635.52:581.132
MEDEDELINGEN LANDBOUWHOGESCHOOL
WAGENINGEN • NEDERLAND «81-12(1981)
PHOTOSYNTHESIS OF LETTUCE
I. RESULTS WITH CULTIVAR 'AMANDA PLUS'
H. M. C. VAN HOLSTEIJN
Departmentof Horticulture, Agricultural University,
Wageningen, The Netherlands
(Received 11-III-1981)
Publication 480
H. V E E N M A N & Z O N E N B.V. - W A G E N I N G E N - 1981
PHOTOSYNTHESIS OF LETTUCE
I.
RESULTS
WITH
CULTIVAR
'AMANDA
PLUS'
INTRODUCTION
In T h eNetherlands thecultivation ofbutterhead lettuce (Lactuca sativa L.)in
glass-houses takes placeinspring, autumn andwinter, andintheopen field inthe
spring a n d summer season. Fundamental data o n thegrowth of lettuce are
important t oobtain a noptimal yield. Inprevious papers results ofthe growth
analysis (VAN HOLSTEUN, 1980b) a n d ofthe process ofsoil covering of lettuce
(VAN HOLSTEUN, 1980a) were presented. D a t a on photosynthesis of lettuce
plants inrelation with temperature, irradiance andC0 2 -concentration are essential fora good understanding ofthe growth process. Itisknown, for instance,
that inthepoor light period changes intheenvironmental conditions during the
day o r during a number of days strongly affect growth. EENINK (1978)a n d
EENINK a n dSMEETS (1978) concluded from research in thephytotron a n d in
glass-houses that certain genotypes oflettuce reacted rapidly toshort periods of
higher irradiance a n dtemperature resulting in a higher yield, while thesegenotypes gave a similar yield compared to other genotypes under constantenvironmental conditions. Photosynthesis measurements may give additionalinformation on these aspects.
The quantitative growth analysis describes a n danalyses long term growth
aspects (e.g.V A N HOLSTEUN, 1980b; SALE, 1977), while gasexchange measurements permit ananalysis ofshort term effects with either constant or changing
conditions of irradiance, temperature a n d C 0 2 . T h eeffect of irradiance on
photosynthesis of sun and shade plantswas studied bye.g. BJÖRKMANa n d H O L M GREN (1966), B Ö H N I N G a n d BURNSIDE (1956), C H A R L E S - E D W A R D Set al. (1974),
L O A C H (1967) a n d L O G A N a n d K R O T K O V (1968). T h e photosynthesis response
of butterhead lettuce on irradiance was studied by A C O C K a n dH A N D (1974),
BROUWER a n d HUYSKES (1968), GAASTRA (1966), REINKEN et al. (1973) a n d
TATSUMI a n d H O R I (1969). SARTI (1973) presented light response curves of a
coslettucecultivar andV A N HOLSTEUN etal.(1977)investigated thegas exchange
properties ofwhole shoots asaffected by drought.
Gas exchange measurements canbe carried outin various ways. Lettuce
measurements were done onleaf discs (SARTI etal., 1977), attached leaves or leaf
p a r t s ( G A A S T R A , 1966; R E I N K E N et al., 1973; SARTI, 1973) o r whole shoots
( B R O U W E R and HUYSKES, 1968; V A NHOLSTEUNet al., 1977; L O R E N Z a n d WIEBE,
1980; TATSUMI a n d H O R I , 1969, 1970 a n d WIEBE a n d L O R E N Z , 1977). Since most
plants andcrops grow inplant communities orinmore orlessclosed canopiesthe
photosynthesis data ofa singleplant have toberelated toitsposition ina canopy.
Lettuce plants donotform ahomogeneous canopy orrowcrop community and
only during the early stage ofgrowth they canbeconsidered assolitary plants.
Meded. Landbouwhogeschool Wageningen81-12 (1981)
1
Sincethe structure of mature plants iscomplex and the whole shoot of the lettuce
plant isharvested, measurements with whole plants are necessary. In addition
the separation of a bubbled andcurved leaf and inconsequence the gas exchange
measurement ofa single leaf ofa heading butterhead lettucej>lant is difficult.
Equipment forwhole plant measurements isavailable (e.g. LOUWERSE a n d V A N
OORSCHOT, 1969; V A N HOLSTEIJN, 1979).
The photosynthetic and respiratory rates are usually expressed per unit leaf
area ( A C O C K et al., 1978; GAASTRA, 1959, 1966; V A N HOLSTEIJN et al., 1977;
REINKEN et al., 1973) or unit dryor fresh weight ( A C O C K et al., 1979; BROUWER
andHuYSKES, 1968; CHARLES-EDWARDS et al., 1974; SALE, 1977). BROUWER a n d
HUYSKES (1968) expressed thephotosynthetic rates oflettuce also onunit exposed leaf area (soil cover). Field chamber and assimilation chamber dataare
usually expressed onunit ground area ( A C O C K etal., 1978;ALBERDAetal., 1977;
M C C R E E a n d T R O U G H T O N , 1966; SALE, 1977).
Differences inthenumber of leaf layers, leaf thickness orchlorophyll content
stillcan interfere acorrect comparison of the effects of environment a n dvariety.
BJÖRKMAN (1968) therefore related thesoluble protein to photosynthesisa n d
CHARLES-EDWARDS et al. (1974) a n d PATTERSON et al. (1977) measured the
mesophyll tissue volume. The latter authors a n dKOLLER a n d DILLEY (1974)
presented photosynthesis data per unit chlorophyll. Other parameters as basesof
expression with specific advantages a n ddisadvantages for a comparison of
photosynthetic results arefeasible. Inthis paper, therefore, attention ispaid to
this problem with theresults ofthebutterhead lettuce cultivar ' A m a n d a Plus'.
Theory
Empirical a n dsemi-empirical models have been applied t o describe the relationship between environmental factors a n dphotosynthesis of single leaves
( A K I T A et al., 1968; C H A R L E S - E D W A R D S a n d L U D W I G , 1974; M A R S H A L L a n d
BISCOE, 1980; PEAT, 1970; THORNLEY, 1976). THORNLEY (1976) modified single
leaf models forthe use ofcrop photosynthesis data and A C O C K etal. (1976b)a n d
D U N C A N et al. (1967) used canopy models derived from leaf models. These
models describing the gasexchange of a plant orcanopy giveagood understanding ofthe gasexchange properties ofa plant community ( A C O C K etal., 1976a,
1976b; C H A R L E S - E D W A R D S a n d A C O C K , 1977; D U N C A N et al., 1967; E N O C H a n d
SACKS, 1978; TOOMING, 1967), ofthevarious physiological processes involved,
and of the data which are still lacking.
TAKAKURA (1975)tested hismodel forplant growth optimisation by computer
with lettuce plants, and SORIBE a n d CURRY (1973) simulated lettuce growth ina
plastic greenhouse, b u tinformation regarding leaf or plant photosynthesis of
lettuce wasa n dis still lacking and hence appropriate models arenot available.
THORNLEY (1976) described a rectangular hyperbola relating the gross photosynthetic rate of a leaf to both irradiance a n d C 0 2 :
P
2
.%TTTc
Meded. Landbouwhogeschool Wageningen 81-12(1981)
inwhichP gisthegrossphotosynthetic rate,Ithelevelofirradiance,Cthe carbon
dioxide concentration, a the initial slope of the P-I-curvei.e. the photochemical
efficiency and T the initial slope of the P-C-curve i.e. the leaf conductance for
C 0 2 transfer. Maximum grossphotosynthesis (Pm,g)isTC(I = oo)oral (C= oo).
The net photosynthetic rate (Pn) isobtained as the difference between the gross
photosynthetic rate and the dark respiration (R d ):
P
s -
R
d
otl-üC
od + xC
= 3 ^ 7 T -
R
(2)
d
and themaximum netphotosynthesis, P m n , (I= oo)isTC- Rd and P m n(C= oo)
is otl - R d . ACOCK et al. (1976b, 1978) used this equation as a basis for their
canopy model for green peppers and tomato, which model gave good estimates
for thevaluesofa and x.Thephotorespiration (R,) isnot included asa separate
component in thisequation, as isdone in almost similar models used by ACOCK
et al. (1976a), CHARLES-EDWARDS et al. (1974).and CHARLES-EDWARDS and
LUDWIG (1974).When equation (2)isusedinaplantmodel,theparametera will
present the'plant photochemical efficiency' andxthe'overallplant conductance
for C 0 2 transfer'. The photosynthesis-irradiance response curve can be written
as:
aI P
P = P + R ^-d
a« I_J5i*l_
+ P m,g,i
(3)
Thegrossinitialslopeofthecurveisag(I = 0)and thenetinitialslopeocn(I = Ic).
