Model Of C3 Photosynthesis Research Articles

Connecting detailed photosynthetic kinetics to crop growth and yield: a coupled modelling framework

Abstract Photosynthesis and crop growth are inseparable processes that govern plant carbon assimilation and allocation. An accurate model description of these processes can bridge dynamics at the leaf and canopy levels, assisting in identifying potential photosynthetic improvements that can be converted into increased yield. Integrating multiscale biophysical processes and achieving computational effectiveness for seasonal simulations, however, are challenging. Here, we present a fully coupled modelling framework that integrates a metabolic model of C3 photosynthesis (ePhotosynthesis) and a semi-mechanistic crop growth model (BioCro). We replaced the leaf-level Farquhar photosynthesis model in BioCro with the ePhotosynthesis model that mechanistically describes the photosystem electron transport processes and the C3 carbon metabolism including the Calvin–Benson–Bassham cycle and the photorespiratory pathway. The coupled BioCro-ePhotosynthesis model was calibrated to represent a soybean cultivar and developed to be operationally fast for seasonal simulations. As an example of model application, we conducted a global sensitivity analysis of 26 enzymes under an average daytime intercepted radiation of 400 µmol m−2 s−1, identifying 2 enzymes, phosphoglycerate kinase (PGK) and phosphoribulokinase (PRK), which had the largest impact on the leaf-level assimilation. Increasing PGK and PRK by 2-fold was predicted to increase the leaf-level assimilation by 8.3 % and the final seed yield by 6.75 % ± 0.5 % over 4 years of observed field climate data. The coupled BioCro-ePhotosynthesis model provides a seamless and efficient integration between the leaf-level metabolism and the field-level yield over a full growing season. The coupled model could be further applied to investigate non-steady-state photosynthetic processes such as non-photochemical quenching.

Improved representation of plant physiology in the JULES-vn5.6 land surface model: photosynthesis, stomatal conductance and thermal acclimation

Abstract. Carbon and water cycle dynamics of vegetation are controlled primarily by photosynthesis and stomatal conductance (gs). Our goal is to improve the representation of these key physiological processes within the JULES land surface model, with a particular focus on refining the temperature sensitivity of photosynthesis, impacting modelled carbon, energy and water fluxes. We test (1) an implementation of the Farquhar et al. (1980) photosynthesis scheme and associated plant functional type-dependent photosynthetic temperature response functions, (2) the optimality-based gs scheme from Medlyn et al. (2011) and (3) the Kattge and Knorr (2007) photosynthetic capacity thermal acclimation scheme. New parameters for each model configuration are adopted from recent large observational datasets that synthesise global experimental data. These developments to JULES incorporate current physiological understanding of vegetation behaviour into the model and enable users to derive direct links between model parameters and ongoing measurement campaigns that refine such parameter values. Replacement of the original Collatz et al. (1991) C3 photosynthesis model with the Farquhar scheme results in large changes in GPP for the current day, with ∼ 10 % reduction in seasonal (June–August, JJA, and December–February, DJF) mean GPP in tropical forests and ∼ 20 % increase in the northern high-latitude forests in JJA. The optimality-based gs model decreases the latent heat flux for the present day (∼ 10 %, with an associated increase in sensible heat flux) across regions dominated by needleleaf evergreen forest in the Northern Hemisphere summer. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme reduced tropical forest GPP by up to 5 % and increased GPP in the high-northern-latitude forests by between 2 % and 5 %. Evaluation of simulated carbon and water fluxes by each model configuration against global data products shows this latter configuration generates improvements in these key areas. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme improved modelled carbon fluxes in tropical and high-northern-latitude forests in JJA and improved the simulation of evapotranspiration across much of the Northern Hemisphere in JJA. Having established good model performance for the contemporary period, we force this new version of JULES offline with a future climate scenario corresponding to rising atmospheric greenhouse gases (Shared Socioeconomic Pathway (SSP5), Representative Concentration Pathway 8.5 (RCP8.5)). In particular, these calculations allow for understanding of the effects of long-term warming. We find that the impact of thermal acclimation coupled with the optimality-based gs model on simulated fluxes increases latent heat flux (+50 %) by the year 2050 compared to the JULES model configuration without acclimation. This new JULES configuration also projects increased GPP across tropical (+10 %) and northern-latitude regions (+30 %) by 2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based gs scheme together improve the simulation of carbon and water fluxes for the current day and have a large impact on modelled future carbon cycle dynamics in a warming world.

