effect of light intensity, carbon dioxide concentration ...provide for the maximum rate of...

Journal of Experimental Botany, Vol. 28, No. 102, pp. 84-95, February 1977

Effect of Light Intensity, Carbon DioxideConcentration, and Leaf Temperature on GasExchange of Spray Carnation Plants

H. Z. ENOCH AND R. G. HURD1

Division of Agricultural Meteorology, Agricultural Research Organization.The Volcani Center, P.O. B.6, Bet Dagan, Israel.

Received 17 April 1976

ABSTRACT

The rates of CO2 assimilation by potted spray carnation plants (cv. Cerise Royalette) weredetermined over a wide range of light intensities (45-450 W m~2 PAR), CO2 concentrations(200-3100 vpm), and leaf temperatures (5-35 °C). Assimilation rates varied with these factorsin a way similar to the response of single leaves of other temperate crops, although the abso-lute values were lower. The optimal temperature for CO2 assimilation was between 5 and 10 °Cat 45 W m~2 PAR but it increased progressively with increasing light intensity and CO2 con-centration up to 27 °C at 450 W m~2 PAR and 3100 vpm CO2 as expressed by the equation2\>pt = —6-47 + 2-336 In C + 0-031957 where C is CO2 concentration in vpm and I is photo-synthetically active radiation in W m~2. CO2 enrichment also increased stomatal resistance,especially at high light intensities.

The influence of these results on optimalization of temperatures and CO2 concentrations forcarnation crops subjected to daily light variation, and the discrepancy between optimal tem-peratures for growth and net photosynthesis, are discussed briefly.

INTRODUCTION

It is possible to effect some control over temperature and CO2 concentration in theglasshouse, with the purpose of increasing production. As a basis for setting upthese conditions, it has been proposed that optimal yield will result when theseparameters are continually adjusted to the intensity of the incoming light so as toprovide for the maximum rate of photosynthesis (Lake, 1966). The present workpresents information on the effects of temperature, CO2 concentration, and lightintensity, on the net photosynthesis of whole plants so as to enable this proposalto be tested.

In an earlier paper (Hurd and Enoch, 1976), some aspects of the photosynthesisand growth of spray carnation plants were considered. The spray carnation wasagain chosen here, both because of its commercial importance and, more important-ly, also because its photosynthesis was shown to be unaffected by its previous tem-perature history, making the task of determining the optimal environmental factors

1 Present address: Dept. of Plant Physiology, Glasshouse Crops Res. Inst., Littlehampton, Sussex,U.K.

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Enoch and Hurd—Gas Exchange in Carnations 85

technically relatively simple. It also means that when adjustments to the environ-ment are subsequently made in the glasshouse, interactions with earlier temperatureregimes, as observed in other plants, will be unlikely (see Discussion).

MATERIALS AND METHODSRooted cuttings of spray carnation plants (Dianthus caryophyllus L. cv. Cerise Royalette)were planted in November in 9 cm plastic pots containing coarse sand free of organic matterand grown for 1-2 months until the one-sided leaf area was 1-2 dm2. The plants were grown ina greenhouse at ambient atmospheric CO2 concentration and day/night temperatures of 20/10 °C. Daily watering was with complete nutrient solution and illumination was supplementedby two 400 W HPLR Lamps (Philips, Eindhoven, The Netherlands) providing a total radia-tion flux density of 350-400 W m~2 PAR for 12 h daily. This high-light pretreatment was usedto obtain plants that could give a constant net photosynthetic rate with time and little hystere-sis to temperature changes during the day (see Results and Discussion).

