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1.
The aims of this paper was to modify the photosynthesis model of Farquhar, von Caemmerer and Berry (FvCB) to be able to predict light dependency of the carboxylation capacity (Vc) and to improve the prediction of temperature dependency of the maximum carboxylation capacity (Vcmax) and the maximum electron transport rate (Jmax). The FvCB model was modified by adding a sub-model for Ribulose-1,5-bisphosphate carboxylase (Rubisco) activation and validating the parameters for temperature dependency of Vcmax and Jmax. Values of parameters for temperature dependency of Vcmax and Jmax were validated and adjusted based on data of the photosynthesis response to temperature. Parameter estimation was based on measurements under a wide range of environmental conditions, providing parameters with broad validity. The simultaneous estimation method and the nonlinear mixed effects model were applied to ensure the accuracy of the parameter estimation. The FvCB parameters, Vcmax, Jmax, α (the efficiency of light energy conversion), θ (the curvature of light response of electron transport), and Rd (the non-photorespiratory CO2 release) were estimated and validated on a dataset from two other years. Observations and predictions matched well (R2 = 0.94). We conclude that incorporating a sub-model of Rubisco activation improved the FvCB model through predicting light dependency of carboxylation rate; and that estimating Vcmax, Jmax, α, θ, and Rd requires data sets of both CO2 and light response curves.  相似文献   

2.
Chen CP  Zhu XG  Long SP 《Plant physiology》2008,148(2):1139-1147
Application of the widely used Farquhar model of photosynthesis in interpretation of gas exchange data assumes that photosynthetic properties are homogeneous throughout the leaf. Previous studies showed that heterogeneity in stomatal conductance (gs) across a leaf could affect the shape of the measured leaf photosynthetic CO2 uptake rate (A) versus intercellular CO2 concentration (Ci) response curve and, in turn, estimation of the critical biochemical parameters of this model. These are the maximum rates of carboxylation (Vc,max), whole-chain electron transport (Jmax), and triose-P utilization (VTPU). The effects of spatial variation in Vc,max, Jmax, and VTPU on estimation of leaf averages of these parameters from A-Ci curves measured on a whole leaf have not been investigated. A mathematical model incorporating defined degrees of spatial variability in Vc,max and Jmax was constructed. One hundred and ten theoretical leaves were simulated, each with the same average Vc,max and Jmax, but different coefficients of variation of the mean (CVVJ) and varying correlation between Vc,max and Jmax (Ω). Additionally, the interaction of variation in Vc,max and Jmax with heterogeneity in VTPU, gs, and light gradients within the leaf was also investigated. Transition from Vc,max- to Jmax-limited photosynthesis in the A-Ci curve was smooth in the most heterogeneous leaves, in contrast to a distinct inflection in the absence of heterogeneity. Spatial variability had little effect on the accuracy of estimation of Vc,max and Jmax from A-Ci curves when the two varied in concert (Ω = 1.0), but resulted in underestimation of both parameters when they varied independently (up to 12.5% in Vc,max and 17.7% in Jmax at CVVJ = 50%; Ω = 0.3). Heterogeneity in VTPU also significantly affected parameter estimates, but effects of heterogeneity in gs or light gradients were comparatively small. If Vc,max and Jmax derived from such heterogeneous leaves are used in models to project leaf photosynthesis, actual A is overestimated by up to 12% at the transition between Vc,max- and Jmax-limited photosynthesis. This could have implications for both crop production and Earth system models, including projections of the effects of atmospheric change.  相似文献   

3.
The effects of elevated atmospheric CO2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (Amax), the potential electron transport rate (Jmax), the maximum Rubisco activity (Vcmax) and leaf nitrogen concentration on mass (Nm) and area (Na) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO2]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO2]. Tables of model parameter values for different European forest species are given.  相似文献   

