Temperature acclimation in a biochemical model of photosynthesis: a reanalysis of data from 36 species

The Farquhar et al. model of C(3) photosynthesis is frequently used to study the effect of global changes on the biosphere. Its two main parameters representing photosynthetic capacity, V(cmax) and J(max), have been observed to acclimate to plant growth temperature for single species, but a general formulation has never been derived. Here, we present a reanalysis of data from 36 plant species to quantify the temperature dependence of V(cmax) and J(max) with a focus on plant growth temperature, i.e. the plants' average ambient temperature during the preceding month. The temperature dependence of V(cmax) and J(max) within each data set was described very well by a modified Arrhenius function that accounts for a decrease of V(cmax) and J(max) at high temperatures. Three parameters were optimized: base rate, activation energy and entropy term. An effect of plant growth temperature on base rate and activation energy could not be observed, but it significantly affected the entropy term. This caused the optimum temperature of V(cmax) and J(max) to increase by 0.44 degrees C and 0.33 degrees C per 1 degrees C increase of growth temperature. While the base rate of V(cmax) and J(max) seemed not to be affected, the ratio J(max) : V(cmax) at 25 degrees C significantly decreased with increasing growth temperature. This moderate temperature acclimation is sufficient to double-modelled photosynthesis at 40 degrees C, if plants are grown at 25 degrees C instead of 17 degrees C.     

The effect of temperature on C(4)-type leaf photosynthesis parameters

C(4)-type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters - the maximum catalytic rate of the enzyme ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) (V(cmax)), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (V(pmax)) and the maximum electron transport rate (J(max)) - were examined. Maize plants were grown in climatic-controlled phytotrons, and the curves of net photosynthesis (A(n)) versus intercellular air space CO(2) concentrations (C(i)), and A(n) versus photosynthetic photon flux density (PPFD) were determined over a temperature range of 15-40 degrees C. Values of V(cmax), V(pmax) and J(max) were computed by inversion of the von Caemmerer & Furbank photosynthesis model. Values of V(pmax) and J(max) obtained at 25 degrees C conform to values found in the literature. Parameters for an Arrhenius equation that best fits the calculated values of V(cmax), V(pmax) and J(max) are then proposed. These parameters should be further tested with C(4) plants for validation. Other model key parameters such as the mesophyll cell conductance to CO(2) (g(i)), the bundle sheath cells conductance to CO(2) (g(bs)) and Michaelis-Menten constants for CO(2) and O(2) (K(c), K(p) and K(o)) also vary with temperature and should be better parameterized.     

供氮和增温对倍增二氧化碳浓度下荫香叶片光合作用的影响

供给0～0.6 mg N的盆栽荫香(Cinnamomum burmannii)幼树分别生长在倍增CO ₂(+CO₂,731 μmol·mol^-1)和正常空气CO ₂浓度(CO ₂,365 μmol·mol^-1)的生长箱内,昼夜温度分别为25/23 ℃和32/25 ℃,自然光照下生长30 d.以生长在CO₂和25/23 ℃下的植株为对照研究增温和氮对+CO₂叶片光合作用的影响.结果表明,在+CO₂和25/23 ℃下无氮和氮处理植株的平均光合速率(Pnsat)较+CO₂和32/25 ℃下的叶片高5.1%,温度增高降低叶片Pnsat;而Pnsat随供氮而增高.在+CO₂条件下,生长在32/25 ℃下的叶片Rubisco最大羧化速率(Vcmax)和最大电子传递速率(Jmax)较25/23 ℃下的低(P＜0.05),温度增高降低+CO₂下叶片的Vcmax和Jmax在+CO2下叶片光合呼吸速率(Rp)较低,生长温度增高提升Rp.在CO₂下生长温度从25/23 ℃增至32/25 ℃,叶片的Rubisco含量(NR)和Rubisco活化中心浓度(M)降低,而供氮能增高NR和M.供氮能减缓温度增高对倍增CO₂下荫香叶片光合作用的限制.     

