . . . . . . . .................. . . . . . . . . .. . . . . ........ . . . . . . . ......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .
1 63
Figure 5. 1 1
Effect of plant position on the response of shoot dry weight per plant of (a)
browntop, and (b) wh ite clover plants grown in monocultu res, to P appl ication
as monocalcium phosphate
.
. 1 64
.............. .... ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .
..
Figure 5. 1 2
Effect of plant position on the response of P concentration in shoots of (a)
browntop, and {b) white clover plants grown in monocultures, to P appl ication
as monocalcium phosphate
.
1 65
.......................... ......... ................
. . . . . . . ........... . . . . . . . . . . . .....
Figure 5. 13
Effect of plant position on the response of N concentration in shoots of (a)
browntop, (b) wh ite clover plants grown in monocultures, to P application as
monocalcium phosphate ..... ........................ .................... .... : ........................ ............. 1 66
\
XXV
LIST OF TABLES
Page
Table 1 . 1
Root properties of browntop and white clover plants grown on sand in pots in
the glasshouse, with basal n utrients supplied (Evans 1 977) . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Table 1 .2
Primary strategies of plants found in habitats of h igh and low stress and/or
disturbance (from Grime 1 979).................. ............................................................... 35
Table 2.1
Coefficients of the fitted Mitscherlich curves for shoot dry weights of browntop
and white clover, including t test comparisons between the coefficients for the
two species...................................................................... ........... .................................. 56
Table 2.2
Effect of P application as monocalcium phosphate to Ramiha su bsoil on the dry
weights of tillers and rhizomes of browntop grown in monoculture. . . . . . . . . . . . . . . . . . . 5 8
Tab le 2.3
'
Effee;:t of application of P as monocalcium phosphate to Ramiha subsoil on the
root:shoot ratio of browntop and wh ite clover plants grown in
'
monocultu res .. :........................................... ...............................................................
61
Table 3. 1
Activities of 32p and 33p in the total 0.9 ml of diluted stock solutions injected into
each sub- plot, at the time of P isotope injection . ............... . . ........ . ....... ..... ... 88
.
..
.
.
...
..
Table 4.1
Effect of P applicati9n as monocalcium phosphate o n shoot dry weight, a � d P
and N concentrations in shoots of central indicator browntop and wh ite clover
•.
plants
. . . . . . . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . ................... . . . . . . . ........... . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . .
1 33
xxvi
Pa g e
Table 4.2
Effect of P application as m onocalcium phosphate on root sub-sample dry
weight, and P and N concentrations in root sub-sam ples of central indicator
browntop and white clover plants
. ....... . . . ... ..... ... .. ... . . ..... . ::: .. 1 33
. .......
...
.
. .
....
..
..
. .
...
...
..
.
...
Table 5. 1
Effect of root association with with outer species and P supply on the fresh
weights of roots (g) of centra� indicator plants .
................
. . . .
. . .
. . .
...
.....
..
.
.....
. .... .'..... 1 53
.
Table 5.2
Coefficients for equations of lines of best fit for responses of dry weight of
shoots of central indicator browntop and white clover plants, grown on Ramiha
topsoil, to P applied as monocalcium phosphate . . ... . . ..
.
..
.
.
. . .
.....
.
. ......
...
.
.
....
..
....
.... 1 58
Table 5.3
t-tests to compare whether or not slopes (m) of lines of best fit are the same for
responses of d ry weights of shoots of central indicator plants, grown in the th ree
root association treatments, to P appl ied as monocalci u m phosphate to Ram iha
topsoil. .. .. .
. .
...
. . . .. ... .. . .
... . 1 59
.
.
............
.....
. ............... ........
......................
.
...
.
....
.....
.
....
. ........
....
'
Table 5.4 1
Nitrate levels m easured in Ram iha topsoil, either following incubation of wet
soil for 0 and 3 days, · or sampled after 1 8 days from pots with browntop or wh ite
clover plants g rowing in the soil...
.......
. .
...
....
. .. .... .. . . ..... .... ... ... ....
..
.
.
..
. .
.
.
.
..
.
....
.
..........
. 1 67
xxvii
LIST OF PLATES
Page
Plate 2. 1
Photog raphs of (a) browntop, and (b) white clover plants in the P response trial,
at the time of harvesting
. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
Plate 3. 1
Photographs showing (a) glasshouse view, and (b) close up view of simu lated
sward d ual-labelling trial. Plants were grown at 0 and 1 00 mg P applied/kg soil
in the left and right trays, respectively
83
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......... . . . . . . . . . . . . . . . . . . . . . . . . . .
Plate 4.1
Photograph of trays used to grow simu lated swards, showing separation of tray
into two halves, the left side with browntop as central indicator species, and the
right side with white clover as central indicator species. The tray pictu red above
had outer white clover simu lated sward defoliated
. . . . . . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 25
Plate 5. 1
Photograph showing the positioning of aerial partitions in pots
. . . . . . . . . . . . . . . . . . . . . . . .
1 44
xxv i i i
LIST OF APPENDICES
Page
Appendix 1
P buffer power of Ram iha top- and subsoils
212
. . . ......... . . . . . . ........... . . . . . . . . . . . . . . . . . . . . . . .. . . . . .
Appendix 2
D ry weights, and P and N contents of ramets used for planting in the P
response trial (Chapter Two)
.................................. ........... ......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
214
Appendix 3
P rocedu re for staining vesicular-arbuscular mycorrhiza for rapid assessment of
infection
. . . . .
�. . . . . . .. . . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
215
Appendix 4
M ethod of counting radioactive phosphorus-32 and - 33 in harvested plant
material.
217
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 5
Discussion on rooVshoot ratio data
. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
219