4.
Great uncertainty exists in the global exchange of carbon between the atmosphere and the terrestrial biosphere. An important source of this uncertainty lies in the dependency of photosynthesis on the maximum rate of carboxylation (Vcmax) and the maximum rate of electron transport (Jmax). Understanding and making accurate prediction of C fluxes thus requires accurate characterization of these rates and their relationship with plant nutrient status over large geographic scales. Plant nutrient status is indicated by the traits: leaf nitrogen (N), leaf phosphorus (P), and specific leaf area (SLA). Correlations between Vcmax and Jmax and leaf nitrogen (N) are typically derived from local to global scales, while correlations with leaf phosphorus (P) and specific leaf area (SLA) have typically been derived at a local scale. Thus, there is no global-scale relationship between Vcmax and Jmax and P or SLA limiting the ability of global-scale carbon flux models do not account for P or SLA. We gathered published data from 24 studies to reveal global relationships of Vcmax and Jmax with leaf N, P, and SLA. Vcmax was strongly related to leaf N, and increasing leaf P substantially increased the sensitivity of Vcmax to leaf N. Jmax was strongly related to Vcmax, and neither leaf N, P, or SLA had a substantial impact on the relationship. Although more data are needed to expand the applicability of the relationship, we show leaf P is a globally important determinant of photosynthetic rates. In a model of photosynthesis, we showed that at high leaf N (3 gm−2), increasing leaf P from 0.05 to 0.22 gm−2 nearly doubled assimilation rates. Finally, we show that plants may employ a conservative strategy of Jmax to Vcmax coordination that restricts photoinhibition when carboxylation is limiting at the expense of maximizing photosynthetic rates when light is limiting.  相似文献   

5.
To study the effects of different periods of ozone (O3) fumigation on photosynthesis in leaves of the Monarch birch (Betula maximowicziana), we undertook free air O3 fumigation to Monarch birch seedlings at a concentration of 60 nmol mol?1 during daytime. Plants were exposed to O3 at early, late or both periods in the growing season. The light-saturated net photosynthetic rate (A sat) in July and August was reduced by O3 exposure through a reduction in the maximum rate of carboxylation (V c,max). In early September, on the other hand, despite a reduction in V c,max, A sat was not reduced by O3 due to a counteracting increase in the stomatal conductance. Through the experiment, there was no difference in sensitivity to O3 between maturing and matured leaves. We analyzed the relationship between A sat, V c,max and accumulated stomatal O3 flux (AFst). Whereas V c,max decreased with increasing AFst, the correlation between A sat and AFst was weak because the response of stomatal conductance to O3 was affected by season. We conclude photosynthetic response of Monarch birch to O3 exposure changes with season. This is due to the inconstant stomatal response to O3 but not due to the respose of biochemical assimilation capacity in chloroplasts.  相似文献   

6.
Ku SB  Edwards GE 《Plant physiology》1977,59(5):991-999
The response of whole leaf photosynthesis of wheat (Triticum aestivum L.) in relation to soluble CO2 available to the mesophyll cells, under low (1.5%) O2 at 25, 30, and 35 C, followed Michaelis-Menten kinetics up to saturating CO2 but deviated at high CO2 levels where the experimental Vmax is considerably less than the calculated Vmax. The affinity of the leaves for CO2 during photosynthesis was similar from 25 to 35 C with Km (CO2) values of approximately 3.5 to 5 μM.  相似文献   

7.
The maximum carboxylation capacity of Rubisco, Vc,max, is an important photosynthetic parameter that is key to accurate estimation of carbon assimilation. The gold‐standard technique for determining Vc,max is to derive Vc,max from the initial slope of an ACi curve (the response of photosynthesis, A, to intercellular CO2 concentration, Ci). Accurate estimates of Vc,max derived from an alternative and rapid “one‐point” measurement of photosynthesis could greatly accelerate data collection and model parameterization. We evaluated the practical application of the one‐point method in six species measured under standard conditions (saturating irradiance and 400 μmol CO2 mol?1) and under conditions that would increase the likelihood for successful estimation of Vc,max: (a) ensuring Rubisco‐limited A by measuring at 300 μmol CO2 mol?1 and (b) allowing time for acclimation to saturating irradiance prior to measurement. The one‐point method significantly underestimated Vc,max in four of the six species, providing estimates 21%–32% below fitted values. We identified ribulose‐1,5‐bisphosphate‐limited A, light acclimation, and the use of an assumed respiration rate as factors that limited the effective use of the one‐point method to accurately estimate Vc,max. We conclude that the one‐point method requires a species‐specific understanding of its application, is often unsuccessful, and must be used with caution.  相似文献   