Optimality-based modelling of climate impacts on global potential wheat yield

Evaluation of potential crop yields is important for global food security assessment because it represents the biophysical ‘ceiling’ determined by variety, climate and ambient CO2. Statistical approaches have limitations when assessing future potential yields, while large differences between results obtained using process-based models reflect uncertainties in model parameterisations. Here we simulate the potential yield of wheat across the present-day wheat-growing areas, using a new global model that couples a parameter-sparse, optimality-based representation of gross primary production (GPP) to empirical functions relating GPP, biomass production and yield. The model reconciles the transparency and parsimony of statistical models with a mechanistic grounding in the standard model of C3 photosynthesis, and seamlessly integrates photosynthetic acclimation and CO2 fertilization effects. The model accurately predicted the CO2 response observed in FACE experiments, and captured the magnitude and spatial pattern of EARTHSTAT ‘attainable yield’ data in 2000 CE better than process-based models in ISIMIP. Global simulations of potential yield during 1981–2016 were analysed in parallel with global historical data on actual yield, in order to test the hypothesis that environmental effects on modelled potential yields would also be shown in observed actual yields. Higher temperatures are thereby shown to have negatively affected (potential and actual) yields over much of the world. Greater solar radiation is associated with higher yields in humid regions, but lower yields in semi-arid regions. Greater precipitation is associated with higher yields in semi-arid regions. The effect of rising CO2 is reflected in increasing actual yield, but trends in actual yield are stronger than the CO2 effect in many regions, presumably because they also include effects of crop breeding and improved management. We present this hybrid modelling approach as a useful addition to the toolkit for assessing global environmental change impacts on the growth and yield of arable crops.

Computational Analysis of Alternative Photosynthetic Electron Flows Linked With Oxidative Stress.

During photosynthesis, organisms respond to their energy demand and ensure the supply of energy and redox equivalents that sustain metabolism. Hence, the photosynthetic apparatus can, and in fact should, be treated as an integrated supply-demand system. Any imbalance in the energy produced and consumed can lead to adverse reactions, such as the production of reactive oxygen species (ROS). Reaction centres of both photosystems are known sites of ROS production. Here, we investigate in particular the central role of Photosystem I (PSI) in this tightly regulated system. Using a computational approach we have expanded a previously published mechanistic model of C3 photosynthesis by including ROS producing and scavenging reactions around PSI. These include two water to water reactions mediated by Plastid terminal oxidase (PTOX) and Mehler and the ascorbate-glutathione (ASC-GSH) cycle, as a main non-enzymatic antioxidant. We have used this model to predict flux distributions through alternative electron pathways under various environmental stress conditions by systematically varying light intensity and enzymatic activity of key reactions. In particular, we studied the link between ROS formation and activation of pathways around PSI as potential scavenging mechanisms. This work shines light on the role of alternative electron pathways in photosynthetic acclimation and investigates the effect of environmental perturbations on PSI activity in the context of metabolic productivity.

Temperature responses of photosynthesis and stomatal conductance in rice and wheat plants

The mechanisms for the different temperature (T) responses of leaf photosynthetic rate (A) and stomatal conductance (gs) have not been thoroughly elucidated, and the uncertainties and limitations facing the optimal-stomata models have not been systematically investigated. In the present study, the temperature responses of A, gs, and mesophyll conductance (gm) were studied in the selected rice and wheat genotypes, and the C3 photosynthesis model and three widely used optimal-stomata models were introduced to investigate these two questions. The photosynthetic limiting process varied significantly between rice and wheat plants. The photosynthetic limitation and gm had strong impacts on the temperature response of λ, the key parameter for the optimal-stomata models. λ was increased with T when photosynthesis was limited by the RuBP carboxylation, while it was decreased with T when it was limited by the RuBP regeneration. Because of the negative correlation between λ and gs, the differing λ-T relationships may explain the different gs-T relationships between the selected genotypes. This is the first study using the optimal-stomata models to interpret the differential gs-T relationships and highlights the importance of estimating gm and the photosynthetic limitations before applying the optimal-stomata models.