Seasonal changes in temperature dependence of photosynthetic rate in rice under a free-air CO(2) enrichment

BACKGROUND AND AIMS: Influences of rising global CO(2) concentration and temperature on plant growth and ecosystem function have become major concerns, but how photosynthesis changes with CO(2) and temperature in the field is poorly understood. Therefore, studies were made of the effect of elevated CO(2) on temperature dependence of photosynthetic rates in rice (Oryza sativa) grown in a paddy field, in relation to seasons in two years. METHODS: Photosynthetic rates were determined monthly for rice grown under free-air CO(2) enrichment (FACE) compared to the normal atmosphere (570 vs 370 micromol mol(-1)). Temperature dependence of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (V(cmax)) and the maximum rate of electron transport (J(max)) were analysed with the Arrhenius equation. The photosynthesis-temperature response was reconstructed to determine the optimal temperature (T(opt)) that maximizes the photosynthetic rate. KEY RESULTS AND CONCLUSIONS: There was both an increase in the absolute value of the light-saturated photosynthetic rate at growth CO(2) (P(growth)) and an increase in T(opt) for P(growth) caused by elevated CO(2) in FACE conditions. Seasonal decrease in P(growth) was associated with a decrease in nitrogen content per unit leaf area (N(area)) and thus in the maximum rate of electron transport (J(max)) and the maximum rate of RuBP carboxylation (V(cmax)). At ambient CO(2), T(opt) increased with increasing growth temperature due mainly to increasing activation energy of V(cmax). At elevated CO(2), T(opt) did not show a clear seasonal trend. Temperature dependence of photosynthesis was changed by seasonal climate and plant nitrogen status, which differed between ambient and elevated CO(2).     

Seasonal change in the balance between capacities of RuBP carboxylation and RuBP regeneration affects CO2 response of photosynthesis in Polygonum cuspidatum

The balance between the capacities of RuBP (ribulose-1,5-bisphosphate) carboxylation (V(cmax)) and RuBP regeneration (expressed as the maximum electron transport rate, J(max)) determines the CO(2) dependence of the photosynthetic rate. As it has been suggested that this balance changes depending on the growth temperature, the hypothesis that the seasonal change in air temperature affects the balance and modulates the CO(2) response of photosynthesis was tested. V(cmax) and J(max) were determined in summer and autumn for young and old leaves of Polygonum cuspidatum grown at two CO(2) concentrations (370 and 700 micromol mol(-1)). Elevated CO(2) concentration tended to reduce both V(cmax) and J(max) without changing the J(max):V(cmax) ratio. The seasonal environment, on the other hand, altered the ratio such that the J(max):V(cmax) ratio was higher in autumn leaves than summer leaves. This alternation made the photosynthetic rate more dependent on CO(2) concentration in autumn. Therefore, when photosynthetic rates were compared at growth CO(2) concentration, the stimulation in photosynthetic rate was higher in young-autumn than in young-summer leaves. In old-autumn leaves, the stimulation of photosynthesis brought by a change in the J(max):V(cmax) ratio was partly offset by accelerated leaf senescence under elevated CO(2). Across the two seasons and the two CO(2) concentrations, V(cmax) was strongly correlated with Rubisco and J(max) with cytochrome f content. These results suggest that seasonal change in climate affects the relative amounts of photosynthetic proteins, which in turn affect the CO(2) response of photosynthesis.     

Photosynthetic performance at low temperature of Bouteloua gracilis Lag., a high-altitude C4 grass from the Rocky Mountains, USA

The mechanisms controlling the photosynthetic performance of C₄ plants at low temperature were investigated using ecotypes of Bouteloua gracilis Lag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700 μ mol m^?2 s^?1 and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO₂ assimilation rate (A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO₂‐saturated rate of photosynthesis to decline to a greater degree than the initial slope of A versus the intercellular CO₂ response, thereby reducing the photosynthetic CO₂ saturation point. As a consequence, A in normal air was CO₂‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higher A; however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum, A in high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, while A in low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adapted F_v/F_m. In both ecotypes, the activity of Rubisco was equivalent to A below 17 °C but well in excess of A above 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco and A, we propose that Rubisco is a major limitation on C₄ photosynthesis in B. gracilis below 17 °C. Based on these results and for theoretical reasons associated with how C₄ plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C₄ photosynthesis at low temperature.     

