Effects Temperature Photosynthesis CO2 Evolution in Light ...

Plant Physiol. (1969) 44, 671-677

Effects of Temperature on Photosynthesis and CO2 Evolution in Light and Darkness by Green Leaves1

Choy-Sin Hew2, G. Krotkov3, and David T. Canvin

Department of Biology, Queen's University, Kingston, Ontario

Received 'November 4, 1968.

Abstract. Using an open and a closed system of gas analysis, it was found that CO., evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant,

and jackbean) have a different response to temperature. While the rate of CO, evolution in light increased with incre-asing temperature from 17 to 350 and then declined, the rate of CO, evolution in darkness increased continuously up to 400. The rate of CO, evolution in light was affected by light intensity. At 1800 ft-c and below 350 the rate of CO2 evolution in light was greater than in darkness, but above 350 it beoame lower than in darkness. The

Q10 for CO2 evolution in light was consistently lower than that in darkness.

Apparent photosynthesis decreased with increasing temperature, from 20 to 400 and its rate was affected 'by both light intensity and oxygen concentration. In leaves of dicotyledonous plants studied 'the decrease in apparent photosynthesis between 20 to 300 at 21 % 02 was shown to be due primarily to an increase in CO. evolution in light with relatively little effect on photosynthesis.

In corn which does not evolve CO2 during illumination there was little effect of increasing

temperature on the rate of apparent photosynthesis.

The different response to temperature of CO., evolution in light and in darkness support

the earlier conclusion that these are 2 different processes.

It has been reported that the rates of CO2 evolution by green leaves in light are affected by both O, concentration (6, 9, 11, 14, 29) and light intensity (3, 6, 15, 17, 18, 27). Decker (3) has shown that the post-illumination CO., outburst from tobacco at 33.5' was 3 times as large as that at 17.50 and Zelitch (34) has also shown that CO., evolution in light increases with a temperature increase from 250 to 350. Further data on the effect of temperature on CO. evolutioni in light is scanity although the response of CO.2 evolution in darkness has been well documented (19). Additional knowledge would be of interest since there is increasing evidence to in.dicate that in green 'leaves the processes leading to the evolution of CO., in light and in darkness mav

be different (6, 9, 11, 17, 23). The present investi-

gation describes the results obtained from a study of the effects of temperature on photosynthesis and CO., evolution in light and in darkn-ess by green leaves.

Materials and Methods

Suinflow%,er (Helianthius annaulixs L. 'Ml1ennonite') and corn (Zea nays L.) w,ere grown as described

Supported by the National Research Council of

Canada. 2 Present address: Department of Biology, Brandeis

University, Waltham, Massachusetts 02154. 3 Deceased January 29, 1968,

previously '(15). Soybean (Glycine max Merr.)

jackbean (Canavalia ensiformis D. C.) watermelon (Citrullus vulgaris Schard.) and eggplant ((Solanum inielanigena L.) were grown in the greenhouse during the summer of 1966. Fully ex'panded leaves from 20-dav old soy-bean and jackbean plants and 30 to 35-day old watermelon and eggplants were used.

The closed and the open systems of gas analysis

were the same as described previously ( 15, 16). The closed system was used to study the magnitude of the post-illumination CO. outburst, the CO., com-

pen'sation point, and the effect of CO) concen,tration

on -the rate of apparent photosynthesis at various

temperattures. The open system. was used to studv the effect of temperature on the steadv rates of apparent photosynthesis at 0.03 % CO2 in air anid CO., evolution into CO-free air in light and in

darkness.

The various leaf temperatures were obtained by circulating water (Hakke temperature controller) of the desired temperature around the leaf chamber. I,eaf temperature was maintained within ?+O.5' of

the desired temperature as measured by a copperconstanitan thermocouple pressed to the underside of the leaf. Leaf temperature could be changed ?+50 in 10 to 15 min.

Light intensity was 1800 ft-c and the flow-rate

of air 2 liters per min.

For dicotyledonjous leaves, leaf chambers similar

to those described previouslv were used (15). The leaf chamber for corn consisted of 2 similar 'Plexiglas' sheets with the ediges of the faces lined with

sponge rubber. The 2 halves were clamped over

671

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672

PLANT PHYSIOLOGY

a leaf to enclose a segment of the leaf in the leaf chamber. The sponge rubber allowed an air tight seal on the leaf surface without damage to the leaf.