Ic, the light compensation point when P n = 0, is
«g (Pm,g,i -R d )
Rd can either be measured and used for the calculation of other parameters or
estimated from the equation.
The photosynthesis-C0 2 response curve can be written as:
P P +R
« = " <= 'rlT
(4)
(5)
Thegrossinitial slopeof theC0 2 -photosynthesiscurveist g (C = 0)and the net
initialslopeTn(C = CC).CC,theC 0 2 compensationconcentrationwhenP n = 0,is
\
R
P
^d
^m.g.c
(Pm,g.c - Rd)
(6)
NotethatRdinequations3and4representsanothervaluethaninequations5and6.
In the ideal situation when all the light quanta are absorbed and used for the
reduction ofC 0 2 asingleconstant valuefor thephotochemical efficiency (<xg,con)
could be obtained for at least all C 3 -plants. RABINOWITCH (1951) and GAASTRA
Meded. Landbouwhogeschool Wageningen81-12 (1981)
3
(1962) concluded from their analysis of the photochemical processes that the
maximum lightefficiency should beabout thesameforleavesofdifferent species
and for leaves grown under various environmental conditions. CHARLESEDWARDS et al. (1974) found no significant differences between photochemical
efficiencies (ocn)ofsixtemperate grassvarieties. LOUWERSEand VAN DE ZWEERDE
(1977)alsoobtained similarvaluesofagofvariousgroupsofbeanplants. ACOCK
et al. (1976b) observed similar values of ocn between leaves measured under
various circumstances andconcluded that their data supported theconcept ofa
constant potentialphotochemical efficiency forthephotosynthesis ofC 3 -plants.
However, this potential value (ocg con) is never obtained due to limitations of
externalC0 2 -concentration,conductanceforC 0 2 orphotorespiration. Measured differences between the initial slopes of the P-I-curves (e.g. BÖHNING and
BURNSIDE, 1956; PEAT, 1970;for lettuce: BROUWER and HUYSKES, 1968; SARTI,
1973) aredueto differences in structure and morphology of theleaf, plant or
canopy.
With acorrection factor allmeasured or estimated values ofocgcanbe made
equal toocgcon. This means that correction isnecessary either for the measured
irradiance (Wm" 2 ) orforthemeasured gasexchange rate.Thecorrected value
for the irradiance (Icor) will be expressed in Watt per plant (WP1 -1 ) andthe
corrected valueforthephotosynthesis (Pcor)onthebasisoftherealeffective leaf
area (EL)ofthe plant. This area, EL(m 2 Pl _1 ),intercepts andabsorbs all light
quanta withefficiency agcon.Insuchaconcept thenumber ofleaf layersandthe
leafthicknessoftheplantareincorporated, whereasELgivesinformation onthe
morphology oftheplant. Thephotosynthesis perplant P(mgC 0 2 P I - 1 s~*),
expressed onthebasisofeffective leaf area,isnowdescribed by: P cor = P . E L - 1
(mg C 0 2 m " 2 s" 1 ) and Icor by I.EL.
The efficiency otgcon (mg C 0 2 J" 1 ) is defined by:
d(P/EL)
dl
dP
d(Pcor)
dl
ddcor)
1= 0
2
L
:0
EL
(7)
1 =0
l
withocg(mgC 0 2 m PI"*J" ) calculated from theobtained plantdata.Theconclusion from (7)isthat EL = ocg/ag con (m 2 PI - 1 ). Thephotosynthetic rateper
effective leafarea(P.EL~ x )isP ,.ocgcon .a~ 1•Theeffective leafareaisequaltok.A
or k'.S,or another basis of expression for photosynthesis (k andk' constant).
According to GAASTRA (1966) the calculated value of ocgfor lettuce variesbetween 4 and 14% of the a gcon .
A similar theory isvalid when, instead of gas exchange data perplant, data
expressed perunit leaf area or soil cover areused. Thephotosynthetic rateper
effective leaf area will be equal to Pi-agjCOna~giV or Ps.ag con.a ~[ with ag>1
and <xgscalculated on leaf area or soil cover basis, respectively. Photosynthetic
ratescanthen becompared using acorrection factor E L " 1 , whilethemeasured
levelofirradiance inW m - 2 canbeused. Note that thecorrected value ofI c will
be IC.EL = lcug.aJon.
Meded. Landbouwhogeschool Wageningen81-12 (1981)
In thispaper theanalysisoftheresultsofgasexchangemeasurements isbased
on theaboveexplained theory with theuseofthecorrection factor E L " 1 for the
photosynthesis data or EL for the irradiance data.
MATERIALS AND METHODS
Twoexperimentswerecarried outwiththebutterhead lettucecultivar 'Amanda Plus', one in spring (nr. 1)and onein autumn (nr. 2).Experiment 1included
plants of two sowing dates (la and lb) with different age groups A, B and C
based onweightand leafarea. Theleafarea ofplantsofageAvariesbetween 4.5
and 11.5dm 2 and the corresponding dry weight between 0.55 and 1.60 g. These
values are for plants of age Bbetween 14.0and 28.5dm 2 and between 1.70 and
3.90 g and for age C between 31.0 and 43.5 dm 2 and between 3.95 and 7.45 g.
In bothexperimentsplants ofdifferent habitus wereobtained with 4 different
pretreatments ofirradiance and temperature (Table 1).'Amanda Plus'had been
used also in previous experiments of growth and photosynthesis (VAN HOLSTEIJN, 1980a, 1980b; VAN HOLSTEIJN et al., 1977).
OnJanuary 17seedsoftheplantsofexperiment 1aweresowninpeat blocksof
5 x 5 x 5cm in a glass-house at an average day/night temperature of 19°C.
After germination the average day/night temperatures were 17/12°C, respectively. On January 24 the plants were selected. After that 11 hours artificial
illumination of 35Win" 2 (400-700 nm at plant level;HPLR lamps400W)was
TABLE 1.Data about the 4treatments ofexperiments la, lb, and 2with butterhead lettuce cultivar
'Amanda Plus'. Day and night temperatures are mean temperatures and the observed levels of
irradiance are also mean levels. NI is natural daylight and AI additional illumination with HPLR
lamps.
Experiment
Treatment
Temperature (°C)
day
night
Irradiance (Wm 2 )
la
(age B and C)
I
II
III
IV
17.0
17.0
26.5
26.5
12.5
12.5
17.5
17.5
NI + A l ó ó W m 2 117.5
70% of NI
: 36.0
NI + AI 69 W m ^ 124.0
70% of NI
: 38.5
lb
(age A)
I
II
III
IV
18.0
18.0
27.0
27.0
12.0
12.0
18.0
18.0
NI + A I 6 6 W m " 2
70% of NI
:
NI + AI 69Wm"2.
70% of NI
:
2
I
II
III
IV
16.5
16.5
26.0
26.0
12.0
12.0
20.0
20.0
N I + A I 6 6 W m " 2 84.5
70% of NI
: 13.0
NI + A I 6 8 W m - 2 87.0
70% of NI
: 13.5
Meded. Landbouwhogeschool Wageningen81-12 (1981)
117.0
35.5
123.5
38.0
given. On February 18plants were again selected and transplanted into 1.6 litre
pots.Inpreliminary experimentsithad beenestablished thatgrowth of'Amanda
Plus' and other butterhead cultivars until a fresh weight of 150 grams was
undisturbed inthesepots. On March 4(= day 0)theplants were separated in 4
groups (I, II, III and IV) and different temperatures and irradiance levels were
induced (Table 1).The HPLR lampsproviding the additional illumination were
situated 1.2.meter above plant level. Fertilizers were applied according to the
recommendations oftheLaboratory for SoilandCropTesting,Oosterbeek, The
Netherlands. Pirette wassprayed twiceagainst diseases.Gasexchange measurementswith plants of the 4treatments ofexperiment la (age Band C) started on
day 10 and ended on day 27.
Plants of experiment lb (age A) were sown on February 22and transplanted
on March 22.On March 23(day 19)theseplantswerealsoseparated in4groups
(I, II, III and IV; Table 1).Gas exchange measurements started on day 28 and
finished on day 36. The plants of experiments la and lb were used for
photosynthesis-irradiance response measurements.