Grazing alters warming effects on leaf photosynthesis and respiration in Gentiana straminea,an alpine forb species

Aims Vast grasslands on the Tibetan Plateau are almost all under livestock grazing. It is unclear, however, what is the role that the grazing will play in carbon cycle of the grassland under future climate warming. We found in our previous study that experimental warming can shift the optimum temperature of saturated photosynthetic rate into higher temperature in alpine plants. In this study, we proposed and tested the hypothesis that livestock grazing would alter the warming effect on photosynthetic and respiration through changing physical environments of grassland plants.Methods Experimental warming was carried by using an infrared heating system to increase the air temperature by 1.2 and 1.7°C during the day and night, respectively. The warming and ambient temperature treatments were crossed over to the two grazing treatments, grazing and un-grazed treatments, respectively. To assess the effects of grazing and warming, we examined photosynthesis, dark respiration, maximum rates of the photosynthetic electron transport (J max), RuBP carboxylation (V cmax) and temperature sensitivity of respiration Q 10 in Gentiana straminea, an alpine species widely distributed on the Tibetan grassland. Leaf morphological and chemical properties were also examined to understand the physiological responses.Important findings 1) Light-saturated photosynthetic rate (A max) of G. straminea showed similar temperature optimum at around 16°C in plants from all experimental conditions. Experimental warming increased A max at all measuring temperatures from 10 to 25°C, but the positive effect of the warming occurred only in plants grown under the un-grazed conditions. Under the same measuring temperature, A max was significantly higher in plants from the grazed than the un-grazed condition. 2) There was significant crossing effect of warming and grazing on the temperature sensitivity (Q 10) of leaf dark respiration. Under the un-grazed condition, plants from the warming treatment showed lower respiration rate but similar Q 10 in comparison with plants from the ambient temperature treatment. However, under the grazed condition Q 10 was significantly lower in plants from the warming than the ambient treatment. 3) The results indicate that livestock grazing can alter the warming effects on leaf photosynthesis and temperature sensitivity of leaf dark respiration through changing physical environment of the grassland plants. The study suggests for the first time that grazing effects should be taken into account in predicting global warming effects on photosynthesis and respiration of plants in those grasslands with livestock grazing.     

Leaf optical properties reflect variation in photosynthetic metabolism and its sensitivity to temperature

Researchers from a number of disciplines have long sought the ability to estimate the functional attributes of plant canopies, such as photosynthetic capacity, using remotely sensed data. To date, however, this goal has not been fully realized. In this study, fresh-leaf reflectance spectroscopy (λ=450-2500 nm) and a partial least-squares regression (PLSR) analysis were used to estimate key determinants of photosynthetic capacity-namely the maximum rates of RuBP carboxylation (V(cmax)) and regeneration (J(max))-measured with standard gas exchange techniques on leaves of trembling aspen and eastern cottonwood trees. The trees were grown across an array of glasshouse temperature regimes. The PLSR models yielded accurate and precise estimates of V(cmax) and J(max) within and across species and glasshouse temperatures. These predictions were developed using unique contributions from different spectral regions. Most of the wavelengths selected were correlated with known absorption features related to leaf water content, nitrogen concentration, internal structure, and/or photosynthetic enzymes. In a field application of our PLSR models, spectral reflectance data effectively captured the short-term temperature sensitivities of V(cmax) and J(max) in aspen foliage. These findings highlight a promising strategy for developing remote sensing methods to characterize dynamic, environmentally sensitive aspects of canopy photosynthetic metabolism at broad scales.     

Modelling photosynthetic responses to temperature of grapevine (Vitis vinifera cv. Semillon) leaves on vines grown in a hot climate

Field measurements of photosynthesis of Vitis vinifera cv. Semillon leaves in relation to a hot climate, and responses to photon flux densities (PFDs) and internal CO(2) concentrations (c(i) ) at leaf temperatures from 20 to 40 °C were undertaken. Average rates of photosynthesis measured in situ decreased with increasing temperature and were 60% inhibited at 45 °C compared with 25 °C. This reduction in photosynthesis was attributed to 15-30% stomatal closure. Light response curves at different temperatures revealed light-saturated photosynthesis optimal at 30 °C but also PFDs saturating photosynthesis increased from 550 to 1200 μmol (photons) m(-2)s(-1) as temperatures increased. Photosynthesis under saturating CO(2) concentrations was optimal at 36 °C while maximum rates of ribulose 1,5-bisphosphate (RuBP) carboxylation (V(cmax)) and potential maximum electron transport rates (J(max)) were also optimal at 39 and 36 °C, respectively. Furthermore, the high temperature-induced reduction in photosynthesis at ambient CO(2) was largely eliminated. The chloroplast CO(2) concentration at the transition from RuBP regeneration to RuBP carboxylation-limited assimilation increased steeply with an increase in leaf temperature. Semillon assimilation in situ was limited by RuBP regeneration below 30 °C and above limited by RuBP carboxylation, suggesting high temperatures are detrimental to carbon fixation in this species.     