Oxygen response of leaf CO2 compensation points used to determine Rubisco specificity factors of gymnosperm species

Rubisco specificity factor (Sc/o), a measure of the relative capacities of an enzyme to catalyze carboxylation and oxygenation of ribulose-1,5-bisphosphate, determines the extent of photosynthetic CO2 assimilation and photorespiratory CO2 release. The current model of C3 photosynthesis, the Farquhar-von Caemmerer-Berry (FvCB) model, requires a species-specific Sc/o. However, Sc/o values have never been reported in conifers, likely because in vitro kinetic analysis of conifer Rubisco presents difficulties. To estimate the Sc/o of conifers and compare it with angiosperm Sc/o, we measured changes in leaf CO2 compensation points (Γ) in response to O2 partial pressure for a variety of leaves, with different rates of day respiration (Rday) and maximum Rubisco carboxylation (Vcmax) in gymnosperms (Ginkgo biloba), conifers (Metasequoia glyptostroboides and Cryptomeria japonica), and angiosperms (Nicotiana tabacum and Phaseolus vulgaris). As predicted by the FvCB model, the slope of a linear function of Γ vs O2 partial pressure, d, increased alongside increasing Rday/Vcmax. The Sc/o was obtainable from this relationship between d and Rday/Vcmax, because the d values at Rday/Vcmax = 0 corresponded to α/Sc/o, where α was the photorespiratory CO2 release rate per Rubisco oxygenation rate (generally assumed to be 0.5). The calculated Sc/o values of N. tabacum and P. vulgaris exhibited good agreement with those reported by in vitro studies. The Sc/o values of both conifers were similar to those of the two angiosperm species. In contrast, the Sc/o value of G. biloba was significantly lower than those of the other four studied species. These results suggest that our new method for Sc/o estimation is applicable to C3 plants, including those for which in vitro kinetic analysis is difficult. Furthermore, results also suggest that conifer Sc/o does not differ significantly from that of C3 angiosperms, assuming α remains unchanged.

No evidence for triose phosphate limitation of light-saturated leaf photosynthesis under current atmospheric CO2 concentration.

The triose phosphate utilization (TPU) rate has been identified as one of the processes that can limit terrestrial plant photosynthesis. However, we lack a robust quantitative assessment of TPU limitation of photosynthesis at the global scale. As a result, TPU, and its potential limitation of photosynthesis, is poorly represented in terrestrial biosphere models (TBMs). In this study, we utilized a global data set of photosynthetic CO2 response curves representing 141 species from tropical rainforests to Arctic tundra. We quantified TPU by fitting the standard biochemical model of C3 photosynthesis to measured photosynthetic CO2 response curves and characterized its instantaneous temperature response. Our results demonstrate that TPU does not limit leaf photosynthesis at the current ambient atmospheric CO2 concentration. Furthermore, our results showed that the light-saturated photosynthetic rates of plants growing in cold environments are not more often limited by TPU than those of plants growing in warmer environments. In addition, our study showed that the instantaneous temperature response of TPU is distinct from temperature response of the maximum rate of Rubisco carboxylation. The new formulations of the temperature response of TPU derived in this study may prove useful in quantifying the biochemical limits to terrestrial plant photosynthesis and improve the representation of plant photosynthesis in TBMs.

The multi-assumption architecture and testbed (MAAT v1.0): R code for generating ensembles with dynamic model structure and analysis of epistemic uncertainty from multiple sources

Abstract. Computer models are ubiquitous tools used to represent systems across many scientific and engineering domains. For any given system, many computer models exist, each built on different assumptions and demonstrating variability in the ways in which these systems can be represented. This variability is known as epistemic uncertainty, i.e. uncertainty in our knowledge of how these systems operate. Two primary sources of epistemic uncertainty are (1) uncertain parameter values and (2) uncertain mathematical representations of the processes that comprise the system. Many formal methods exist to analyse parameter-based epistemic uncertainty, while process-representation-based epistemic uncertainty is often analysed post hoc, incompletely, informally, or is ignored. In this model description paper we present the multi-assumption architecture and testbed (MAAT v1.0) designed to formally and completely analyse process-representation-based epistemic uncertainty. MAAT is a modular modelling code that can simply and efficiently vary model structure (process representation), allowing for the generation and running of large model ensembles that vary in process representation, parameters, parameter values, and environmental conditions during a single execution of the code. MAAT v1.0 approaches epistemic uncertainty through sensitivity analysis, assigning variability in model output to processes (process representation and parameters) or to individual parameters. In this model description paper we describe MAAT and, by using a simple groundwater model example, verify that the sensitivity analysis algorithms have been correctly implemented. The main system model currently coded in MAAT is a unified, leaf-scale enzyme kinetic model of C3 photosynthesis. In the Appendix we describe the photosynthesis model and the unification of multiple representations of photosynthetic processes. The numerical solution to leaf-scale photosynthesis is verified and examples of process variability in temperature response functions are provided. For rapid application to new systems, the MAAT algorithms for efficient variation of model structure and sensitivity analysis are agnostic of the specific system model employed. Therefore MAAT provides a tool for the development of novel or toy models in many domains, i.e. not only photosynthesis, facilitating rapid informal and formal comparison of alternative modelling approaches.