160 1

Sb.%

'CY: N 140

.C

I -)

c 120

%-)q

N

1001I

0

ua a cm

801

cq 0a

30

ic a

60

t.1~~~~~~ ;

'

I

Results

Effects of Temperature ont Photosynthesis, CO0 Evolution in Light and in Darkness by a Single, Attached Suitflozwer Leaf. The rate of apparent photosynthesis of a suniflower leaf decreased as the temperature increased (Fig. 1). The rate of 'true' photosynthesis calculated from the summation of the rates of apparent photosynthesis and CO., evolution in light, also decreased with increasing temperatures. The rate of CO., evolution in darkness increased wvith increasing temperature up to 400 whereas the rate of CO., evolution in light increased with increasing temperature to 350 and then declined. The rate of CO., evolution in light was higher tlhain the

rate of CO., evolutioin in darkness at tenmperattures below, 350 but at higher temperatures it became

lower than that in darkness. Further analysis of the data shown in Fig. I is

presented in tables I and II. The Qlo for both

'true' and apparent photosynthesis was below one at both temperature raniges, with a somewhat higher Q1, for 'true' than for apparent photosynthesis (table I). The Q,, of 09.2 between 20 anid 300, inidicated

Table T. The Tempteralture Coefficient (Q,,u) of Ap-

parent Photosynthesis, 'Truie' Photosynthesis, CO2

Evolution in Light and in Darkness of Attached Sunflower Leaves as Measutred

in an Open Systemii ILight intensity was 1800 ft-c and the gas phase was 21 % O.,.

Temperature coefficient

4cL

200 to 300 302 to 400

N3

Oj

40

20

Ul

QIO

'True' photosynthesis'

0.92

0.73

Appareint photosynthesis

0.82

0.60

CO., evolution in light

1.45

1.08

Co., evolutioin in darkiness

1.75

1.57

1 Apparent photosynithesis + CO., evolutionI in light.

7,

15 20 25 30 35 40 ?C

Te mper a t u re

,-v Tr ue Photos ynthesi s +- t Apparent Photosyn thesis

C02 Evol ution in LIark nes C 02 Ev ol jlion i n Li ght

FIG. 1. Effect of temperature on the rates of 'true' photosynthesis, apparent photosynthesis, CO,, evolution in light and in darkness of attached sunflower leaves, as measured in an open system. Light intensity was 1800 ft-c and the gas phase was 21 % O0. Vertical bars indicate S.D. of 3 leaves.

Table II. Effect of Temnperaturc on the Relative Rates of A4pparent aind 'True' Photosynthesis of Attached Sunflowuer Leaves

Light inteInsity was 1800 ft-c anid thle gas phase was 21 % 02.

Temperature

Apparent 'True' 'True' Photo- photo- photosynthesis synthesis1 synthesis2

deg

%

%

%

)0

1008

10(

100

25

92

97

98

30

82

93

95

35

68

80

90

40

50

67 .80

1 Apparent photosynthesis + CO, evolution in iight.

2 Apparent photosynthesis + CO. evolution in darkness.

3 Percentage of rate at 200.

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HEW ET AL.-EFFECT OF TEMPERATURE ON PHOTOSYNTHESIS AND CO., EVOLUTION OF LEAVES 673

Table III. Effect of Oxygen on the Rate of Apparent Photosynthesis of Attached Sunflower Leaves at Different Temnperatures

Light intensity was 1800 ft-c.

Temperature

1 ?029 Apparent photosynthesis

deg

,ug COs,

hr-1 c1n-2 %

20

189 ? 2.01 100

30

180 + 2.5 95

40

131 ? 2.0 70

Mean + S.D. of 3 leaves.