Effects of day and night temperature and temperature variation on photosynthetic characteristics

Net photosynthetic rates and mesophyll conductances were measured under standardized conditions for leaves of two C₃ and one C₄ annual species grown at temperatures of 20 to 32°C. Plants were grown with varying day and night temperatures, and also at constant temperatures equal to all the day and night temperatures used. Plants were grown with 8, 12, and 16 hours of light per day. This design allowed determination of whether photosynthetic characteristics were best correlated with day, night, mean, or time-weighted mean temperatures, The results showed that for Glycine max (L.) Merr. (C₃) night temperature was most important in determining photosynthetic characteristics, while in Helianthus annuus L. (C₃) and Amaranthus hypochondriacus L. (C₄) the time-weighted mean temperature was most important. The results for all species were consistent with the hypothesis that development of photosynthetic characteristics is related to a balance between the rate of leaf expansion and the rate of photosynthesis under the growth conditions.     

The adaptation to temperature of photorespiration and of the photosynthetic carbon metabolism of altitudinal ecotypes of Trifolium repens L.

Summary In altitudinal ecotypes of Trifolium repens L. the oxygen inhibition of photosynthesis, the CO₂ compensation point and the sugar content were examined. Excised leaves were exposed to ¹⁴CO₂ for 20 s and 60 min periods and the radioactivity in different photosynthetic products was studied. In all experiments the temperature during growth and measurement was varied.To some extent, the differences between the ecotypes and the differences between the plants grown under different temperature conditions are similar. These ecotypic differences appear to reflect long-term adaptation to the general temperature conditions at each site. Alpine ecotypes and plants grown at low temperatures show an increased photorespiration. The ¹⁴C-labeling of certain photosynthetic products also changes with the ecotypes and the temperatures during growth. Other differences between the ecotypes are interpreted as adaptations to the partial pressure of Co₂ and to the length of the growing season, both of which change with altitude.The metabolism of photosynthesis depends greatly on temperature. The ¹⁴C-experiments and the study of photorespiration suggest that, to a certain degree, adaptation can compensate for this dependence on temperature.     

Low-temperature photosynthetic performance of a C4 grass and a co-occurring C3 grass native to high latitudes

The photosynthetic performance of C₄ plants is generally inferior to that of C₃ species at low temperatures, but the reasons for this are unclear. The present study investigated the hypothesis that the capacity of Rubisco, which largely reflects Rubisco content, limits C₄ photosynthesis at suboptimal temperatures. Photosynthetic gas exchange, chlorophyll a fluorescence, and the in vitro activity of Rubisco between 5 and 35 °C were measured to examine the nature of the low‐temperature photosynthetic performance of the co‐occurring high latitude grasses, Muhlenbergia glomerata (C₄) and Calamogrostis canadensis (C₃). Plants were grown under cool (14/10 °C) and warm (26/22 °C) temperature regimes to examine whether acclimation to cool temperature alters patterns of photosynthetic limitation. Low‐temperature acclimation reduced photosynthetic rates in both species. The catalytic site concentration of Rubisco was approximately 5.0 and 20 µmol m^?2 in M. glomerata and C. canadensis, respectively, regardless of growth temperature. In both species, in vivo electron transport rates below the thermal optimum exceeded what was necessary to support photosynthesis. In warm‐grown C. canadensis, the photosynthesis rate below 15 °C was unaffected by a 90% reduction in O₂ content, indicating photosynthetic capacity was limited by the capacity of P_i‐regeneration. By contrast, the rate of photosynthesis in C. canadensis plants grown at the cooler temperatures was stimulated 20–30% by O₂ reduction, indicating the P_i‐regeneration limitation was removed during low‐temperature acclimation. In M. glomerata, in vitro Rubisco activity and gross CO₂ assimilation rate were equivalent below 25 °C, indicating that the capacity of the enzyme is a major rate limiting step during C₄ photosynthesis at cool temperatures.     