Do all leaf photosynthesis parameters of rice acclimate to elevated CO2, elevated temperature, and their combination, in FACE environments?

Leaf photosynthesis of crops acclimates to elevated CO2 and temperature, but studies quantifying responses of leaf photosynthetic parameters to combined CO2 and temperature increases under field conditions are scarce. We measured leaf photosynthesis of rice cultivars Changyou 5 and Nanjing 9108 grown in two free-air CO2 enrichment (FACE) systems, respectively, installed in paddy fields. Each FACE system had four combinations of two levels of CO2 (ambient and enriched) and two levels of canopy temperature (no warming and warmed by 1.0-2.0°C). Parameters of the C3 photosynthesis model of Farquhar, von Caemmerer and Berry (the FvCB model), and of a stomatal conductance (gs ) model were estimated for the four conditions. Most photosynthetic parameters acclimated to elevated CO2 , elevated temperature, and their combination. The combination of elevated CO2 and temperature changed the functional relationships between biochemical parameters and leaf nitrogen content for Changyou 5. The gs model significantly underestimated gs under the combination of elevated CO2 and temperature by 19% for Changyou 5 and by 10% for Nanjing 9108 if no acclimation was assumed. However, our further analysis applying the coupled gs -FvCB model to an independent, previously published FACE experiment showed that including such an acclimation response of gs hardly improved prediction of leaf photosynthesis under the four combinations of CO2 and temperature. Therefore, the typical procedure that crop models using the FvCB and gs models are parameterized from plants grown under current ambient conditions may not result in critical errors in projecting productivity of paddy rice under future global change.

Biochemical model of C3 photosynthesis applied to wheat at different temperatures.

We examined the effects of leaf temperature on the estimation of maximal Rubisco capacity (Vcmax ) from gas exchange measurements of wheat leaves using a C3 photosynthesis model. Cultivars of spring wheat (Triticum aestivum (L)) and triticale (X Triticosecale Wittmack) were grown in a greenhouse or in the field and measured at a range of temperatures under controlled conditions in a growth cabinet (2 and 21% O2 ) or in the field using natural diurnal variation in temperature, respectively. Published Rubisco kinetic constants for tobacco did not describe the observed CO2 response curves well as temperature varied. By assuming values for the Rubisco Michaelis-Menten constants for CO2 (Kc ) and O2 (Ko ) at 25°C derived from tobacco and the activation energies of Vcmax from wheat and respiration in the light, Rd , from tobacco, we derived activation energies for Kc and Ko (93.7 and 33.6kJ mol-1 , respectively) that considerably improved the fit of the model to observed data. We confirmed that temperature dependence of dark respiration for wheat was well described by the activation energy for Rd from tobacco. The new parameters improved the estimation of Vcmax under field conditions, where temperatures increased through the day.

The sensitivity of photosynthesis to O2 and CO2 concentration identifies strong Rubisco control above the thermal optimum

The biochemical model of C3 photosynthesis by Farquhar, von Caemmerer and Berry (FvCB) assumes that photosynthetic CO2 assimilation is limited by one of three biochemical processes that are not always easily discerned. This leads to improper assessments of biochemical limitations that limit the accuracy of the model predictions. We use the sensitivity of rates of CO2 assimilation and photosynthetic electron transport to changes in O2 and CO2 concentration in the chloroplast to evaluate photosynthetic limitations. Assessing the sensitivities to O2 and CO2 concentrations reduces the impact of uncertainties in the fixed parameters to a minimum and simultaneously entirely eliminates the need to determine the variable parameters of the model, such as Vcmax , J, or TP . Our analyses demonstrate that Rubisco limits carbon assimilation at high temperatures, while it is limited by triose phosphate utilization at lower temperatures and at higher CO2 concentrations. Measurements can be assigned a priori to one of the three functions of the FvCB model, allowing testing for the suitability of the selected fixed parameters of the model. This approach can improve the reliability of photosynthesis models on scales from the leaf level to estimating the global carbon budget.