On September 30seedsof'Amanda Plus'weresown for experiment 2inwhich
thesameprocedurewasapplied asinexperiment 1.Theaveragetemperature was
20°C.After 5daystheday/nighttemperatureswere21.5/16°C,respectively,until
October 31. After October 9 artificial illumination (30 Wm~ 2 ) was applied
during 11hours. The plants were transplanted on October 24 and 9days later
distributed between the treatments I,"II, III and IV (Table 1).During thecultivation period TMTD was sprayed 3 times. Gas exchange measurements for
photosynthesis-C0 2 responsecurveswerecarried outbetweenNovember 21and
December 16.Temperature and irradiance in the glass-house were measured as
in previous experiments (VAN HOLSTEIJN, 1980a).
For the photosynthesis measurements the closed system asdescribed by VAN
HOLSTEIJN (1979) was used. The pot, containing the root system, was airtight
sealed from theupper part of theplant and placed inacylindrical perspex plant
chamber (height 34or 44cm;diameter 44cm). In thecentre of thechamber the
windspeed was0.8m s"' and the relativehumidity 75to 85%.The temperature
inthechamber near theplant wasmeasured by thermocouples. The light source
above the plant chamber consisted of 5HPLR lamps (400 W) and the level of
irradiance could be reduced by movable screens with a different number of
perforations. The irradiance (maximum value 215 Wm~ 2 ) was measured on
plant levelwithselenium photocells.TheC0 2 -concentrationwasmeasured with
an infrared gasanalyser, while the transpiration was not registered at that time.
Inexperiments la and lb response seriesconsisting of 8irradiance levelswere
carried outinasequence from maximum available irradiancetodarkness. These
series lasted 2to 3hours and were determined at 14° and 26°C. Sixty minutes
after insertingtheplantintotheplantchamber theactualmeasurements started.
Gasexchangereadingsweretakenintherangebetween580and 500mgC 0 2 m" 3
when a constant response was reached. Plants of similar size or weight were
always selected for the two replicates.
In experiment 2 the response series were determined at 15° and 25°C at the
6
Meded. Landbouwhogeschool Wageningen81-12 (1981)
irradiance level of 142Wm~ 2 (for treatment I and III) and at 65Wm~ 2 (treatment II and IV) in the closed system according to the procedure described by
NILWIK (1980b).The measurements started at a C0 2 -concentration of 1400mg
m " 3 and lasted 2 to 3.5 hours, after which period the C 0 2 compensation
concentration was reached. At least 8readings per C0 2 -series were taken with
threereplicatespertreatment.Data at 15°Cconsisted ofplantsoftreatmentsI,II
and III and at 25°C of treatments I, III and IV.
The data of fresh weight and leaf area were collected immediately after the
measurements.Thedryweightoftheplant wasobtained bydryingduring 7days
inaventilated oven at 65°C.Onehour before themeasurements threephotos of
the plant were taken. The soil cover area was calculated from one photo from
above and theprofile area ofaplant from the average oftwophotos from aside.
According to equations (3) and (5) regressions were calculated through the
photosynthesis data per plant from which the photochemical efficiencies ocgand
ocn, thenetplantconductance (xn),themaximalgrossandnetphotosynthesis P mg
and P m n , the dark respiration (R d ), the light compensation point (Ic) and the
C 0 2 compensation concentration (Cc) were obtained. These calculations were
carried out on a desk calculator HP 9518Awith the actual program outlined by
NILWIK (1980a). The Tukey's Honest Significant Difference was calculated to
compare the calculated results of the different treatments (CARMER and SWANSON, 1973).
RESULTS
In Figure 1 an example of a response curve of the net photosynthesis to
irradiance isgivenofplants oftreatments I,II,III and IV,measured at 14°C and
an external C0 2 -concentration of about 560mg m" 3 . The photosynthetic rates
are expressed per plant (a), unit leaf area (b), unit soil cover (c) and unit dry
weight (d). The values of the initial slopes, the photosynthetic rates and dark
respiration thus depend on the applied unit. The sequence from high to lower
levelsofphotosynthesisbetweenthefour treatmentsisalmostthesamefor figures
la,band c(e.g.I,III,II and IV),althoughthedifferences between thecurves are
varying. When the photosynthesis is expressed per unit dry weight (Id) the
sequence is II, I, IV and III.
InTable 2various parameters, calculated from measured data of experiments
la and lb, are presented. Values of the P-I curves were calculated from regressions through 8points and the values of the replicates were taken together.
Tukey's Honest Significant Difference (CARMER and SWANSON, 1973) is calculated per age (A, B and C) and for all data together.
Except for thedata of Icacomparison ofthe results,especially those ón plant
basis,isdifficult. Ingeneral,however,thevaluesofocgincreaseand ofagdecrease
with an increase of age. The values ofotgand ocg of treatment IV are lower than
other values when measured at 14°C, while those differences disappear when
measured at 26°C. In general, the maximum gross photosynthesis on leaf area
Meded. Landbouwhogeschool Wageningen81-12 (1981)
1
TABLE 2.Parameters describing the response of grossphotosynthesis (Pg)to irradiance (I) for the 4
treatments (I,II, III and IV) ofthegroups A, Band C ofexperiment 1.Measurements were carried
out at 14°and 26°C and at an external C0 2 -concentration of about 560(14°C) and 545(26°C) mg
m"3.ot anda g :photochemicalefficiencies(inl =0)expressedperplant(mgCO 2 m 2 Pl~'J~ l )andperunit
leafarea(mgC 0 2 J"');P m gandP.J,g:maximumP gatsaturatingIexpressedperplant(mgC 0 2 PI~'
h*')and per unit leafarea (mgC 0 2 dm"2 h_ 1 );Rd:dark respiration per unit leafweight (mg C 0 2
g _ 1 h " 1 ) ; Ic light compensation point (Wm~ 2 ). Specific leaf weight (SLAV)is expressed in g m " 2 .
THSD: Tukey's Honest Significant Difference (p < 0.01).
Treatment
age A
I
II
III
IV
I
II
III
IV
THSD A
age B
I
II
III
IV
I
II
III
IV
THSD B
age C
I
II
III
IV
I
II
III
IV
THSD C
THSD ABC
Results
Temperature
P1
(°Q
103 a g
103 aj
14
0.406
0.323
0.536
0.296
0.238
0.211
0.234
0.488
0.088
4.82
4.37
4.67
2.84
4.54
5.05
4.41
5.33
1.23
179.1
104.2
196.1
103.4
136.6
98.6
178.6
147.1
37.6
0.570
0.778
0.662
0.575
0.326
0.571
0.500
0.542
0.139
3.06
3.05
2.62
2.03
2.55
3.87
3.05
3.16
0.79
0.782
1.004
0.725
0.702
0.628
0.715
0.625
0.786
0.175
0.136
2.30
2.71
1.85
1.69
1.81
2.13
1.60
2.07
0.47
0.87
26
14
26
14
26
P
Rd
Ic
SLW
21.4
13.7
17.2
9.9
26.1
23.6
34.3
16.1
7.1
7.3
8.2
6.1
11.9
18.2
29.6
26.1
18.7
6.5
8.5
7.2
6.2
13.0
19.3
25.2
29.0
13.0
4.3
19.3
13.2
15.8
10.2
17.2
11.4
14.9
11.3
2.8
302.4
254.3
285.5
212.9
520.2
236.4
367.1
241.3
94.7
16.2
9.8
11.5
7.5
41.1
15.9
22.7
14.6
7.6
4.4
5.2
3.5
3.5
11.7
15.5
11.8
16.1
4.1
7.5
6.3
6.1
6.4
22.1
16.1
18.1
17.1
4.3
18.0
12.4
15.6
10.3
16.6
12.5
15.6
10.6
3.7
320.1
351.7
274.9
207.0
520.1
531.1
579.1
456.0
81.8
82.9
9.4
9.4
7.0
5.0
15.0
15.8
15.0
11.9
2.6
6.2
3.5
4.1
3.0
3.6
7.3
9.4
7.1
8.1
2.8
4.9
9.9
5.6
6.8
5.6
25.8
18.6
19.0
16.8
4.1
4.2
21.9
12.8
14.4
8.9
20.8
12.9
14.3
9.9
5.8
4.1
m,g
basisdecreaseswithage.Lettuceplantsgrownatlowertemperaturesorahigher
levelofirradiance showed higher P.J,g-values,whilea hightemperature during
themeasurements alsoresultedinhigherrates.Thecalculated resultsofRdare
wellinagreement with themeasured data (not presented here),the correlation
beinghigh(r = 0.99).Darkrespirationratesonleafweightbasisdecreasedwith
8
Meded. Landbouwhogeschool Wageningen 81-12 (1981)
150
200
Irradiance, Wm-2
250
FIG. 1.Curvesthroughmeasureddatadescribingtheresponseofnetphotosynthesistoirradianceof
the4treatments(I,II,IIIandIV)ofexperiment 1,ageB.Thephotosyntheticrates(mgC0 2h ')are
expressedperplant(a),perunitleafarea(b),perunitsoilcover(c)andperunitdryweight(d).The
measurementswerecarriedoutat 14°CandanexternalC02-concentrationofabout560mgm~3.D
= I; • = II; • = III; o = IV.