The apparatus used for measurement of net photosynthesis, dark respiration, and trans-piration rate was a conventional semi-open system, similar to that described previously (Hurdand Enoch, 1976). The CO2 exchange was calculated from the rate of air through-flow and thedifference in CO2 concentrations in up- and downstream air as measured in the differentialmode by an URAS 2 (Hartmann and Braun, Frankfurt/Main, BRD). The CO2 concentrationin the assimilation chamber was also measured by an URAS 2, used in the absolute mode.Both CO2 analyses were recalibrated each hour with a calibration gas produced by three,SA 27/3a air-mixing pumps (Wosthoff, Bochum, BRD). Transpiration was calculated fromthe up- and downstream dew-points as measured by a 'thermoelectric dew-point hygrometer'(MK 3, Salford Electrical Instruments Ltd., England). Illumination was from two 400 WHPLR lamps that could provide up to 450 W m~2 PAR; (light intensities were lowered byintroducing layers of aluminum net between the lamps and the assimilation chamber). Thechamber itself essentially comprised two inverted, concentric beakers between the walls ofwhich water of known temperature could be circulated. By adjusting the water temperatureover the range 1-35 °C leaf temperature could be controlled between 10 and 35 CC, independentof the radiation flux density.

A plant to be used for gas exchange measurements was transferred at 1700 (local time)from greenhouse to laboratory where it was watered and then drained for ] 0 min; the exposedsoil surface was covered with expanded polystyrene and the pot wrapped in thermal insulationmaterial (to minimize energy transfer and evaporation while allowing O2 and CO2 gas diffusionfrom the root zone). The plant was placed in the assimilation chamber and the leaf tempera-ture adjusted to 20 CC. A CO2 concentration and light intensity appropriate to the followingday's experiment was provided, as was a root temperature of 20 + 2 °C, that was maintainedduring the measurements. Illumination only was interrupted from 1900 to 0500 of the fol-lowing day. Net photosynthesis and transpiration rates were measured approximately 3 hafter the lights were switched on the following morning when the rates had been constant for20 min. The leaf temperature was then slowly changed (c. 0-3 °C min-1) from 20 to either 10 °Cat high light or 5 °C at low light, and gas exchange rates were measured when they had re-mained stable for 15 min. Measurements were repeated for each 5 °C at higher leaf temperaturesup to 35 °C, whereupon the leaf temperature was brought back to 20 °C. The gas exchangedata piesented for 20 °C were the means of the three values obtained. The lamps were thenswitched off and the dark respiration rate was determined for 1 h at a leaf temperature of 20 CC.The plant was finally removed from the chamber and its dimensions were recorded by destruc-tive sampling, as described previously (Hurd and Enoch, 1976). Thus one plant was used foreach combination of PAR and CO2 concentration and the leaf temperature of that plantwas changed over the experimental ranges.

While leaf temperature was changed over the range of 5-35 °C or 10-35 °C, the dew-pointsof air entering the chamber were constant at respectively 4 or 6 °C, hence water vapour deficitchanged between 0-3 and 4-7 kPa. In some cases, especially at low CO2 concentrations, trans-piration appeared to be in a transient state although CO2 uptake was constant; in such cases thetransient transpiration rate was recorded at the end of the 15 min period but the result wasnot used for calculation of stomatal resistance.

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86 Enoch and Hurd—Gas Exchange in Carnations

RESULTSPreliminary experimentsThe plant-to-plant variation with respect to net photosynthetic rate (F) was in-vestigated in a preliminary experiment. Nine pairs of plants were used, that hadbeen grown outdoors at a mean photosynthetically active radiation (PAR) of about220 W m~2 for 12 h per day during 1-2 months. F was measured at ambient atmos-pheric CO2 concentration, 20 °C leaf temperature, and 450, 125, and 45 W m~2

PAR, respectively. The mean numerical deviation of F from F was ±0-65 mg CO2dm~2 h"1 and was smaller than the estimated accuracy of the measuring method.The mean CO2 uptake changed less than 0-1 mg dm~2 h"1 per day over a period of3 weeks.