21% O., Apparent photosynthesis

1ttg CO,

hr-l cnri2 % 135 + 1.7' 100 108 2.0 80 66 2.0 49

that the rate of 'true' photosynthesis within this

temperature range was fairly constant. The rate of CO. evolution in the light did not increase with temperature as rapidly as dark respiration and there was liftle increase between 30 to 400. When 'true' photosynthesis was calculated as the suum of apparent photosynthesis plus CO, evolution in light, the rate at 300 was 93 % of that at 200 and 67 % of that at 40' (table II). The decrease was slower when the rate oif 'true' photosynthesis was calculated by the summation of the rates of apparent photosynthesis plus CO2 evolution in darkness. Such a rate at 300

was still 95 % of that at 200 and at 400 it was &O %. The rate of apparent photosynthesis, on the other

hand, decreased quite rapidly with increasing tem-

perature. At 300 it was only 82 % of that at 20? and at 400 it was only 50 %.

This decrease in rate of apparent photosynthesis with increasing temperature was affected by oxygen concentration (table III). It was more rapid at 21 % 02. than at 1 % 0.2. Moreover, the rate of

apparen.t photosynthesis at 1 % 0., was fairly constant between 20 and 300.

The decline in the rates of apparent photosynthesis of sunflower leaves with inereasing temperature was apparent at both light intensities (Fig. 2). The decline appeared to be more pronounced at 1800

than at 300 ft-c but at 300 ft-c the rate of apparen.t photosynthesis at 370 was 25 % of that at 26? and the comparable value at 1800 ft-c was 60 %. At 170 the rates of CO., evolution at 300 ft-c and 1800 ft-c

were 24 and 27 ,ug CO., hr-1 em-2 respectively, but at 350 the respective rates were 30 and 44. In other

words, with an increase in temperature from 17 to

350 there was a faster rate of increase for the rate of CO} evolution in light at 1800 ft-c than that at 300 ft-c. Between 35 and 400 in light there was

only a slight increase in the rate of CO} evolution in light at both light intensities although the ra.te of

CO2 evolution in darkness increased progressively with increasing temperature up to 400.

The rate of apparent photosynthesis of a sun-

flower leaf in a closed system increase.d with in-

creased CO, concentration but for the same CO., concentration there was a proportional decrease in

the rate of apparent photosynthesis with temperature increases from 19 to 340 (Fig. 3). Carboxylation efficiency (i.e. the slope of the graph) was not significantly affected between 19 and 340 but a decrease was observed at 390 indicating a decrease in efficiency of photosyn,thesis. Similar observations have been reported previously by Decker (4). It

can also be seen that in a sunflower leaf the CO2

ilO ,

100

A

90

N 80

'E 770

190C 25 C

34*C

130

70.

120

60

c Cy 100 - 90

o0 80

r 70

c

60

50

40

c 50

40-

c 30

=

I--

-,, 1800 Ft-c

t-- 300 Ft - c

cI

50/ h~~~

40-

30

300 Ft-c

x 30-

20~~~~ ~~ 2 ~0 ~~~~

O

\

10 ;'

O

IS 20 25 30 35 40

I5 20 25 30 35 40 45

Tem De rct u re 'C

T e mpo ralsr *C

FIG. 2. Effect of temperature and light intensity on

the rates of apparent photosynthesis and CO, evolution

in light and in darkness of attached sunflower leaves as measured in an open system. Vertical bars-S.D. of 3 leaves.

- 60

0 39NC

50

50

Q40

30

4L 20

I0

N E 10

20

/ '~~50

/'

,,

/100 150

2 00 2 50

o 30'

o

40 "'

50r

FIG. 3. Effect of temperature on the rate of photo-

synthesis of attached sunflover leaves at various CO,

concentrations, as measured in a closed system. Light

intensity was 1800 ft-c and the gas phase was 21 % O0.

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674

PLANT PHYSIOLOGY

compensation point increased with increasing tem-

perature. The magnitude of the CO., outburst in darkness

immediately after illumination was also affected by temperature (Fig. 4). It increased with increasing

tempera.ture till about 300 and then declined. Effect of Temperature on Photosynthesis and

CO, Evolution in Light and Darkness by Attached

Leaves of Several Dicotyledonous Plants. In all the

other species studied, the rates of both apparent and 'true' photosynthesis were fairly constant between 20 to 250 and then decreased with increasing temperature,, (table IV). The rate of CO., evolution in light was higher thani in darkness at temperatures below 350, but lower than that in darkness above 35?.