increasingageand lowermeasurement temperatures.The Revaluesperplant of
ageAwereintheorderofmagnitude of 14%(at 14°C)and 17%(at26°C)ofPm>g
per plant, with lower percentages at increasing age. The Ic-values depend
stronglyonthetemperaturesduringmeasurements.Thevaluesmeasuredat 14°C,
atemperatureapplied inthepoor lightseasoninglass-houses,arebetween 5and
13 Wm" 2 for all treatments. Differences between the parameters are more
obvious between ageAand Band between ageA and Cthan between ageBand
C. High SLW-valuesare due to low temperatures and a high level of irradiance
during growth.
Theeffective leaf area ofplant, EL, isassumed to berelated with one or more
plant characteristics: EL = ocg.ocg~'on = k.A or k'.S,etc.. A multilinear regressionhasbeencarriedoutbetween<xgonplantbasiswithsoilcover(S),leafarea(A),
averageprofile area(Pa)and dryweight(W)for allplantsofexperiment 1.From
linearregressionsitbecameevidentthatthebestfitof<xgoccurredwithsoilcover.
The Swastaken asthe first independent variable, Aassecond oneand W as the
last one inthemultilinear regression model. Thesame sequence ofplant characteristics was applied in a regression model with growth rate in a previous paper
(VAN HOLSTEUN, 1980b).Theprofile area was listed after leaf area in the model.
Meded. Landbouwhogeschool Wageningen81-12 (1981)
9
TABLE3.Thecorrelationcoefficientsoftheregressionsofthegrossphotochemicalefficiency onplant
basis(ag)withthesoilcover (S),leafarea(A),profilearea(Pa)and leafdryweight(W)for allplantsof
experiment 1 and for the three separate age-groups.
Group
Correlation coefficients (r) of
linear regressionsi of ag
A, B, C
A
B
C
with
the m ultilinear model
S
A
Pa
W
0.93
0.84
0.85
0.66
0.92
0.87
0.79
0.56
0.91
0.86
0.88
0.77
0.44
-
0.90
0.92
0.76
0.62
The correlation coefficients are listed in Table 3. Addition of the Pa to the
multilinear regression of all data did not improve this model (p < 0.01) significantly and therefore Pa was not added to the models per age-group. The
correlation coefficients ofocgwithS,Aand Wdecreasewithincreasingage,while
thiseffect ismorepronounced for thecorrelation ofocgwithAand WthanwithS.
The results of a 3-wayanalysis of variance of thegross photochemical efficiencies, maximal gross photosynthetic rates per unit leaf area, maximal net photosyntheticrates,netphotosyntheticratesatirradiancelevelof35and 100Wm"2and
of the light compensation points are listed in Table 4. According to the theory
presented inthe introduction the photosynthetic rates aredivided by<xgand the
corrected lightcompensation pointsmultiplied bythisparameter. Instead of EL
( = ocg.oc~|con) only the factor a g has been used, since ag con has a constant
value. The values of P n 35 and P n 100 are chosen since these levels of irradiance
correspond with those during cultivation.
For almost all parameters differences between factors age and measurement
temperature exist, while the influence of temperature during cultivation on the
parameters isless.For photosynthetic rates on ag-basisthe differences between
age aremainly due to plants of ageA.The level of irradiance during cultivation
hasalargerinfluence onphotosynthesis thanthetemperature level,asappliedin
these treatments, while temperature during the measurements contributes
stronglytothedifferent maximumrates.Nosignificant difference occursbetween
the P n 35-values of tin four treatments. At a high level of irradiance (100
Wm" 2 ) the temperature during measurements did not affect the net photosyntheticrates.Thecorrected lightcompensation point (Ic cor) ismainlyaffected by
ageand temperature during measurement and not byenvironmental conditions
during growth, while I c is more influenced by the conditions during growth
than by age.
In Table 5the calculated results of the C0 2 -series of experiment 2are listed.
Tukey's Honest Significant Difference (CARMER and SWANSON, 1973)is calculated for alltreatments together. ValuesofthePn-C-curveswerecalculated from
regressions through atleast 8points and thevaluesofthe 3replicateswere taken
together. Thexn-and tj-values ofplants oftreatment Iand III are slightly lower
10
Meded. Landbouwhogeschool Wageningen81-12 (1981)
1
äs
S.s © .g .ts
a c
i*
V I ^ t —'
T t \ó ON
; | *
§.s S
ni Q,
G —
ta
G
>- 1
1
O (N (N (N
c
•a ,— « .2 «
e M
, *J u
i
« s
H eu — S «
» B 1 1 gfc
g d I a •3
s u •3 ~ c ,-v
e« » M
t- 8 o
n
- E
OO O Û0
eu
—
o
.t2 O
g) V
âlll
O ON o rn
' s o,
> ' S S j 3
^
U R S
Où
en O ^ <N
o tt!
BS rfr" vS vS ^O
Ö <u
S3
U II J 3 U
« • " C M
(D 2
vo oo in ON
v-j OO r, n
.a o
ö
- H V~l ^ .—1 .—• —H
O (U o>
B g o h s 'S 3
ON ON
**
oo o
t-- oo
m ON
1—I f—I 1-H
**
o
ON 0 0
ON t - -
ON
^ H
S JU a 'S
oo n TJ- v i
~ - * n o oo
m rn M r i
ÎS O
C «-"
oo oo
5
S
Il ?
Is
•"
«S - _ - S
jl*i
«
«
. OH
e =* •
BO
•c gp
3 J.
<N O f - (N
ON O "3" ^o
Tf ^D v i i n
ooo o
m ri—« o o
* ^ > -*
o2
e
•
3
= O
6.2
„
O
«•o e Sa a
>? c 3 s p
>°
T t V£> Tfr
r-i * n r -
I
"go. 6b
(N m vo
IL)
<"
'S S
O.g
c 'S
.2 S
S .SP
ais
11
• -2P-S
u
i -o £
I oS
3
B
O
Î5
o
o
ja
< mu
S
H Ö
C3
5^
Meded. Landbouwhogeschool Wageningen81-12 (1981)
*2
s
g
"3
VH
00
ai
g. .2ä
S
2
'S
0
C
O
O
S
e
S o
V o
Ui
c
.g
1c
"ë3
a
u
<U cd
>
O
B
Ui
O
UI
Ui
*«
O
11
TABLE 5. Parameters describing the response of net photosynthesis (P„) to external C 0 2 concentration for the4treatments (I,II,III and IV)ofexperiment 2.Measurements werecarried out
at 15°and 25°Cand at 65(for IIandIV)and 142Wm"2(Iand III).Thex„and T'nare conductances
for C 0 2 (inC = Cc)expressed per plant (m 3 Pl"' s " ') and per unit leafarea ( m s " ' ) ; P m , and P^.n:
maximum P n at saturating C expressed per plant (mgC0 2 Pl*'h~ ') and per unit leaf area (mgC0 2
dm" 2 h ]);C c : C 0 2 compensation concentration (mgC0 2 m" 3 ) . Specific leafweightisexpressed in
g m - 2 . THSD: Tukey's Honest Significant Difference (p < 0.01).