Photorespiration plays an important role in the regulation of photosynthetic electron flow under fluctuating light in tobacco plants grown under full sunlight.

Plants usually experience dynamic fluctuations of light intensities under natural conditions. However, the responses of mesophyll conductance, CO2 assimilation, and photorespiration to light fluctuation are not well understood. To address this question, we measured photosynthetic parameters of gas exchange and chlorophyll fluorescence in tobacco leaves at 2-min intervals while irradiance levels alternated between 100 and 1200 μmol photons m−2 s−1. Compared with leaves exposed to a constant light of 1200 μmol photons m−2 s−1, both stomatal and mesophyll conductances were significantly restricted in leaves treated with fluctuating light condition. Meanwhile, CO2 assimilation rate and electron flow devoted to RuBP carboxylation at 1200 μmol photons m−2 s−1 under fluctuating light were limited by the low chloroplast CO2 concentration. Analysis based on the C3 photosynthesis model indicated that, at 1200 μmol photons m−2 s−1 under fluctuating light, the CO2 assimilation rate was limited by RuBP carboxylation. Electron flow devoted to RuBP oxygenation at 1200 μmol photons m−2 s−1 under fluctuating light remained at nearly the maximum level throughout the experimental period. We conclude that fluctuating light restricts CO2 assimilation by decreasing both stomatal and mesophyll conductances. Under such conditions, photorespiration plays an important role in the regulation of photosynthetic electron flow.

Modelling C3 photosynthesis from the chloroplast to the ecosystem

AbstractGlobally, photosynthesis accounts for the largest flux of CO2 from the atmosphere into ecosystems and is the driving process for terrestrial ecosystem function. The importance of accurate predictions of photosynthesis over a range of plant growth conditions led to the development of a C3 photosynthesis model by Farquhar, von Caemmerer & Berry that has become increasingly important as society places greater pressures on vegetation. The photosynthesis model has played a major role in defining the path towards scientific understanding of photosynthetic carbon uptake and the role of photosynthesis on regulating the earth's climate and biogeochemical systems. In this review, we summarize the photosynthesis model, including its continued development and applications. We also review the implications these developments have on quantifying photosynthesis at a wide range of spatial and temporal scales, and discuss the model's role in determining photosynthetic responses to changes in environmental conditions. Finally, the review includes a discussion of the larger‐scale modelling and remote‐sensing applications that rely on the leaf photosynthesis model and are likely to open new scientific avenues to address the increasing challenges to plant productivity over the next century.

Leaf gas-exchange characteristics of four Japanese and four Dutch tomato cultivars grown in a greenhouse

Modern Dutch tomato cultivars reportedly yield 1.2–1.6 times as much fresh fruit as Japanese cultivars. To analyze a factor potentially contributing to the yield difference, leaf gas-exchange characteristics were determined for four Japanese (‘Asabiyori 10’, ‘Momotaro York’, ‘Reiyo’ and ‘Renaissance’) and four Dutch (‘Dundee’, ‘Levanzo’, ‘Tomimaru Mucho’ and ‘Vinchy’) tomato cultivars and evaluated according to a C3 photosynthesis model. Plants were grown hydroponically with a high-wire system in a glass greenhouse, and leaf gas-exchange rates were measured at different photosynthetic photon flux and CO2 partial pressures with 130- to 140-d-old plants. Overall, Dutch cultivars generally had higher photosynthetic capacity than Japanese cultivars both under the light-limited and -saturated conditions, and both under the CO2-limited and -saturated conditions; thus, both capacities of ribulose-1,5-bisphosphate (RuBP) carboxylation and regeneration were relatively higher in Dutch cultivars. However, not all Dutch cultivars were superior than Japanese cultivars in terms of photosynthesis: although Dutch cultivars ‘Levanzo’ and ‘Tomimaru Mucho’ tended to have higher leaf photosynthetic capacity than Japanese cultivars ‘Asabiyori 10’ and ‘Renaissance’, Japanese cultivars ‘Momotaro York’ and ‘Reiyo’ and Dutch cultivars ‘Dundee’ and ‘Vinchy’ possessed comparable photosynthetic capacity. Thus, there is variation of photosynthetic capacity even within Dutch cultivars and within Japanese cultivars.