A second preliminary study was made of the effect of time of day, and of the num-ber of hours plants were subjected to a particular environment, on the rate of netphotosynthesis. At temperatures up to 25 °C, any combination of light intensityand CO2 concentration gave constant net photosynthetic rates throughout an 8 hday using plants grown at high light intensities (350-400 W m~2 PAR). At tempera-tures of 30-35 °C in high light and with a low CO2 concentration (that is, con-ditions leading to high transpiration rates), the plants tended to wilt and in this caseCO2 uptake decreased after 1-2 h. Increasing the CO2 concentration tended tosuppress this fall-off in CO2 uptake.

The effect of leaf temperature history in the hours immediately precedingmeasurement was also determined. Net photosynthesis came to equilibrium rapidlywithout showing any hysteresis when leaf temperatures were changed at a rate of0-3 °C min"1 or less, within the range 5-35 °C. Figure 1 shows an example of measure-ments lasting about 11 h in which temperature was changed from 20 to 35 °C,back to 13 °C, and then increased to 32 °C, and lowered to 24 °C. The plant had a

25

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IU 15 20 25Leaf temperature (°C)

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PIG. 1. The repeatability of CO2 assimilation in a carnation plant submitted to a series oftemperature changes over the course of 11 h. CO2 concentration, 350 vpm; light intensity,

450 W m-2; Leaf area, ~ 1 dm2.

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leaf area of about 1 dm2. Hysteresis was less than ±1 mg CO2 h~x per plant, whichwas similar to the measuring accuracy of the system. At high light intensity andlow CO2 concentration the best reproducibility was obtained when plants werekept only 5-10 min at each of the high temperatures (30 and 35 °C). This procedurewas followed subsequently.

Three plants were used to investigate the influence of the previous day's irradianceon dark respiration (2?D) and the relative change in B& to a 10 °C increase in tem-perature (Qio). A plant was placed in the assimilation chamber at 1700 (localtime) at 360 vpm CO2, 20 °C leaf temperature, and 45, 125, or 450 W m"2 PAR.The lamps were switched off between 1900 and 0400, and at 1200, givingthe plants an 8 h light period. In the succeeding night, leaf temperature wasdecreased to 5 °C and then increased to 35 °C within 1 h, in which i?D was measuredat 5 °C intervals. Thereafter the plant was removed from the assimilation chamberand its leaf area determined by destructive sampling. At any temperature, the abso-lute values of BD were dependent upon the previous light level, reflecting theamounts of respirable photosynthates (Fig. 2). Log BT> was a linear function oftemperature, with almost the same slope for all three prior light regimes. TheQ10 was 1-95, 1-93, and 2-12 respectively, for 45, 125, and 450 W m~2 PAR. Foreach combination of light intensity and CO2 concentration in the main experiment(see below) the mean Qio of 2-0 was used, together with the values of J?D at 20 °C.

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FIG. 2. Dark respiration rate of carnation plants at different leaf temperatures. Values re-corded during the first hour after lamps were switched off, following days with light intensity of

450 ( ), 125 ( ), or 45 W m~2 PAR ( ).

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to estimate R& values at the different temperatures during the preceding lightperiod.

Main experimentsNet photosynthetic rate of the whole plant (F) was measured in the environmentalconditions: 45, 125, 280, or 450 W m~2 PAR at each of the CO2 concentrations 200,350, 700, 1500, and 3100 vpm and, at the leaf temperatures of 10 (or 5), 15, 20, 25,30, and 35 °C. In Fig. 3A, B, C, D, and E, two curves are given for each environmentalcondition: the one with experimental points gives the F value obtained; the oneabove, with the same line designation, has the appropriate ifo value added to F.The value for F at 20 °C was obtained three times (as described) for each of the 20plants. The mean numerical deviation of F from F in the three measurements was0-62 mg CO2 dm-2 hr1.