Treatment
Temperatuur
(°C)
-
Results
103Tn
10 3 TJ
p
x
m,n
K,n
cc
SLW
I
15
25
0.190
0.136
0.869
0.687
244.6
305.9
11.2
15.6
94.2
176.1
19.9
17.3
II
15
0.110
0.735
104.8
6.7
58.8
11.5
III
15
25
0.260
0.184
1.234
0.906
212.5
270.9
10.1
13.4
101.5
169.1
15.3
16.6
IV
25
0.088
0.378
132.8
5.7
110.2
9.4
0.013
0.214
63.4
3.3
22.9
4.7
THSD
at an increased temperature during measurements and lower temperatures during growth. For plants grown at low irradiance (II and IV) a high temperature
during growth (IV) and/or measurement results in low values of xn and x*.
Temperature affects maximum P n ,resultinginhighervaluesfor P m nand P„Jn at
higher measurement temperatures (for I and III), but lower values when the
temperature during cultivation ishigher (III). The calculated Cc-valuescorrespond with the values registered by theinfrared gas analyser and the correlation
between the calculated and measured values was high (r = 0.97). C c depends
strongly on temperature during measurement.
DISCUSSION
Gas exchange data of whole plants or shoots are more difficult to interprète
than those of single leaf measurements. Special problems arise for butterhead
lettuce due to its short stem and the production of a head with bubbled and
curvedleaves,whichexcludenewformed leavespartlyfrom irradiance (BENSINK,
1971; DULLFORCE, 1968). Moreover, in practice the plants do not grow as
solitary plants.The canopy isnot homogeneous,evennot at narrow spacings at
theendofthegrowthperiod.Theleavesandthenumber leaflayersare unequally
distributed overthe'canopy'. Plantsachieveahigh 'leafarea index'inthe centre
during heading stage,whiletheexterior of theplant consistsof one or afew leaf
layers only. Because of the complex structure of lettuce plants a comparison
betweenplants(e.g. BROUWERand HUYSKES, 1968; VAN HOLSTEIJNetal., 1977)is
difficult. Four treatments were given during cultivation in order to obtain
12
Meded.Landbouwhogeschool Wageningen81-12 (1981)
distinct differences in plant structure and habitus and to analyse the effect of
those differences on photosynthesis.
F r o m actual data aswell asfrom calculated results it became evident that no
saturation of photosynthesis wasobtained at 225W m ~ 2 . F o r single leaves the
level ofirradiance saturation hasbeen determined at42W m " 2 (REINKEN et al.,
1973) andbetween 200and240W m " 2for coslettuce (SARTI, 1973). BROUWER
and HUYSKES (1968) andV A NHOLSTEIJN etal. (1977) didnotobserve saturation
levels for whole shoots at 209 resp. 154 W m - 2 .
Figure 1 shows that differences between the photosynthesis light response
curves depend on the basis of expression. O n weight basis the sequence ofthe
photosynthesis levels changes and some differences decrease as shown by
BROUWER a n d HUYSKES (1968). The small difference between calculated and
measured values ofR d andthelowstandard errors formost parameters indicate
that theuse of equations (3)and(5)onplant level gives reliable results. A C O C K et
al. (1976b, 1978) also obtained reliable results with other crops, for which they
used a crop model based on a similar leaf model.
Photochemical
efficiency
Although differences between gross (in1= 0)andnet(inI = I c ) photochemical efficiencies exist, theconclusions inthis paper based ona g arevaluable for<xn
as well, since thecorrelation between <xg-anda n -valueswas high (r = 0.99).The
high correlation betweena ga n dSandthe goodfit of the multilinear regressionof
a g with 4 plant characteristics justify the outlined theory about the application
of ocgto define a basis ofexpression forthephotosynthetic rates anda corrected
value for I c . The correlation coefficient of ocg with the 3 plant characteristics
decreased with increasing age,which might beascribed toahigher number of leaf
layers, themore complex structure of the older plant, andthesenescence of the
older leaves of the plant.
In older plants a relatively smaller part of the total leaf area intercepts light
and contributes t othe positive net photosynthesis than inyoung plants. The data
of the photochemical efficiencies on the basis of leaf area are therefore inaccurate, but they permit rough comparison with other data. The highest devalues areobserved inthegroup with theyounger plants andthelowest ones in
group C. These data aresimilar with those on leaf level ( L U D L O W and WILSON,
1971b; PEAT, 1970) and plant level ( N I L W I K , 1980a). Moreover, young lettuce
plants have a more open structure, which canresult in a higher photochemical
efficiency asshown by N I L W I K (1980a) for sweet pepper plants. Typical sunand
shade-effects o n a g oro^ asreported forsingleleavesbysome authors (BJÖRKMAN
and H O L M G R E N , 1966; BÖHNING and BURNSIDE, 1956; L O A C H , 1967; SARTI,
1973) arenot noticeable for alltreatments. In single leaves structural and morphological differences like leaf thickness, structural changes inchloroplastsand
chlorophyll content are responsible for these effects. Other authors (CHARLESE D W A R D S et al., 1974; L U D L O W and WILSON, 1971a)reported no influence of the
level of irradiance during cultivation ona g ora n . F o rsingle plant measurements
contrasting results arealso reported. N I L W I K (1980a) observed differences inal„
Meded. Landbouwhogeschool Wageningen 81-12 (1981)
13
mainly caused bythespatial structure ofthe sweet pepper plant asa result of
pretreatment a n dBROUWER a n dHUYSKES (1968) found different a n -valueson
soilcover basis fortwoapplied treatments, butidentical photochemical efficiencies onplant orcanopy level were observed byA C O C K etal. (1976a) and L o u WERSEand V A N DEZWEERDE(1977).The efficiencies calculated from plantd a t ain
these experiments with lettuce arelower than those from single lettuce leaves
(SARTI, 1973)or other leaves ( A C O C K et al., 1979)andthose calculated from
other plant orcanopy data which arecorrected fornumber of leaf layers ( A C O C K
et al., 1976a; N I L W I K , 1980a).
Dark respiration
The P m ofthephotosynthesis-irradiance responsecurvedepends onthe 'overallplant conductance' forC 0 2 (xg)andtheC 0 2 - c o n c e n t r a t i o n ,which isthe same
for allmeasurements inexperiment 1.The P m n depends also onthe estimated
dark respiration (R d ). These estimated R d -values perplant never exceeded 17%
of the P perplant but this percentage increased atvalues below P
LOGAN
(1970)found similar percentages forbirch trees over thewhole season.T h elower
percentage of theolder groups wasnotexpected forlettuce,sincethe plants of age
B andC possess more aged leaves a n da higher number of leaves excluded
from thelight source. D a r k respiration decreases with age ( L U D L O W and WILSON,
1971b) andthelower rates with increasing agefor lettuce canbea result o f t h a t
effect. M C C R E E a n d T R O U G H T O N(1966)a n d L U D W I Getal.(1965)concluded from
canopy data that therespiration ofthe lower andolder leaf layers wasextremely
low. F o r lettuce, however, the 'shade' leaves consist ofa mixture ofold leaves
and newly formed leaves within thehead ofthe plant.
Plant conductance for C02
The plant conductance forC 0 2 (x)determines toa great extent P m g( = x g C)
and P m n ( = x n C) inlight series. Thecarboxylation efficiency isincorporated in
this 'overall conductance for C 0 2 ' , which represents an average value for all
leaves of the plant. These values candiffer considerably as wasreported by
ACOCK etal. (1978) forleaves ina tomato canopy. A higher plant conductance
means a high carboxylation efficiency and/or alowresistance forthe transport
and diffusion ofC 0 2 from the external airtothecarboxylation sites.Onleaf level
the total resistance canbe divided in the boundary layer resistance (r a ), the
stomatal resistance (r s ) a n d the residual resistance (r m ) (BIERHUIZENand SLATYER,
1964; GAASTRA, 1959; L U D L O W a n d W I L S O N , 1971a). F o r lettuce-plants the r m ,
i.e. theresidual resistance, canbeconsidered asthemost important factor ( V A N
HOLSTEIJN et al., 1977), which isin agreement with data of BEARDSHELL et al.
(1973), FRASER a n d B I DWELL (1974), GAASTRA(1959,1962), a n d , at an irradiance
level below 50 W m ~ 2 , of N I L W I K and T E N BÖHMER (1981).