Temperature coefficientts (Q,0) for the rate of

CO2 evolu.tion in light between 20 to 300 and 30 to 400 in all plant species examined varied between 1.4 and 1.5 and 0.97 and 1.17 respectively. The

temperature coefficient ((Q1o) for the rate of CO.,

evolution in darkness in the sanme temperature intervals was between 1.8 to 2.2 alnd 1.52 to 1.60 re-

spectively.

The effect o,f temnperattur-e oIn the CO., comllpenisation point, CO, outburst in darkness and car-

boxylation efficienc\y of these several plant species

wvas similar to those described for the sunflower leaf (16).

Effect of Temperature on Photosynthesis and CO. Evoluttion in Darkness by Attached Corn Leaves.

The rates of apparent photosynthesis and CO2 evolu-

tion in darkness and in ligh.t were determined for

attached leaves of corn in an open system (table Vr)*

At 1800 ft-c, the rate of apparent photosynthesis of

corn was identical over a temperature range of 20

Table V. Effec-t of Temitper(tutre on the Rates of Apparent Photosynthesis aitd ("O., Evolution in !)arkness of Attached Cornl Leaves, as Deter,mined in; an Open System

l,ight intensity wvas 1800 ft-c and the gas phase w%,as

21 % O0

Ternperature

Apparent

CO, evolution

photosynthesis in darkness

deg

ug CO., hr-I cll-2 a.y CO. hr-1 cm 2

20

103 ? 2.21

25

106 ? 2.0

13 + 1.0

30

104 ? 2.0

18 + 1.2

35

100 ? 2.1

22 ? 1.5

40

90 ? 2.8

27 ? 1.8

Mfean + S.D. of 3 leaves.

Table IV. Effect of Temiiperatuire on the Rates of Apparent Photos vitthesis. 7rue' P'hotosynthesis, ('O, Evolutioni

in Light and in Darkness of Attached Leaves of Several Plant Species

Light intensity was 1800 ft-c and the gas phase was 21 % O.-

CO., Evolution in CO., Evolution in

A

True'

.l)l)a renit

light

(larkiiess

Temperature

photosynthesis' photosynthesis

(A)

(B)

B

deg

ugq (02

ay ('C).,

,Ag (0O.,

C.y(i(),

Ratio

hIr I cm-

hir cunIt

hr ' cmi--' hr 'I cm-

Soybean

2()

103

82 ? 2.02

21 ? 2.02 11 ? 1.2,'

1.90

25

102

76 ? 3.0

26 ? 3.0 16 +? 2.0

1.62

30

96

66 ? 3.0

30 ? 3.0 24 ? 2.0

1.25

35

85

54 3.4

31? 2.0 32 + 1.2

0.97

40

71

41 4.3

30 1.2 41 ? 1.5

0.73

jackbean

20

98

76 5.0

22 ? 1.8 16 1.2

1.37

25

97

68 8.0

29 ? 2.0 22 2.0

1.32

30

94

61 ?7.1

33 ? 2.0 29 2.0

1.14

351"

88

s50?9.0

38 ? 4.0 36? 1.4

1.05

40

75

3(1 + 9.0

36 5.0 44 ? 2.0

0.82

Water Melon

20

111

90 -+ 2.6

21 ? 2.0 12 - 2.0)

1.75

25

116

88 ? 1.8

28 ? 2.8 19 3.0

1.47

30

113

79 ? 2.4

34 ? 2.8 28 2.0

1.21

35

107

70 ? 1.5

37 ? 2.0 37 t. 6.0

1.00

40

85

49 -- 1.5

36 ? 3.5 4 5 -- 4.0

0.80

Egg plant

20

142

120 it 2.5

22 - 1.2

1(6 -+- 1.2

1.36

25

138

110 ? 3.0

28 ? 1.2 22 + 1.2

1.27

30

131

95 ? 3.0

36 + 1.8 29 + 1.3

1.24

35

112

75 ? 3.0

37 + 2.5 37 ? 2.5

1.00

40

80

49 + 3.5

31 ? 2.5 42 ? 2.0

0.74

1 Apparent photosynthesis + CO, evolution in light. 2 Mean +t S.D. of 3 leavo

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HEW ET AL.-EFFECT OF TEMPERATURE ON PHOTOSYNTHESIS AND C02 EVOLUTION OF LEAVEs 675