8.
A mechanistic evaluation of photosynthetic acclimation at elevated CO2   总被引:5,自引:0,他引:5  
Plants grown at elevated pCO2 often fail to sustain the initial stimulation of net CO2 uptake rate (A). This reduced, acclimated, stimulation of A often occurs concomitantly with a reduction in the maximum carboxylation velocity (Vc,max) of Rubisco. To investigate this relationship we used the Farquhar model of C3 photosynthesis to predict the minimum Vc,max capable of supporting the acclimated stimulation in A observed at elevated pCO2. For a wide range of species grown at elevated pCO2 under contrasting conditions we found a strong correlation between observed and predicted values of Vc,max. This exercise mechanistically and quantitatively demonstrated that the observed acclimated stimulation of A and the simultaneous decrease in Vc,max observed at elevated pCO2 is mechanistically consistent. With the exception of plants grown at a high elevated pCO2 (> 90 Pa), which show evidence of an excess investment in Rubisco, the failure to maintain the initial stimulation of A is almost entirely attributable to the decrease in Vc,max and investment in Rubisco is coupled to requirements.  相似文献   

9.
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.  相似文献   

10.
The possible responses of the terrestrial biosphere to future CO2 increases and associated climatic change are being investigated using dynamic global vegetation models (DG VMs) which include the Farquhar et al. (1980) biochemical model of leaf assimilation as the primary means of carbon capture. This model requires representative values of the maximum rates of Rubisco activity, Vmax, and electron transport, Jmax, for different vegetation types when applied at the global scale. Here, we describe an approach for calculating these values based on measurements of the maximum rate of leaf photosynthesis (Amax) 13C discrimination. The approach is tested and validated by comparison with measurements of Rubisco activity assayed directly on wild-type and transgenic Nicotiana tabacum (tobacco) plants with altered Rubisco activity grown under ambient and elevated CO2 mole fractions with high and low N-supply. Vmax and Jmax values are reported for 18 different vegetation types with global coverage. Both variables were linearly related reinforcing the idea of optimal allocation of resources to photosynthesis (light harvesting vs. Rubisco) at the global scale. The reported figures should be of value to the further development of vegetation and ecosystem models employing mechanistic DGVMs.  相似文献   

11.
Paramecium tetraurelia expresses four types of arginine kinase (AK1–AK4). In a previous study, we showed that AK3 is characterized by typical arginine substrate inhibition, where enzymatic activity markedly decreases near a concentration of 1 mM of arginine substrate. This is in sharp contrast to the three other AK types, which obey the Michaelis–Menten reaction curve. Since cellular arginine concentration in another ciliate Tetrahymena is estimated to be 3–15 mM in vivo, Paramecium AK3 likely functions in conditions that are strongly affected by substrate inhibition. The purpose of this work is to find some novel aspect on the kinetic mechanism of the substrate inhibition of Paramecium AK3 enzyme. Substrate inhibition kinetics for AK3 were analyzed using three models and their validity were evaluated with three static parameters (R2, AICc, and Sy.x). The most accurate model indicated that not only ES but also the SES complex reacts to form products, the latter being the complex with two substrates in the active center. The maximum reaction rate for the SES complex, VmaxSES?=?30.4 µmol Pi/min/mg protein, was one-eighth of the ES complex, VmaxES?=?241.7. The dissociation constant for the SES complex (KiSES: 0.34 mM) was two times smaller than that of the ES complex (KsES: 0.61 mM), suggesting that after the primary binding of the arginine substrate (ES complex formation), the binding of a second arginine to the secondarily induced inhibitory site is accelerated to form an SES complex with a lower VmaxSES. The same kinetics were used for the S79A, S80A, and V81A mutants. The results indicate that the S79 residue is significantly involved in the process of binding the second arginine substrate. Herein, the KiSES value was ten times (3.62 mM) the value for the wild-type (0.34 mM), weakening substrate inhibition. In contrast, VmaxES and VmaxSES values for the mutants decreased by one-third, except for the VmaxSES of the S79A mutant, which had a value that was comparable with the value for the wild-type.  相似文献   