Optimal crop canopy architecture to maximise canopy photosynthetic CO2 uptake under elevated CO2 - a theoretical study using a mechanistic model of canopy photosynthesis.

Canopy architecture has been a major target in crop breeding for improved yields. Whether crop architectures in current elite crop cultivars can be modified for increased canopy CO2 uptake rate (Ac) under elevated atmospheric CO2 concentrations (Ca) is currently unknown. To study this question, we developed a new model of canopy photosynthesis, which includes three components: (i) a canopy architectural model; (ii) a forward ray tracing algorithm; and (iii) a steady-state biochemical model of C3 photosynthesis. With this model, we demonstrated that the Ac estimated from 'average' canopy light conditions is ~25% higher than that from light conditions at individual points in the canopy. We also evaluated theoretically the influence of canopy architectural on Ac under current and future Ca in rice. Simulation results suggest that to gain an optimal Ac for the examined rice cultivar, the stem height, leaf width and leaf angles can be manipulated to enhance canopy photosynthesis. This model provides a framework for designing ideal crop architectures to gain optimal Ac under future changing climate conditions. A close linkage between canopy photosynthesis modelling and canopy photosynthesis measurements is required to fully realise the potential of such modelling approaches in guiding crop improvements.

E‐photosynthesis: a comprehensive dynamic mechanistic model of C3 photosynthesis: from light capture to sucrose synthesis

Photosynthesis is arguably the most researched of all plant processes. A dynamic model of leaf photosynthesis that includes each discrete process from light capture to carbohydrate synthesis, e-photosynthesis, is described. It was developed by linking and extending our previous models of photosystem II (PSII) energy transfer and photosynthetic C3 carbon metabolism to include electron transfer processes around photosystem I (PSI), ion transfer between the lumen and stroma, ATP synthesis and NADP reduction to provide a complete representation. Different regulatory processes linking the light and dark reactions are also included: Rubisco activation via Rubisco activase, pH and xanthophyll cycle-dependent non-photochemical quenching mechanisms, as well as the regulation of enzyme activities via the ferredoxin-theoredoxin system. Although many further feedback and feedforward controls undoubtedly exist, it is shown that e-photosynthesis effectively mimics the typical kinetics of leaf CO₂ uptake, O₂ evolution, chlorophyll fluorescence emission, lumen and stromal pH, and membrane potential following perturbations in light, [CO₂] and [O₂] observed in intact C3 leaves. The model provides a framework for guiding engineering of improved photosynthetic efficiency, for evaluating multiple non-invasive measures used in emerging phenomics facilities, and for quantitative assessment of strengths and weaknesses within the understanding of photosynthesis as an integrated process.

Photosynthesis in silico. Understanding complexity from molecules to ecosystems

Photosynthesis in silico. Understanding complexity from molecules to ecosystems

Phenotypic Plasticity in Photosynthetic Temperature Acclimation among Crop Species with Different Cold Tolerances

While interspecific variation in the temperature response of photosynthesis is well documented, the underlying physiological mechanisms remain unknown. Moreover, mechanisms related to species-dependent differences in photosynthetic temperature acclimation are unclear. We compared photosynthetic temperature acclimation in 11 crop species differing in their cold tolerance, which were grown at 15 degrees C or 30 degrees C. Cold-tolerant species exhibited a large decrease in optimum temperature for the photosynthetic rate at 360 microL L(-1) CO(2) concentration [Opt (A(360))] when growth temperature decreased from 30 degrees C to 15 degrees C, whereas cold-sensitive species were less plastic in Opt (A(360)). Analysis using the C(3) photosynthesis model shows that the limiting step of A(360) at the optimum temperature differed between cold-tolerant and cold-sensitive species; ribulose 1,5-bisphosphate carboxylation rate was limiting in cold-tolerant species, while ribulose 1,5-bisphosphate regeneration rate was limiting in cold-sensitive species. Alterations in parameters related to photosynthetic temperature acclimation, including the limiting step of A(360), leaf nitrogen, and Rubisco contents, were more plastic to growth temperature in cold-tolerant species than in cold-sensitive species. These plastic alterations contributed to the noted growth temperature-dependent changes in Opt (A(360)) in cold-tolerant species. Consequently, cold-tolerant species were able to maintain high A(360) at 15 degrees C or 30 degrees C, whereas cold-sensitive species were not. We conclude that differences in the plasticity of photosynthetic parameters with respect to growth temperature were responsible for the noted interspecific differences in photosynthetic temperature acclimation between cold-tolerant and cold-sensitive species.