Growth temperature can alter the temperature dependent stimulation of photosynthesis by elevated carbon dioxide in Albutilon theophrasti

Stimulation of photosynthesis in response to elevated carbon dioxide concentration [CO2] in the short-term (min) should be highly temperature dependent at high photon flux. However, it is unclear if long-term (days, weeks) adaptation to a given growth temperature alters the temperature-dependent stimulation of photosynthesis to [CO2]. In velveltleaf (Albutilon theophrasti), the response of photosynthesis, determined as CO2 assimilation, was measured over a range of internal CO2 concentrations at 7 short-term measurement (12, 16, 20, 24, 28, 32, 36 degrees C) temperatures for each of 4 long-term growth (16, 20, 28 and 32 degrees C) temperatures. In vivo estimates of VCmax, the maximum RuBP saturated rate of carboxylation, and Jmax, the light-saturated rate of potential electron transport, were determined from gas exchange measurements for each temperature combination. Overall, previous exposure to a given growth temperature adjusted the optimal temperatures of Jmax and VCmax with subsequently greater enhancement of photosynthesis at elevated [CO2] (i.e., a greater enhancement of photosynthesis at elevated [CO2] was observed at low measurement temperatures for A. theophrasti grown at low growth temperatures compared with higher growth temperatures, and vice versa for plants grown and measured at high temperatures). Previous biochemical based models used to predict the interaction between rising [CO2] and temperature on photosynthesis have generally assumed no growth temperature effect on carboxylation kinetics or no limitation by Jmax. In the current study, these models over predicted the temperature dependence of the photosynthetic response to elevated [CO2] at temperatures above 24 degrees C. If these models are modified to include long-term adjustments of Jmax and VCmax to growth temperature, then greater agreement between observed and predicted values was obtained.     

The rate-limiting step for CO(2) assimilation at different temperatures is influenced by the leaf nitrogen content in several C(3) crop species

Effects of nitrogen (N) supply on the limiting step of CO(2) assimilation rate (A) at 380 μmol mol(-1) CO(2) concentration (A(380) ) at several leaf temperatures were studied in several crops, since N nutrition alters N allocation between photosynthetic components. Contents of leaf N, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) increased with increasing N supply, but the cyt f/Rubisco ratio decreased. Large leaf N content was linked to a high stomatal (g(s) ) and mesophyll conductance (g(m) ), but resulted in a lower intercellular (C(i) ) and chloroplast CO(2) concentration (C(c) ) because the increase in g(s) and g(m) was insufficient to compensate for change in A(380) . The A-C(c) response was used to estimate the maximum rate of RuBP carboxylation (V(cmax) ) and chloroplast electron transport (J(max) ). The J(max) /V(cmax) ratio decreased with reductions in leaf N content, which was consistent with the results of the cyt f/Rubisco ratio. Analysis using the C(3) photosynthesis model indicated that A(380) tended to be limited by RuBP carboxylation in plants grown at low N concentration, whereas it was limited by RuBP regeneration in plants grown at high N concentration. We conclude that the limiting step of A(380) depends on leaf N content and is mainly determined by N partitioning between Rubisco and electron transport components.     

Response of superoxide dismutase isoenzymes in tomato plants (Lycopersicon esculentum) during thermo-acclimation of the photosynthetic apparatus

Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25 degrees C and 8 h dark at 20 degrees C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35 degrees C for 4 h in dark for 3 days), dark treatment (plants exposed to 25 degrees C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45 degrees C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45 degrees C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45 degrees C) was imposed. In these plants, the CO(2) assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (V(cmax)) and maximum electron transport rate contributing to Rubisco regeneration (J(max)). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO(2) assimilation rate and also in the values of V(cmax) and J(max). Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (F(m)) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the F(m) values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35 degrees C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of V(cmax) and J(max). Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes.     

Temperature response of photosynthesis and internal conductance to CO2: results from two independent approaches