12.
The kinetic features of glucose transport in human erythrocytes have been the subject of many studies, but no model is consistent with both the kinetic observations and the characteristics of the purified transporter. In order to reevaluate some of the kinetic features, initial rate measurements were performed at 0°C. The following kinetic parameters were obtained for fresh blood: zero-trans efflux Km = 3.4 mM, Vmax = 5.5 mM/min; infinite-trans efflux Km = 8.7 mM, Vmax = 28 mM/min. For outdated blood, somewhat different parameters were obtained: zero-trans efflux Km = 2.7 mM, Vmax = 2.4 mM/min; infinite-trans efflux Km = 19 mM, Vmax = 23 mM/min. The Km values for fresh blood differ from the previously reported values of 16 mM and 3.4 mM for zero-trans and infinite-trans efflux, respectively (Baker, G.F. and Naftalin, R.J. (1979) Biochim. Biophys. Acta 550, 474–484). The use of 50 mM galactose rather than 100 mM glucose as the infinite-trans sugar produced no change in the infinite-trans efflux Km values but somewhat lower Vmax values. Simulations indicate that initial rates were closely approximated by the experimental conditions. The observed time courses of efflux are inconsistent with a model involving rate-limiting dissociation of glucose from hemoglobin (Naftalin, R.J., Smith, P.M. and Roselaar, S.E. (1985) Biochim. Biophys. Acta 820, 235–249). The results presented here support the adequacy of the carrier model to account for the kinetics.  相似文献   

13.
Photosynthesis limitations in three fern species   总被引:1,自引:0,他引:1  
Maximum photosynthesis rates in ferns are generally lower than those of seed plants, but little is known about the limiting factors, which are crucial to understand the evolution of photosynthesis in land plants. To address this issue, a gas exchange/chlorophyll fluorescence analysis was performed in three fern species spanning high phylogenetic range within Polypodiopsida (Osmunda regalis, Blechnum gibbum and Nephrolepis exaltata) to determine their maximum net photosynthesis (AN), stomatal (gs) and mesophyll (gm) conductances to CO2, and the maximum velocity of carboxylation (Vc,max). The in vitro Rubisco specificity factor (SC/O) was also determined. All three species had values for SC/O similar to those typical of seed plants, but values of AN, gs, gm and Vc,max were within the lowest range of those observed in seed plants. In addition, gs was unresponsive to light and CO2, as already described in other fern species. On the contrary, gm varied with changes CO2. A quantitative photosynthesis limitation analysis suggested that early land plants (ferns) presented not only stomatal limitations—which were less adjustable to the environment—but also restricted gm and Vc,max, resulting in limited maximum photosynthesis rates.  相似文献   