10 i; 20Leaf temperature (°C)

FIGURE 3A

25 30 35

FIG. 3. CO2 assimilation rate (F) by carnation plants in relation to light intensity, leaf tem-perature, and CO2 concentration. Lines with symbols represent the original F values; lineswithout symbols represent F + dark respiration rate RD. Arrow indicates optimal tem-perature for maximal F within a given light and CO2 regime. Light intensities: 450 ( ),280 ( ), 125 ( ), 45 W m~2 PAR ( ). CO2 concentrations (vpm): A, 200; B, 350;

c, 700; r>, 1500; E, 3100.

F increased with light and CO2 concentration at all temperatures to a maximumrate of 45 mg CO2 dm"2 h"1 at 450 W m"2 PAR, 3100 vpm CO2, and at a temperatureof 25 °C. At the lowest light intensity, maximum net photosynthesis (Fmax) wasobtained at the lowest temperatures used, at all CO2 concentrations. As light in-tensities and CO2 concentrations were raised, -Pmax was reached at progressivelyhigher temperatures (Fig. 4).

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Enoch and Hurd—Gas Exchange in Carnations

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In general, when allowance was made for CO2 losses by dark respiration, the sumof F and RD remained relatively constant at supraoptimal temperatures regard-less of the light or CO2 conditions. This corrected F value is not the same as grossphotosynthesis, since it does not include a correction for that component of respira-tion which takes place in light only.

To give an indication of the effect of CO2 concentration on stomatal aperture,leaf resistance to water vapour transport was calculated at different substomatalCO2 concentrations at 20 °C leaf temperature, from measurements of CO2 and watervapour fluxes. Data from total radiations of 148 W m~2 (125 W m~2 PAR) and 535W m~2 (450 W m~2 PAR), that were obtained about 3 h after the lamps were lit,and where gas exchange rates had reached equilibrium, are presented in Fig. 5.Each point represents unreplicated measurements on a different plant. At a ~ 300vpm CO2 concentration within the substomatal cavity, leaf resistance was less atthe higher light intensity than at the lower one. With increasing CO2 concen-

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Enoch and Hurd—Gas Exchange in Carnations

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tration, leaf resistance increased at a steeper rate at the higher light intensity,giving a leaf resistance to water vapour transfer of 6-6 s cm"1 at substomatal CO2levels above 2400 vpm (equivalent to an external concentration of 3100 vpm).

DISCUSSIONThe rates of carbon assimilation by carnation plants (Fig. 3) are appreciably lowerthan those for single leaves of other temperate crops. This is most noticeable atlow light intensities, in which the rates are 2—3 mg CO2 dm"2 h"1 at 45 W m~2, com-pared with values of 10-20 mg CO2 dm~2 h - 1 given by Gaastra (1959) for sugar beetand turnip. Even at higher light intensities its values are still only about half thoseobtained for sugar beet and turnip by Gaastra (1959), for cotton by Bierhuizen

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100 500200 .100 400Light intensity (W m~ 2 PAR)

FIG. 4. The temperature optimum for net photosynthesis of carnation plants at differentlight intensities and CO2 concentrations (derived from Fig. 3). CO2 concentration (vpm):

3100 (A A), 1500 ( • • ) , 700 ( • • ) , 350, (• • ) , 200 (O O).

~ 4

0,0 30001000 2000

Substomatal CO, concentration (parts I0"6)F I G . 5. Leaf resistance of carnation at different substomatal CO2 concentrations and light in-tensities of (o O) 148 W m- 2 (125 W m-2 PAR) and ( • • ) 535 W m~2 (450 W rrr 2

PAR) total radiation.

and Slatyer (1964), and for soybean by Brun and Cooper (1967). Photosynthesisincreased substantially with CO2 enrichment. At 20 °C, for example, an approxi-mately four-fold enrichment from ambient CO2 levels increased photos3rnthesis byabout 60 per cent at three widely different light intensities (Fig. 6). The equivalentincreases obtained by Gaastra (1959), Bierhuizen and Slatyer (1964), and Brunand Cooper (1967) in these conditions were even greater, i.e., about 100 per cent.The difference between these sets of results and the carnation data is presumablyaccounted for by the considerable respiratory load of the rest of the carnation plant.Since a component of respiration (maintenance and root respiration) is not de-pendent on light intensity, net CO2 uptake will be depressed progressively more at