The internal conductance to CO(2) transfer from intercellular spaces to chloroplasts poses a major limitation to photosynthesis, but few studies have investigated its temperature response. The aim of this study was to determine the temperature response of photosynthesis and internal conductance between 10 degrees C and 35 degrees C in seedlings of a deciduous forest tree species, Quercus canariensis. Internal conductance was estimated via simultaneous measurements of gas exchange and chlorophyll fluorescence ("variable J method"). Two of the required parameters, the intercellular photocompensation point (C(i)*) and rate of mitochondrial respiration in the light (R(d)), were estimated by the Laisk method. These were used to calculate the chloroplastic photocompensation point (Gamma*) in a simultaneous equation with g(i). An independent estimate of internal conductance was obtained by a novel curve-fitting method based on the curvature of the initial Rubisco-limited portion of an A/C(i) curve. The temperature responses of the rate of Rubisco carboxylation (V(cmax)) and the RuBP limited rate of electron transport (J(max)) were determined from chloroplastic CO(2) concentrations. The rate of net photosynthesis peaked at 24 degrees C. C(i)* was similar to reports for other species with a C(i)* of 39 micromol mol(-1) at 25 degrees C and an activation energy of 34 kJ mol(-1). Gamma* was very similar to the published temperature response for Spinacia oleracea from 20 degrees C to 35 degrees C, but was slightly greater at 10 degrees C and 15 degrees C. J(max) peaked at 30 degrees C, whereas V(cmax) did not reach a maximum between 10 degrees C and 35 degrees C. Activation energies were 49 kJ mol(-1) for V(cmax) and 100 kJ mol(-1) for J(max). Both methods showed that internal conductance doubled from 10 degrees C to 20 degrees C, and then was nearly temperature-independent from 20 degrees C to 35 degrees C. Hence, the temperature response of internal conductance could not be fitted to an Arrhenius function. The best fit to estimated g(i) was obtained with a three-parameter log normal function (R(2)=0.98), with a maximum g(i) of 0.19 mol m(-2) s(-1) at 29 degrees C.     

Low temperature effects on photosynthesis and growth of grapevine

Growth and photosynthesis of grapevine (Vitis vinifera L.) planted on two sloping cool climate vineyards were measured during the early growth season. At both vineyards, a small difference in mean minimum air temperature (1–3 °C) between two microsites accumulated over time, producing differences in shoot growth rate. The growth rates of the warmer (upper) microsite were 34–63% higher than the cooler (lower) site. Photosynthesis measurements of both east and west canopy sides revealed that the difference in carbon gain between the warmer and cooler microsites was due to low temperatures restricting the photosynthetic contribution of east‐facing leaves. East‐facing leaves at the warmer microsite experienced less time at suboptimal temperature while being exposed to high irradiance, contributing to an average 10% greater net carbon gain compared to the east‐facing leaves at the cooler microsite. This chilling‐induced reduction in photosynthesis was not due to net photo‐inhibition. Further analysis revealed that CO₂‐ and light‐saturated photosynthesis of grapevines was restricted by stomatal closure from 15 to 25 °C and by a limitation of RuBP regeneration and/or end‐product limitation from 5 to 15 °C. Changes in photosynthetic carboxylation efficiency implied that Rubisco activity may also play a regulatory role at all temperatures. This restriction of total photosynthetic carbon gain is proposed to be a major contributor to the temperature dependence of growth rate at both vineyards during the early season growth period.     

Temperature dependence of two parameters in a photosynthesis model

The temperature dependence of the photosynthetic parameters V_cmax, the maximum catalytic rate of the enzyme Rubisco, and J_max, the maximum electron transport rate, were examined using published datasets. An Arrehenius equation, modified to account for decreases in each parameter at high temperatures, satisfactorily described the temperature response for both parameters. There was remarkable conformity in V_cmax and J_max between all plants at T_leaf < 25 °C, when each parameter was normalized by their respective values at 25 °C (V_cmax0 and J_max0), but showed a high degree of variability between and within species at T_leaf > 30 °C. For both normalized V_cmax and J_max, the maximum fractional error introduced by assuming a common temperature response function is < ± 0·1 for most plants and < ± 0·22 for all plants when T_leaf < 25 °C. Fractional errors are typically < ± 0·45 in the temperature range 25–30 °C, but very large errors occur when a common function is used to estimate the photosynthetic parameters at temperatures > 30 °C. The ratio J_max/V_cmax varies with temperature, but analysis of the ratio at T_leaf = 25 °C using the fitted mean temperature response functions results in J_max0/V_cmax0 = 2·00 ± 0·60 (SD, n = 43).     

Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes

Air temperatures have risen over the past 50 yr along the Antarctic Peninsula, and it is unclear what impact this is having on Antarctic plants. We examined the growth response of the Antarctic vascular plants Colobanthus quitensis (Caryophyllaceae) and Deschampsia antarctica (Poaceae) to temperature and also assessed their ability for thermal acclimation, in terms of whole-canopy net photosynthesis (P(n)) and dark respiration (R(d)), by growing plants for 90 d under three contrasting temperature regimes: 7°C day/7°C night, 12°C day/7°C night, and 20°C day/7°C night (18 h/6 h). These daytime temperatures represent suboptimal (7°C), near-optimal (12°C), and supraoptimal (20°C) temperatures for P(n) based on field measurements at the collection site near Palmer Station along the west coast of the Antarctic Peninsula. Plants of both species grown at a daytime temperature of 20°C had greater RGR (relative growth rate) and produced 2.2-3.3 times as much total biomass as plants grown at daytime temperatures of 12° or 7°C. Plants grown at 20°C also produced 2.0-4.1 times as many leaves, 3.4-5.5 times as much total leaf area, and had 1.5-1.6 times the LAR (leaf area ratio; leaf area:total biomass) and 1.1-1.4 times the LMR (leaf mass ratio; leaf mass:total biomass) of plants grown at 12° or 7°C. Greater RGR and biomass production at 20°C appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of P(n) (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12°C, and rates of plants grown at 20°C were only 58 (C. quitensis) or 64% (D. antarctica) of the rates in plants grown at 12°C. Thus, lower P(n) per leaf area in plants grown at 20°C was more than offset by much greater leaf-area production. Rates of whole-canopy P(n) (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20°C, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of P(n) (leaf-area basis) as the optimal temperature for P(n) increased from 8.4° to 10.3° to 11.5°C as daytime growth temperatures increased from 7° to 12° to 20°C. There was no evidence for relative acclimation of P(n) in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10°C) for P(n). There was no evidence for absolute acclimation of P(n) in either species, as rates of P(n) in plants grown at a daytime temperature of 12°C were higher than those of plants grown at daytime temperatures of 7° or 20°C, when measured at their respective growth temperatures. The poor ability for photosynthetic acclimation in these species may be associated with the relatively stable maritime temperature regime during the growing season along the Peninsula. In contrast to P(n), both species exhibited full acclimation of R(d), and rates of R(d) on a leaf-area basis were similar among treatments when measured at their respective daytime growth temperature. Our results suggest that in the absence of interspecific competition, continued warming along the Peninsula will lead to improved vegetative growth of these species due to (1) greater biomass allocation to leaf-area production (as opposed to improved rates of P(n) per leaf area) and (2) their ability to acclimate R(d), such that respiratory losses per leaf area do not increase under higher temperature regimes.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: effect of growth temperature on photoinhibition and recovery

Intact leaves of kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) from plants grown in a range of controlled temperatures from 15/10 to 30/25°C were exposed to a photon flux density (PFD) of 1500 μmol·m⁻²·s⁻¹ at leaf temperatures between 10 and 25°C. Photoinhibition and recovery were followed at the same temperatures and at a PFD of 20 μmol·m⁻²·s⁻¹, by measuring chlorophyll fluorescence at 77 K and 692 nm, by measuring the photon yield of photosynthetic O₂ evolution and light-saturated net photosynthetic CO₂ uptake. The growth of plants at low temperatures resulted in chronic photoinhibition as evident from reduced fluorescence and photon yields. However, low-temperature-grown plants apparently had a higher capacity to dissipate excess excitation energy than leaves from plants grown at high temperatures. Induced photoinhibition, from exposure to a PFD above that during growth, was less severe in low-temperature-grown plants, particularly at high exposure temperatures. Net changes in the instantaneous fluorescence,F ₀, indicated that little or no photoinhibition occurred when low-temperature-grown plants were exposed to high-light at high temperatures. In contrast, high-temperature-grown plants were highly susceptible to photoinhibitory damage at all exposure temperatures. These data indicate acclimation in photosynthesis and changes in the capacity to dissipate excess excitation energy occurred in kiwifruit leaves with changes in growth temperature. Both processes contributed to changes in susceptibility to photoinhibition at the different growth temperatures. However, growth temperature also affected the capacity for recovery, with leaves from plants grown at low temperatures having moderate rates of recovery at low temperatures compared with leaves from plants grown at high temperatures which had negligible recovery. This also contributed to the reduced susceptibility to photoinhibition in low-temperature-grown plants. However, extreme photoinhibition resulted in severe reductions in the efficiency and capacity for photosynthesis.