14.
Boreal forests are crucial in regulating global vegetation‐atmosphere feedbacks, but the impact of climate change on boreal tree carbon fluxes is still unclear. Given the sensitivity of global vegetation models to photosynthetic and respiration parameters, we determined how predictions of net carbon gain (C‐gain) respond to variation in these parameters using a stand‐level model (MAESTRA). We also modelled how thermal acclimation of photosynthetic and respiratory temperature sensitivity alters predicted net C‐gain responses to climate change. We modelled net C‐gain of seven common boreal tree species under eight climate scenarios across a latitudinal gradient to capture a range of seasonal temperature conditions. Physiological parameter values were taken from the literature together with different approaches for thermally acclimating photosynthesis and respiration. At high latitudes, net C‐gain was stimulated up to 400% by elevated temperatures and CO2 in the autumn but suppressed at the lowest latitudes during midsummer under climate scenarios that included warming. Modelled net C‐gain was more sensitive to photosynthetic capacity parameters (Vcmax, Jmax, Arrhenius temperature response parameters, and the ratio of Jmax to Vcmax) than stomatal conductance or respiration parameters. The effect of photosynthetic thermal acclimation depended on the temperatures where it was applied: acclimation reduced net C‐gain by 10%–15% within the temperature range where the equations were derived but decreased net C‐gain by 175% at temperatures outside this range. Thermal acclimation of respiration had small, but positive, impacts on net C‐gain. We show that model simulations are highly sensitive to variation in photosynthetic parameters and highlight the need to better understand the mechanisms and drivers underlying this variability (e.g., whether variability is environmentally and/or biologically driven) for further model improvement.  相似文献   

15.
The temperature dependence of C3 photosynthesis is known to vary with growth environment and with species. In an attempt to quantify this variability, a commonly used biochemically based photosynthesis model was parameterized from 19 gas exchange studies on tree and crop species. The parameter values obtained described the shape and amplitude of the temperature responses of the maximum rate of Rubisco activity (Vcmax) and the potential rate of electron transport (Jmax). Original data sets were used for this review, as it is shown that derived values of Vcmax and its temperature response depend strongly on assumptions made in derivation. Values of Jmax and Vcmax at 25 °C varied considerably among species but were strongly correlated, with an average Jmax : Vcmax ratio of 1·67. Two species grown in cold climates, however, had lower ratios. In all studies, the Jmax : Vcmax ratio declined strongly with measurement temperature. The relative temperature responses of Jmax and Vcmax were relatively constant among tree species. Activation energies averaged 50 kJ mol?1 for Jmax and 65 kJ mol?1 for Vcmax, and for most species temperature optima averaged 33 °C for Jmax and 40 °C for Vcmax. However, the cold climate tree species had low temperature optima for both Jmax(19 °C) and Vcmax (29 °C), suggesting acclimation of both processes to growth temperature. Crop species had somewhat different temperature responses, with higher activation energies for both Jmax and Vcmax, implying narrower peaks in the temperature response for these species. The results thus suggest that both growth environment and plant type can influence the photosynthetic response to temperature. Based on these results, several suggestions are made to improve modelling of temperature responses.  相似文献   

16.
Hill-type parameter values measured in experiments on single muscles show large across-muscle variation. Using individual-muscle specific values instead of the more standard approach of across-muscle means might therefore improve muscle model performance. We show here that using mean values increased simulation normalized RMS error in all tested motor nerve stimulation paradigms in both isotonic and isometric conditions, doubling mean simulation error from 9 to 18 (different at p?<?0.0001). These data suggest muscle-specific measurement of Hill-type model parameters is necessary in work requiring highly accurate muscle model construction. Maximum muscle force (F max) showed large (fourfold) across-muscle variation. To test the role of F max in model performance we compared the errors of models using mean F max and muscle-specific values for the other model parameters, and models using muscle-specific F max values and mean values for the other model parameters. Using muscle-specific F max values did not improve model performance compared to using mean values for all parameters, but using muscle-specific values for all parameters but F max did (to an error of 14, different from muscle-specific, mean all parameters, and mean only F max errors at p?≤ 0.014). Significantly improving model performance thus required muscle-specific values for at least a subset of parameters other than F max, and best performance required muscle-specific values for this subset and F max. Detailed consideration of model performance suggested that remaining model error likely stemmed from activation of both fast and slow motor neurons in our experiments and inadequate specification of model activation dynamics.  相似文献   