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Enoch and Htird—Gas Exchange in Carnations

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Leaf temperature (°C)FIG. 6. The effect of CO2 enrichment on net photosynthesis of carnation at 45, 125, and 450W m~2 PAR (numbers on figure) at different temperatures (derived from Fig. 3). 1500 vpm

CO2 ( ); 350 vpm CO2 ( ).

low light intensities. The carnation also has a small leaf area for a given total plantweight (for example, leaf area/total dry weight is typically only one quarter of thatfor similarly grown tomato plants). This will tend to emphasize the difference be-tween net CO2 assimilation on a leaf area basis compared with a whole plant basis.The carnation is also less efficient at light interception than many other plants be-cause of its relatively thick leaves, partly adpressed against the stem.

Temperature had a marked effect on F, especially at higher rates of photosyn-thesis. An optimum temperature in the 15-25 °C range has often been obtained fortemperate crop plants (Murata and Iyama, 1963; Zelitch, 1971) and clearly thecarnation comes near the bottom of this range, at ambient atmospheric CO2concentrations. The temperature (Topt) at which maximal net photosynthesis wasobtained increased with an increase in either light intensity or CO2 concentrationwith apparently little interaction between the two factors, suggesting they areassociated with different processes (Fig. 4). A similar finding is reported by Stalfelt(1960), referring to Lundegardh's work on Solanum tuberosum. Such a response iscompatible with the fact that photosynthesis depends on both a temperature-independent light-capture process and a temperature-dependent CCVfixationprocess requiring no light (Heath, 1969, quoting Emerson and Arnold, 1932).

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Thus, at low light intensity photosynthesis is relatively independent of tem-perature, but as the light intensity and/or CO2 concentration increases, progressivelyhigher temperatures are required to prevent the dark process from becoming limit-ing. Net photosynthesis of the whole plant is the result of gross photosynthesis lessrespiration during photosynthesis, i.e., light respiration, and that fraction of darkrespiration which is not suppressed by light (for instance, maintenance and rootrespiration).

Losses of CO2 in dark respiration were dependent on temperature and the previousday's light conditions. A similar correlation was found by Ludwig, Saeki, and Evans,(1965). When these repiratory CO2 losses were added to the previous day's CO2assimilation values, the resulting level of CO2 fixation was reasonably constant abovethe optimal temperature for photosynthesis. This suggests that gross photosynthesisless light respiration (as opposed to dark respiration) remains almost constant inthe temperature zone where it is no longer limited by the rate of the dark CO2-fixation process.

Gaastra (1959) concluded that CO2 enrichment was worthwhile only at high leaftemperatures, regardless of the light intensity. The data of Fig. 6 show that, forcarnation, this appears true at high light intensity only, where the rate of the darkreaction had an overriding control of photosynthesis at low temperature. When thelight intensit}' was 125 W m~2 or less, CO2 enrichment was equally beneficial at alltemperatures, at least down to 10 °C.

Another effect of CO2 enrichment is as an anti-transpirant. The data of Fig. 5indicate that CO2 is more effective in this role at high light intensity. With CO2enrichment, leaf resistance increased four-fold at high light intensity but onlytwo-fold at the lower intensity.