On plant andcanopy levelthe transport processismore complicated and other
C 0 2 sources outside the leaf occur. Another resistance, r a cr , the plant or crop
resistance determining thetransport ofC 0 2 from theatmosphere tothe leaves,
can play a more significant role (GAASTRA, 1966). This r a cr isconsidered to be
14
Meded. Landbouwhogeschool Wageningen81-12 (1981)
lowfor most crops,but for lettuceplants which have a more dense leaf package
thisresistancecanbemoreimportant. VAN HOLSTEIJNetal.(1977)paid no attentiontotheroleofra crintheirexperiments,sincetheyusedaconstantvalueonleaf
basisfor raandcalculated rs-and rm-valuesonbasisoftheleafareaofallleavesof
the plant. The level of irradiance below saturation and the calculation methods
of rm according to GAASTRA (1959) also contributed to an overestimation of rm
(and rs)by VAN HOLSTEIJN et al. (1977). JONESand MANSFIELD (1970) measured
detached leaves oflettuceand they observed values of the total resistance above
30scm"', but the applied levelofirradiance (14.4Wm~2) wasbelow saturation
for lettuce leaves. The average total conductance on leaf basis (from P^ g)
decreases with age, which can be caused by the more complex structure of the
plant, by more self shading, as found by ACOCK et al. (1978) with canopy data,
and slightlybythe increaseofmesophyll and stomatal resistances (LUDLOW and
WILSON, 1971b). A decrease in conductance for C 0 2 means an increase in total
resistance for the transport of C 0 2 .
The higher conductance at 26° compared to 14°C indicates that for these
photosynthesis measurements the optimum T-value is found above 14° and
probably near 26°C,asobserved by NILWIK (1980b)for sweetpepper,where the
optimum value inmost situations wasobtained at 24°C. For long term growth,
however,alower temperature seemstobefavourable for ahighconductance for
C 0 2 transfer. Adistinctionbetween thetemperatureeffect ofgrowth and thegas
exchange measurement ismore difficult todraw inTable 5,due to the restricted
number of conductance data. Only a slight influence of the environmental
factors in these experiments on rs is expected (JONES and MANSFIELD, 1970).
Different x-valuestherefore arealsocausedbyplant structure,moreselfshading,
theinfluence ofracr and theroleofinternal factors affecting rm.AUGUSTINEetal.
(1976), for instance, concluded that differences in carboxylation efficiencies
between genotypes were determined by anatomical and biochemical factors,
which are expressed in rm and BJÖRKMAN (1968) observed differences in carboxydismutase activity of several species grown in strong and weak light.
Specific leaf weight and photosynthesis
Theleafarea ratio (LAR) and the specific leafweight (SLW),calculated from
plantdata,areconsidered aslessreliableestimatesfor amorphological characteristiclikeleafthickness (VAN HOLSTEIJN, 1980b),butcan beusedasindicators for
some morphological properties. Only small differences between SLW-values of
ages A, Band C were observed for treatment I, II, III and IV. The differences
betweenthevaluesofthe4treatments weresignificant. Temperature and levelof
irradiance during cultivation both affect leaf thickness. The influence of leaf
thickness on Pm gintheseexperiments isnot alwayssimilar, sincethe correlation
coefficient (r)between SLW and P m>n .a-' at 14°is0.73and at 26°C itis0.55.In
other experiments with single plants or canopies usually a higher positive relation between SLW and the maximal photosynthetic rates is observed (LouWERSEand VAN DEZWEERDE, 1977; NILWIK, 1980b).Thecorrelation coefficients
(r)between xn'and SLW for plants measured at 14°and 26°C are 0.57 and 0.63,
Meded. Landbouwhogeschool Wageningen81-12 (1981)
15
respectively. These coefficients may have been negatively influenced bythe ages
of the plants inexperiment 1,since plants of the 3age groups gave almost similar
SLW-values but different plant conductances for C 0 2 .
The analysis of variance of net photosynthetic rates on the basis of ocg of
irradiance level of 35and 100W m " 2 shows no significant differences between
group Ba n dC.Theabsence of any significant differences between the corrected
P n 3 5 -values of the 4 treatments suggests a similar assimilation of the 'sun' and
'shade' plants atthat level of irradiance, which isincontrast tosome other results
obtained from plant or canopy measurements a n dexpressed on leaf unit basis
( B R O U W E R and HUYSKES, 1968; L O G A N and K R O T K O V , 1968; LOUWERSE and
VAN DEZWEERDE, 1977;PATTERSON et al., 1977). Their observed differences
between sun and shade plants aredue tothe various structures and morphologies
of the plants and the leaves and the applied basis of expression for the photosynthetic rates, andnotto fundamental differences inphotosynthetic processes.
The spatial structure of the lettuce plant compensates forthedifferences in leaf
structure and morphology at that level of irradiance.
Light compensation point
The influence of measurement temperature islarger than theeffects of treatment andageon I c . Lettuce plants seem to adapt well to theapplied irradiance
levels inthis experiment. The level of irradiance inthewinter season approaches
the light compensation point. Ageandplant structure affect thelight interception andself shading andthus I c . Moreover, young plants have a relatively high
number ofjust unfolded leaves,a n dthis results inhigher I c -values ( L U D L O W a n d
WILSON, 1971b). Observed light compensation points areaverages of the compensation points of all leaves of theplant. Reported values of single leaves are
lower than thevalues in this experiment (DULLFORCE, 1971; HEATH and M E I D NER, 1967). Themaintenance ofa lowtemperature seems to beessential at poor
light conditions in order to obtain a lowrespiratory rate anda lowI c , since an
increase of 1°Cincreases I c with one W m _ 2 , a slightly lower value than found by
N I L W I K (1980a) with sweet pepper plants.
Photosynthesis and C02 compensation
concentration
T h e maximal P n -valuesof theC0 2 -seriesaremainly determined by differences
in theestimated photochemical efficiencies (from: P m n = ocnI).TheP n -valuesof
treatment I and III, measured at 142W m " 2 ,are influenced by temperature
during cultivation a n d during the gas exchange measurement (LOACH, 1967;
N I L W I K , 1980b). Calculation of P m n onthebasis of data over arange between 80
and 1400m g C 0 2 m " 3 (in experiment 2) can give misleading results, since a
higher C0 2 -concentration can cause an increase in the stomatal resistance for
lettuce (JONES a n d MANSFIELD, 1970) and residual resistance ( N I L W I K and T E N
BÖHMER, 1981; W I T T W E R and R O B , 1964).
The calculated values ofC c arein agreement with theobserved data. TheC c values, which provide an average estimate of the C0 2 -concentration in the
intercellular spaces for the whole plant, are slightly higher than the values
16
Meded. Landbouwhogeschool Wageningen81-12 (1981)
reported by HEATH and MEIDNER (1967) for detached leaves at comparable
temperatures. BRAVDO (1971) also observed higher C 0 2 compensation concentrationsofleavesandstemtogetherascomparedwithconcentrationsofsingle
leaves.TheleaveswhichinterceptdirectlighthavelowerCc-valuesthantheyoung
and old 'shade'leaves (NILWIK, 1980b).Theshadepart oftheplant and the stem
contributemoretoR d(BRAVDO, 1971)andformanextraC 0 2 source,althoughthe
contribution of the stem for lettuceislow and also R d has a low value.A higher
temperature during themeasurements causesahigher Cc (HEATH and MEIDNER,
1967; NILWIK, 1980b),duetoanincreaseinphotorespiration intheleaveswhich
intercept irradiance and to a higher R d of the other plant parts. A significant
influence of the treatment temperature on Cc is not expected (NILWIK, 1980b).
Withtheuseoftheeffective leafarea(EL)forananalysisofthe photosynthesis
data the interpretation of the results is still complex. More extensive studies of
the morphology of a lettuce plant are essential to solve the problems of light
interception, C 0 2 transport and diffusion from the external air to the carboxylation sites. The 'ideal' plant seems to be a plant with an open structure, a low
racr,without ahead andwithagood lightinterception ofalltheleaves,but at the
moment such a plant shape is not of commercial interest.
SUMMARY
In twoexperiments photosynthesis ofwholelettuce shoots wasmeasured ina
closed system. During cultivation in both experiments 4treatments of different
irradiances and temperatures were applied to obtain plants with different habitus. In experiment 1 the response of photosynthesis to irradiance (I) was
measured for plants of 3ages at 14°and 26°C. In experiment 2the response of
photosynthesis to C0 2 -concentration (C) was measured at 15° and 25°C.
Attention was paid to the basis of expression for the photosynthetic rates,
obtained per plant. The basis,effective leaf area (EL), isequal to soilcover (S),
leaf area (A)and leafweight (W)and to thegross photochemical efficiency (ag),
since EL = oig.a~Jon withagcon as the constant value ofocgwhen alllight quanta
are absorbed. A multilinear regression model of ocgwith S, A and W gave high
correlation coefficients, while addition of the profile area did not improve the
model significantly.