17.
Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in Järvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c i curves were determined to obtain maximum carboxylation rate (V cmax) and maximum rate of electron transport (J max), whereas needle nitrogen partitioning into carboxylation (P R), bioenergetics associated with electron transport (P B) and thylakoid light harvesting components (P L) was calculated from the values of V cmax, J max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (NM) was generally highest in that stand. The values of LMA were significantly higher and those of NM lower in the 26-year-old stand. Mass-based V cmax and J max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P R, P B and P L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.  相似文献   

18.
We have used the pH variation in the kinetic parameters with respect to malate of NADP-malic enzyme purified from the C4 species, Flaveria trinervia, to compare the pK values of its functional groups with those for the pigeon liver NADP-malic enzyme (MI Schimerlik, WW Cleland [1977] Biochemistry 16: 576-583) and the plant NAD-malic enzyme (KO Willeford, RT Wedding [1987] Plant Physiol 84: 1084-1087). Like the other enzymes, the C4 enzyme has a group with a pK of about 6.0 (6.6 for the C4 enzyme), as indicated from plots of the log Vmax/Km (Vmax = maximum rate of catalysis) versus pH, which must lose a proton for malate binding and subsequent catalysis. The optimum ionization for the C4 enzyme-NADP-Mg2+ complex occurs at pH 7.1 to 7.5. From pH 7.5 to 8.4, the Km increases, but Vmax remains constant. The log Vmax/Km plot in this pH range indicates a group with a pK of about 7.7. The other malic enzymes exhibit a similar pK. Above pH 8.4, deprotonation leads to a marked increase in Km and a decrease in Vmax for the C4 enzyme. As in the case of the animal enzyme, the log Vmax/Km plot for the C4 enzyme appears to approach a slope of two. The curve suggests an average pK of 8.4 for the groups involved, while the animal enzyme exhibits an average pK of 9.0. The NAD-malic enzyme does not exhibit any pK values at these high pK values. We hypothesize that the putative groups with the high pK values may be at least partially responsible for the ability of the C4 NADP-malic enzyme to maintain high activity at pH 8.0 in illuminated chloroplasts.  相似文献   

19.
Photosynthetic 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.  相似文献   

20.
Efficient methods for accurate and meaningful high-throughput plant phenotyping are limiting the development and breeding of stress-tolerant crops. A number of emerging techniques, specifically remote sensing methods, have been identified as promising tools for plant phenotyping. These remote sensing methods can be used to accurately and rapidly relate variations in leaf optical properties with important plant characteristics, such as chemistry, morphology, and photosynthetic properties at the leaf and canopy scales. In this study, we explored the potential to utilize optical (λ = 500–2,400 nm) near-surface remote sensing reflectance spectroscopy to evaluate the effects of ozone pollution on photosynthetic capacity of soybean (Glycine max Merr.). The research was conducted at the Soybean Free Air Concentration Enrichment (SoyFACE) facility where we subjected plants to ambient (44 nL L?1) and elevated ozone (79–82 nL L?1 target) concentrations throughout the growing season. Exposure to elevated ozone resulted in a significant loss of productivity, with the ozone-treated plants displaying a ~30 % average decrease in seed yield. From leaf reflectance data, it was also clear that elevated ozone decreased leaf nitrogen and chlorophyll content as well as the photochemical reflectance index (PRI), an optical indicator of the epoxidation state of xanthophyll cycle pigments and thus physiological status. We assessed the potential to use leaf reflectance properties and partial least-squares regression (PLSR) modeling as an alternative, rapid approach to standard gas exchange for the estimation of the maximum rates of RuBP carboxylation (V c,max), an important parameter describing plant photosynthetic capacity. While we did not find a significant impact of ozone fumigation on V c,max, standardized to a reference temperature of 25 °C, the PLSR approach provided accurate and precise estimates of V c,max across ambient plots and ozone treatments (r 2 = 0.88 and RMSE = 13.4 μmol m?2 s?1) based only on the variation in leaf optical properties and despite significant variability in leaf nutritional status. The results of this study illustrate the potential for combining the phenotyping methods used here with high-throughput genotyping methods as a promising approach for elucidating the basis for ozone tolerance in sensitive crops.  相似文献   

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