Quantifying photosynthetic capacity and its relationship to leaf nitrogen content for global‐scale terrestrial biosphere models

AbstractPhotosynthetic capacity and its relationship to leaf nitrogen content are two of the most sensitive parameters of terrestrial biosphere models (TBM) whose representation in global‐scale simulations has been severely hampered by a lack of systematic analyses using a sufficiently broad database. Here, we use data of qualitative traits, climate and soil to subdivide the terrestrial vegetation into functional types (PFT), and then assimilate observations of carboxylation capacity, Vmax (723 data points), and maximum photosynthesis rates, Amax (776 data points), into the C3 photosynthesis model proposed by Farquhar et al. to constrain the relationship of (Vmax normalised to 25 °C) to leaf nitrogen content per unit leaf area for each PFT. In a second step, the resulting functions are used to predict per PFT from easily measurable values of leaf nitrogen content in natural vegetation (1966 data points). Mean values of thus obtained are implemented into a TBM (BETHY within the coupled climate–vegetation model ECHAM5/JSBACH) and modelled gross primary production (GPP) is compared with independent observations on stand scale. Apart from providing parameter ranges per PFT constrained from much more comprehensive data, the results of this analysis enable several major improvements on previous parameterisations. (1) The range of mean between PFTs is dominated by differences of photosynthetic nitrogen use efficiency (NUE, defined as divided by leaf nitrogen content), while within each PFT, the scatter of values is dominated by the high variability of leaf nitrogen content. (2) We find a systematic depression of NUE on certain tropical soils that are known to be deficient in phosphorous. (3) of tropical trees derived by this study is substantially lower than earlier estimates currently used in TBMs, with an obvious effect on modelled GPP and surface temperature. (4) The root‐mean‐squared difference between modelled and observed GPP is substantially reduced.

The Role of Electron Transport in Determining the Temperature Dependence of the Photosynthetic Rate in Spinach Leaves Grown at Contrasting Temperatures

The temperature response of the uncoupled whole-chain electron transport rate (ETR) in thylakoid membranes differs depending on the growth temperature. However, the steps that limit whole-chain ETR are still unclear and the question of whether the temperature dependence of whole-chain ETR reflects that of the photosynthetic rate remains unresolved. Here, we determined the whole-chain, PSI and PSII ETR in thylakoid membranes isolated from spinach leaves grown at 30 degrees C [high temperature (HT)] and 15 degrees C [low temperature (LT)]. We measured temperature dependencies of the light-saturated photosynthetic rate at 360 microl l(-1) CO2 (A360) in HT and LT leaves. Both of the temperature dependences of whole-chain ETR and of A360 were different depending on the growth temperature. Whole-chain ETR was less than the rates of PSI ETR and PSII ETR in the broad temperature range, indicating that the process was limited by diffusion processes between the PSI and PSII. However, at high temperatures, whole-chain ETR appeared to be limited by not only the diffusion processes but also PSII ETR. The C3 photosynthesis model was used to evaluate the limitations of A360 by whole-chain ETR (Pr) and ribulose bisphosphate carboxylation (Pc). In HT leaves, A360 was co-limited by Pc and Pr at low temperatures, whereas at high temperatures, A360 was limited by Pc. On the other hand, in LT leaves, A360 was solely limited by Pc over the entire temperature range. The optimum temperature for A360 was determined by Pc in both HT and LT leaves. Thus, this study showed that, at low temperatures, the limiting step of A360 was different depending on the growth temperature, but was limited by Pc at high temperatures regardless of the growth temperatures.