The original purpose of this study was to obtain the optimal combination oftemperature and CO2 concentration which would maximize photosynthesis inglasshouse conditions to accord with prevailing light. This purpose was achieved.Figure 3 illustrates the relevant data while Fig. 4 gives the optimal leaf temperaturefor photosynthesis as varying CO2 concentrations and light intensities. As can beseen from Fig. 4, optimal temperatures (Topt) for maximal net photosynthesis(F) at given CO2 concentrations are almost linear functions of light intensity (/).Furthermore, a doubling of CO2 concentration (C) increases TOpt by a nearlyequal amount at all light intensities and consequently an equation of the form

TOpt = «i + «2 In C + asl

represents the data well. The constants a\, «2, and a% can be determined by the least-squares procedure. This gave the following empirical equation for the optimaltemperature as a function of C and / :

y o p t = -6-47 + 2-336 In G + 0-03195/

where TOpt is expressed in °C, C as vpm CO2, and / as W m~2 PAR.Caution must be exercised in applying these results for determining optimal

greenhouse conditions for production of carnation cuttings or flowers. A difficultyin providing climatological guidelines rests on several observations that optimaltemperatures for photosynthesis are related to prior temperatures at which the

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plants were grown (Mooney and Harrison, 1970; Downton and Slatyer, 1972;Sawada and Miyachi, 1974). Such dependence was not found in the carnation(Hurd and Enoch, 1976), but even then use of our data for predicting the photo-synthesis of a greenhouse carnation crop involves considerable extrapolationbecause of differences in plant material, age, spacing, culture, etc. Only the generaltrend of the experimental data is therefore relevant and for this reason we haveaccepted some variability arising from the lack of replication.

There is another aspect to be considered before one could recommend growingplants at the temperatures optimal for photosynthesis. The low temperatures re-quired at low light intensities and ambient atmospheric CO2 concentrations areunlikely to be optimal for growth. The fact that dark respiration increases exponen-tially with temperature implies that available energy for growth processes will alsoincrease with temperature.

From these considerations it appears that the original concept of controllingconditions for maximum photosynthesis of a crop of given leaf area and thus lightinterception, is insufficient. It must be supplemented with further information onoptimal environmental conditions for growth of different plant organs so thatthe basis necessary for determining optimal greenhouse climates can be provided.

ACKNOWLEDGMENTSWe wish to thank Dr. M. Buckbinder, A.R.O., Division of Agricultural Meteoro-logy, for his assistance with the gasometric analysis, and Mr. E. Ephrat and Dr.Y. Ben-Yaacov of the A.R.O., Division of Ornamental Crops, for providing plantmaterial and assistance in growing it.

LITERATURE CITEDBIERHUIZEN, J. F., and SLATYER, R. O., 1964. Aust. J. biol. Sci. 17, 348-59.BRUN, W. A., and COOPER, R. L., 1967. Crop Sci. 7, 451-4.DOWNTON, J., and SLATYER, R. O., 1972. PL Physiol., Lancaster, 50, 518-22.GAASTRA, P., 1959. Meded. LandbHoogesch. Wageningen, 59, 1-68.HEATH, O. V. S., 1969. The physiological aspects of photosynthesis. Heinemann, London. Pp.

214 et sea.HUBD, R. G. and ENOCH, H. Z., 1976. J. exp. Bot. 27, 695-703.LAKE, J. V., 1966. Nature Lond. 209, 97-8.LUDWIO, L. J., SAEKI, T., and EVANS, L. T., 1965. Aust. J. biol. Sci. 18, 1103-18.MOONEY, H. A., and HARRISON, A. T., 1970. Proc. IBP/PP Tech. Meeting Trebon, 1969. Ed.

I. Setlik. Centre Agric. Publ. and Doc, Wageningen. Pp. 411-17.MUBATA, Y., and IYAMA, J., 1963. Proc. Crop Sci. Soc. Japan, 31, 315-22.SAWADA, S., and MIYACHI, S., 1974. PL Cell Physiol., Tokyo, 15, 111-20.STALFELT, M. G., 1960. Encyl. PL Physiol. Ed. W. Ruhland. Springer Verlag. Berlin, Vol. 2,

pp. 101 et seq.ZELITCH, I., 1971. Photosynthesis, photorespiration and plant productivity. Academic Press,

New York. Pp. 244 et seq.

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