Inexperiment 1 thegross photochemical efficiency per plant (ag)and per unit
leafarea(ocg),themaximalgrossand netphotosynthesis (Pm gand P m n )per plant
andperunitleafarea(P,!,^),thedarkrespiration (R d )perunitleafweightand the
light compensation point (Ic) were calculated by curve-fitting. In a 3-way analysis of variance some of these parameters, the net photosynthetic rates onocgbasis at 35 and 100 Wm~ 2 and at light saturation, I c and the corrected I c (=
Ic.ocg)wereanalysed.Thevaluesofocgand P^gdecreased withincreasing age.The
ag-value was not affected by treatment and measurement temperatures. The
photosynthetic rates on ag-basisgave only lower values for the group of young
plants. The effect of treatment on P n diminished at 35Wm~ 2 , but increased at
Meded. Landbouwhogeschool Wageningen81-12 (1981)
17
100Wm" 2 and became more distinct at the saturated level of irradiance. The
corrected P n at 35 Wm" 2 is higher at 14° than at 26°C. This difference disappeared at 100Wm" 2 and at saturating ItheP m nwashigher at 26°than at 14°C.
Ic isstrongly influenced bymeasurement temperature. Corrected Ic-valueswere
affected by age and not by treatment.
In experiment 2the net conductance for C 0 2 per plant (xn)and per unit leaf
area (z\), the P m nand P^ n,and the C 0 2 compensation concentration (Cc) were
calculated. An increase in measurement temperature decreased Tn and x*, but
affected the maximum photosynthetic rates positively. C c depends strongly on
temperature during measurement.
Observed differences between theparameters arediscussed, alsoinrelation to
the stomatal and residual resistances and morphological properties of the plant
such as specific leaf weight and plant structure.
ACKNOWLEDGEMENTS
I wish to thank Prof. Dr. Ir. J. F. BIERHUIZEN for reading and critisizing the
manuscript. I am much indebted to Drs. H. J. M. NILWIK for the inspiring
discussions and for his assistance in solving the mathematical problems. I also
wish to thank Mrs. BERNADET TER HORST for her assistance in experiment 1.
Acknowledgement is due to Mr. H. VAN LENT for his preparation of Figure 1.
18
Meded.Landbouwhogeschool Wageningen81-12 (1981)
REFERENCES
ACOCK, B.,CHARLES-EDWARDS,D.A., FITTER,D.J., HAND,D.W., LUDWIG, L.J., WARREN WILSON,
J. andWITHERS, A. C.:The contribution ofleavesfrom different levelswithinatomato cropto
canopy net photosynthesis. Anexperimental examination oftwo canopy models.- J. exp. Bot.
29: 815-827, 1978.
ACOCK, B., CHARLES-EDWARDS, D.A.and HAND,D.W.:Ananalysisofsomeeffects ofhumidity on
photosynthesis byatomato crop under winter light conditions andarange ofcarbon dioxide
concentrations. - J. exp. Bot. 27: 933-941, 1976a.
ACOCK, B.,CHARLES-EDWARDS, D.A.andSAWYER, S.:Growth response ofachrysanthemum crop
to theenvironment. III.Effects ofradiation and temperature ondrymatter partitioningand
- photosynthesis. - Ann. Bot. 44: 289-300, 1979.
ACOCK, B.andHAND, D.W.: The effect ofday temperature andC 0 2 concentration on net
photosynthesis. - Ann. Rep. G.C.R.I., Littlehampton :49,1974.
ACOCK, B.,HAND,D.W., THORNLEY, J. H. M.and WARREN WILSON,J. :Photosynthesis instands of
green pepper forapplication ofempirical and mechanistic models to controlled-environment
data. - Ann. Bot. 40: 1293-1307, 1976b.
AKITA, S., MURATA, Y.and MIYASAKA, A.:Onlight-photosynthesis curves ofrice leaves.- Proc.
Crop Sei. Soc. Jap. 37:680-684, 1968.
ALBERDA, TH.etal.:Crop photosynthesis: methods andcompilation ofdata obtained with mobile
field equipment. - Agr. Res. Rep. 865,CABO, Wageningen: 1-46,1977.
AUGUSTINE, J. J., STEVENS, M. A., BREIDENBACH, R. W. and PAIGE, D. F.:Genotypic variation in
carboxylation of tomatoes. - Plant Physiol. 57:325-333, 1976.
BEARDSELL, M.F., MITCHELL, K.J.and THOMAS, R. G.: Effects ofwaterstress under contrasting
environmental conditions ontranspiration andphotosynthesis insoybean. - J. exp.Bot. 24:
579-586, 1973.
BENSINK, J.: On morphogenesis oflettuce leaves inrelation tolight and temperature. - Meded.
Landbouwhogeschool, Wageningen 71(15): 1-93, 1971.
BIERHUIZEN, J. F.andSLATYER, R. O.: Photosynthesis ofcotton leaves under a range of environmental conditions inrelation tointernal andexternal diffusive resistances.- Aust. J.biol.
Sei. 17:348-359, 1964.
BJÖRKMAN, O.: Carboxydismutase activity inshade-adapted and sun-adapted species of higher
plants. - Physiol. Plant. 21: 1-10, 1968.
BJÖRKMAN, O. andHOLMGREN, P.: Photosynthetic adaptation to light intensity inplants nativeto
shaded andexposed habitats. - Physiol. Plant. 19:854-859, 1966.
BÖHNING,R.H.and BURNSIDE,C.A.:Theeffect oflightintensityonrateofapparent photosynthesis
in leaves of sun andshade plants. - Am. J. Bot. 43: 557-561, 1956.
BRAVDO, B.A.:Carbondioxide compensation points ofleaves andstems andtheir relation to net
photosynthesis. - Plant Physiol. 48:607-612, 1971.
BROUWER, R.andHUYSKES, J.A. :Aphysiological analysis ofthe responses ofthe lettuce variety
'Rapide' and itshybrid with 'Hamadan' today-length and light intensity. - Euphytica17:
245-251, 1968.
CARMER, S.G. and SWANSON, M. R.:An evaluation ofthepairwisemultiplecomparison procedures
by Monte Carlo methods. - J. Amer. Statist. Assoc. 63: 66-74, 1973.
CHARLES-EDWARDS, D.A.and ACOCK, B.: Growth response ofa chrysanthemum crop to the
environment. II. Amathematical analysis relating photosynthesis andgrowth.- Ann. Bot. 41:
49-58, 1977.
CHARLES-EDWARDS,D. A., CHARLES-EDWARDS,J.and SANT,F. I.:Leafphotosyntheticactivityinsix
temperategrassvarietiesgrown incontrastinglightand temperatureenvironments.- J. exp.Bot.
25: 715-724, 1974.
CHARLES-EDWARDS, D.A.and LUDWIG, L.J.: Amodelforleafphotosynthesis byC 3 species.- Ann.
Bot. 38: 921-930, 1974.
Meded. Landbouwhogeschool Wageningen81-12 (1981)
19
DULLFORCE, W.M.:Effects oflight, temperature andcarbon dioxide onthegrowth of glasshouse
lettuce (Lactuca sativa L.). - Ph.D.Thesis, Un. Nottingham: 1-150,1968.
DULLFORCE, W.M.:Thegrowth ofwinter glasshouse lettuce with artificial light.- Acta Hort.22:
199-210, 1971.
DUNCAN, W. G., LOOMS, R. S., WILLIAMS, W. A. and HANAU, R. :A model for simulating photo-
synthesis in plant communities. - Hilgardia 38: 181-205, 1967.
EENINK,A.H.:Energiebesparing indeslateelt door veredeling.- Landb. Tijdschrift 90:483-487,
1978.
EENINK, A.H.and SMEETS, L.: Genotype x environment interactions with lettuce (Lactuca L.) in
relation tothedevelopment of genotypes forgrowing under poor energy conditions.- Neth.J.
agric. Sei. 26: 81-98, 1978.
ENOCH, H.Z.andSACKS,J. M.:An empirical model ofC 0 2 exchange ofaC 3 plant inrelation to
light, C0 2 -concentration and temperature. - Photosynthetica 12: 150-157, 1978.