100

80C

N

,E

.0 (

60 _

0

40

00

o'

CX

0

20

+-+Leat *,- Leat 2

-i71/7/l /-

S

20 25 30 35 40 Temperature ?C

FIG. 4. Effect of temperature on the magnitude of

the postillumination CO2 outburst in darkness by attached sunflower leaves, as measured in a closed system. Previous light intensity was 1800 ft-c and the gas phase was 21 % 02-

and 350. At 400, a significant decrease in the rate of apparent photosynthesis was observed. The rate of CO2 evolution in darkness increased continuously with increasing temperature up to 40?.

Discussion

The dark respiration rate of most leaves can be reliably measured at physiological .temperatures (19). The measuremnent of the rate of CO., production by leaves in the light, however, is complicated because of the problems of refixation of CO2 'by photosynthesis (24) and by changes in the resistance of the diffusion pathway for CO2 from the cell.s to the external atmosphere. At best, as reviewed briefly in the previous paper (15), only an unknown portion of total CO2 production is measured as CO2 evolution into the environment and any measurable effect of temperature on this rate of CO. evolution must be a net result of the effects of temperature on the rate of CO2 production, the rate of photosvnthes.is and the changes in stomatal resistance.

If 'photosynthesis was n'ot grossly impaired, a closure of stomata, with the consequent increase in

resistance to CO, diffusion would result in a lower

rate of CO2 evolution to the environment even though

the rate of production remained the same or in-

creased. Transpiration or stomatal apertures were

not measured in these investigations but the plants were well supplied with water and no noticeable

signs of water deficit were apparent. In addition, as many investigators e(21, 26.,30, 32) have shown, stomatal apertures become greater with increase of

temperature and wide stomatal apertures are apparent in leaves in the light in C02-free air (21). It seems unlikely. therefore, that the changes in CO2 evolution in the light that we record in this paper are the result of changes in stomatal aperture but rather

they reflect changes either in CO. production or

fixation by the leaf cells. In the temperature range 20 to 300, CO2 evolu.tion

in the light increased wi.th increasing temperature and exceeded the rate of dark respiration. At 350 and 1800 ft-c light the rate of CO2 evolution in the light and darkness were equal but since the rate of CO. evolution in the light is dependent on light intensity (6, 15, 17, 18) the point of intersection was influenced by the light intensity (Fig. 2). Above 350 the rate of CO2 evolution in the light remained the same or decreased and was now less than the dark respiration rate. A similar response to temperature was observed in the size of the post-illumination dark CO. outburst. Decker (3) had previouslv observed a 3 fold increase in the size of the

post-illumination dark CO. outburst when the temperatture was increased from 17.50 to 35.5o. If, as

has been -suggested previously ( 1, 2, 6, 9, 27, 28). the dark outh.urst is a remnant of CO2 evolution in the light the 2 patterns agree and make it probable that the measurement of CO, evolution in the light does, in fact, reflect the CO2 production of the leaf. If this is so, although there are other explanations, the different temperature response patterns and Q10's of CO2 evolution in the light and dark lead one to conclude that they are the result of 2 different processes in the dicotyledonous plants studied.

When 'true' photosynthesis was calculated as the sum of apparent photosynthesis and CO2 evolution in darkness, as was done previously by Stalfelt (25) an'd Egle and Schen'k (5). the decrease in 'true' photosvnthesis with increasing temperature was much less, especially at 400, than when 'true' photosynthesis was calculated as -the sum of apparent photosynthesis and CO2 evolution, in light. It should be noted, however, that 'true' photosynthesis calculated in the latter man,ner did remain fairly constant within the tempera.ture ranige of 20 to 350 and that the rate of photosynthesis in corn, which does not evolve CO., in the light (see 15) also remained constant over this tenmperature interval. With increasing temperature there was also an increase in the CO2 compen-

sation poin,t of the plant leaves as has been observed

previously by many workers (4.5, 12, 20,31, 33). In the temperature range 20 to 340 however, there was little chan'ge in the carlboxylation efficiency of photo-

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