FRASER,D.E.andBIDWELL,R.G.S. :Photosynthesis and photorespiration during theontogenyof
the bean plant. - Can. J. Bot. 52: 2561-2570, 1974.
GAASTRA,P.:Photosynthesis ofcropplantsasinfluenced bylight,carbon dioxide,temperature, and
stomataldiffusion resistance.- Meded. Landbouwhogeschool, Wageningen59(13): 1-68,1959.
GAASTRA, P.: Photosynthesis of leaves of field crops. - Neth. J. agric. Sei. 10: 311-324,
1962.
GAASTRA,P.:Somephysiological aspects ofC0 2 -application inglasshouse culture.- Acta Hort.4:
111-116, 1966.
HEATH, O.V.S.and MEIDNER, H.:Compensation points and carbondioxide enrichment forlettuce
grown under glass in winter. - J. exp. Bot. 18: 746-751, 1967.
HOLSTEIJN,H.M.C. VAN:Aclosedsystemfor measurementsofphotosynthesis,respiration and C 0 2
compensation points. - Meded. Landbouwhogeschool, Wageningen 79 (10): 1-14,1979.
HOLSTEIJN,H. M.C.VAN: Growth oflettuce.I.Covering ofsoil surface. - Meded. Landbouwhogeschool, Wageningen 80(7): 1-27,1980a.
HOLSTEIJN,H.M.C.VAN: Growth oflettuce. II.Quantitative analysis ofgrowth. - Meded. Landbouwhogeschool, Wageningen 80 (13): 1-24,1980b.
HOLSTEIJN, H. M.C. VAN, BEHBOUDIAN, M. H. and BONGERS, H. C. M.L.:Water relationsoflettuce.
II. Effects ofdrought ongasexchange properties oftwo cultivars. - Scientia Hort. 7: 19-26,
1977.
JONES,R.J.and MANSFIELD, T.A.: Increasesinthediffusion resistance ofleavesinacarbon dioxide
enriched atmosphere. - J. exp. Bot. 2 1 : 951-958, 1970.
KOLLER, H. R. and DILLEY, R. A.: Light intensity during leaf growth affects chlorophyll concentration and C 0 2 assimilation ofsoybean chlorophyll mutant.- Crop Sei. 14:779-782,1974.
LOACH, K.:Shadetoleranceintreeseedlings.I.Leafphotosynthesis andrespiration inplants raised
under artificial shade. - New Phytol. 66: 607-621, 1967.
LOGAN, K.T.: Adaptations ofthe photosynthetic apparatus ofsun andshade grown yellow birch
(Betula alleghaniensis Britt.). - Can. J. Bot. 48: 1681-1688, 1970.
LOGAN,K.T.and KROTKOV,G. :Adaptationsofthephotosyntheticmechanismofsugarmaple (Acer
saccharum) seedlings grown in various light intensities. - Physiol. Plant. 22: 104-116,1968.
LORENZ, H. P. and WIEBE, H. J.: Effect of temperature on photosynthesis of lettuce adapted to.
different light and temperature conditions. - Scientia Hort. 13: 115-123, 1980.
LOUWERSE, W. and VAN OORSCHOT, J. L. P.: An assembly for routine measurements of photosynthesis, respiration andtranspiration ofintact plants under controlled conditions. - Photosynthetica 3 : 305-315, 1969.
LOUWERSE, W.andVANDEZWEERDE, W.:Photosynthesis, transpiration andleaf morphology of
Phaseolus vulgaris and Zea mays grown at different irradiances in artificial and sun light.
- Photosynthetica 11:11-21,1977.
LUDLOW, M. M. and WILSON,G. L.: Photosynthesisoftropical pasture plants.II.Temperature and
illuminance history. - Aust. J. biol. Sei. 24: 1065-1076, 1971a.
LUDLOW, M. M. and WILSON,G.L.: Photosynthesis oftropicalpastureplants.III. Leafage.- Aust.
J. biol. Sei. 24: 1077-1087, 1971b.
LUDWIG,L.J.,SAEKI,T.and EVANS,L.T.: Photosynthesis inartificial communities ofcotton plants
20
Meded. Landbouwhogeschool Wageningen81-12 (1981)
in relation to leaf area.I.Experiments with progressive defoliation of mature plants.- Aust.J.
biol. Sei. 18:1103-1118, 1965.
MARSHALL, B. and BISCOE, P.V.: Amodel describing the dependence ofnet photosynthesison
irradiance. I. Derivation. - J. exp. Bot. 31: 29-39, 1980.
MCCREE, K.J. and TROUGHTON, J. H.: Non-existance ofan optimum leaf area index for the
production rateofwhitecloverunderconstantconditions.- Plant Physiol.41:1615-1622,1966.
NILWIK, H.J. M.: Photosynthesis ofwhole sweet pepper plants. I. Response toirradiance and
temperature asinfluenced bycultivation conditions. - Photosynthetica 14: 373-381, 1980a.
NILWIK, H. J.M. : Photosynthesis ofwhole sweet pepper plants. II. Response tocarbon dioxide
concentration, irradiance and temperature asinfluenced by cultivation conditions. - Photosynthetica 14:382-391, 1980b.
NILWIK, H. J. M.and TEN BÖHMER, H. :An improved closed systemfor continuous measurement of
photosynthesis,respiration and transpiration.- Meded. Landbouwhogeschool, Wageningen 81
(4): 1-9, 1981.
PATTERSON, D. T., BUNCE, J. A., ALBERTE, R. S. and VAN VOLKENBURGH, E.: Photosynthesis in
relation toleafcharacteristics ofcotton from controlled and field environments.- Plant Physiol.
59: 384-387, 1077.
PEAT,W.E.:Relationships betweenphotosynthesisandlightintensityinthetomato.-Ann. Bot.34:
319-328, 1970.
RABINOWITCH, E.I.: Photosynthesis and related processes. Vol. II. Interscience Publ. Inc., New
York, 1951.
REINKEN, G., WEISS, B. and ZISCHKA, W.: Die Photosynthese der wichtigsten Gemüsearten unter
Glass. - Ber. Versuchen Untersuchungen II: 45-67, 1973.
SALE, P.J.:Net carbon exchange ratesoffield-growncrops in relation to irradiance and dry weight
accumulation. - Aust. J. Plant Physiol. 4: 555-569, 1977.
SARTI,A.:Growth and photosynthetic activity oïLactuca sativacv.romana,cultivated inthree day
light intensities.- Lab. Radiobiochimica ed Ecofisiologia Vegetali.C.N.R., Roma: 1-13,1973.
SARTI,A., LOUASON, G. and CORNIC, G.:A study of the Kok-effect on Lactuca sativa cv romana.
- Phytotronic Newsletter 16: 38-43, 1977.
SORIBE,F.I.and CURRY, R.D. :Simulationoflettucegrowth inanair-supported plastic greenhouse.
- J. agric. Engin. Res. 18:133-140, 1973.
TAKAKURA, T.:Plant growth optimisation usingasmallcomputer.-Acta Hort. 46: 147-156,1975.
TATSUMI, M. and HORI, Y.: Studies on the photosynthesis of vegetable crops.I.Photosynthesis of
young plants ofvegetables inrelation tolight intensity. - Bull. Hort. Res. Stat. Hiratsuka,
Kanagawa, Ser.A8: 127-140, 1969. (Eng. summary and subtitles.)
TATSUMI, M. and HORI, Y.: Studies on photosynthesis of vegetable crops.II. Effect of temperature
on the photosynthesis of young plants of vegetables in relation to light intensity.- Bull. Hort.
Res. Stat. Hiratsuka, Kanagawa, SerA9: 181-188, 1970 (Engl, summary andsubtitles).
THORNLEY, J. H. M. :Photosynthesis. In:Mathematical ModelsinPlant Physiology. A quantitative
approach to problems in plant and crop physiology. Academic Press, London:92-110, 1976.
TOOMING, H. : Mathematical model of plant photosynthesis considering adaptation. - Photosynthetica 1: 233-240, 1967.
WIEBE,H.J.und LORENTZ,H.P.:WirkungvonWechseltemperatur undlichtabhängiger Temperaturregelung auf des Wachtums vonKopfsalat. - Gartenbauwiss. 42:42-45, 1977.
WITTWER, S.H.and ROB,W. :Carbon dioxideenrichment ofgreenhouse atmospheres for food crop
production. - Econ. Bot.18:34-56, 1964.
Meded. Landbouwhogeschool Wageningen81-12 (1981)
21