Photosynthetic Gas Exchange in Land Plants at the Leaf Level.

Leaf-level gas exchange enables insights into the physiology and in vivo biochemical processes of plants. Advances in infrared gas analysis have resulted in user-friendly off-the-shelf gas exchange systems that allow researchers to collect physiological measurements with the push of a few buttons. Here, I describe how to set up the gas exchange equipment, what to pay attention to while making measurements, and provide some guidelines on how to analyze and interpret the data obtained.

[Examining effects of salt stress on leaf photosynthesis of cotton based on the FvCB model]. / 基于FvCBæ¨¡åž‹åˆ†æžç›åˆ†èƒè¿«å¯¹æ£‰èŠ±å¶ç‰‡å ‰åˆä½œç”¨çš„å½±å“.

To understand the responsive mechanism of leaf photosynthesis of cotton to salinity stress, we investigated the effects of salt stress on leaf photosynthetic characteristics of cotton seedlings with the FvCB model under five levels of salt concentration, i.e., 0 (CK), 50, 100, 150 and 200 mmol·L-1. Results showed that, compared with CK, the salt concentrations of 50 and 100 mmol·L-1 increased the maximum carboxylation rate (Vc max) and the maximum electron transport rate (Jmax), while the salt concentrations of 150 and 200 mmol·L-1 significantly decreased Vc max and Jmax. The net photosynthetic rate (Pn), mesophyll conductance (gm) and dark respiration rate (Rd) gradually decreased with the increases of salt concentration. Compared with CK, the salt concentrations of 50 and 100 mmol·L-1 did not affect gm, but significantly decreased Pn and Rd. The salt concentrations of 150 and 200 mmol·L-1 significantly decreased Pn, gm and Rd, which were significantly different from the salt concentrations of 0, 50 and 100 mmol·L-1. Pn of cotton seedlings under different salt concentrations was simulated by the FvCB model. Compared with the results from the FvCB model without considering gm, the FvCB model with gm improved the determination coefficient between the simulated and measured values and decreased the mean absolute error. The salinity threshold of cotton seedlings ranged between 100 and 150 mmol·L-1. With the increases of salt concentration, the limiting factor of leaf photosynthesis changed from mesophyll conductance to impaired components of photosynthetic apparatus. The FvCB model combined gm could improve the accuracy of photosynthesis simulation.

Sensitivity analysis and estimation using a hierarchical Bayesian method for the parameters of the FvCB biochemical photosynthetic model.

Photosynthesis is a major process included in land surface models. Accurately estimating the parameters of the photosynthetic sub-models can greatly improve the ability of these models to accurately simulate the carbon cycle of terrestrial ecosystems. Here, we used a hierarchical Bayesian approach to fit the Farquhar-von Caemmerer-Berry model, which is based on the biochemistry of photosynthesis using 236 curves for the relationship between net CO2 assimilation and changes in the intercellular CO2 concentration. An advantage of the hierarchical Bayesian algorithm is that parameters can be estimated at multiple levels (plant, species, plant functional type, and population level) simultaneously. The parameters of the hierarchical strategy were based on the results of a sensitivity analysis. The Michaelis-Menten constant (Kc25), enthalpies of activation (EJ and EV), and two optical parameters (θ and α) demonstrated considerable variation at different levels, which suggests that this variation cannot be ignored. The maximum electron transport rate (Jmax25), maximum rate of Rubisco activity (Vcmax25), and dark respiration in the light (Rd25) were higher for broad-leaved plants than for needle-leaved plants. Comparison of the model's simulated outputs with observed data showed strong and significant positive correlations, particularly when the model was parameterized at the plant level. In summary, our study is the first effort to combine sensitivity analysis and hierarchical Bayesian parameter estimation. The resulting realistic parameter distributions for the four levels provide a reference for current and future land surface models. Furthermore, the observed variation in the parameters will require attention when using photosynthetic parameters in future models.

Surfing the Hyperbola Equations of the Steady-State Farquhar-von Caemmerer-Berry C3 Leaf Photosynthesis Model: What Can a Theoretical Analysis of Their Oblique Asymptotes and Transition Points Tell Us?

The asymptotes and transition points of the net CO2 assimilation (A/Ci) rate curves of the steady-state Farquhar-von Caemmerer-Berry (FvCB) model for leaf photosynthesis of C3 plants are examined in a theoretical study, which begins from the exploration of the standard equations of hyperbolae after rotating the coordinate system. The analysis of the A/Ci quadratic equations of the three limitation states of the FvCB model-abbreviated as Ac, Aj and Ap-allows us to conclude that their oblique asymptotes have a common slope that depends only on the mesophyll conductance to CO2 diffusion (gm). The limiting values for the transition points between any two states of the three limitation states c, j and p do not depend on gm, and the results are therefore valid for rectangular and non-rectangular hyperbola equations of the FvCB model. The analysis of the variation of the slopes of the asymptotes with gm casts doubts about the fulfilment of the steady-state conditions, particularly, when the net CO2 assimilation rate is inhibited at high CO2 concentrations. The application of the theoretical analysis to extended steady-state FvCB models, where the hyperbola equations of Ac, Aj and Ap are modified to accommodate nitrogen assimilation and amino acids export via the photorespiratory pathway, is also discussed.

Photosynthetic Gas Exchange in Land Plants at the Leaf Level.

Leaf-level gas exchange enables insights into the physiology and in vivo biochemical processes of plants. Advances in infrared gas analysis have resulted in user-friendly off-the-shelf gas exchange systems that allow researchers to collect physiological measurements with the push of a few buttons. Here, I describe how to set up the gas exchange equipment and what to pay attention to while making measurements, and provide some guidelines on how to analyze and interpret the data obtained.

[Photo-physiological and photo-biochemical characteristics of several herbaceous and woody species based on FvCB model]. / 基于FvCBæ¨¡åž‹çš„å‡ ç§è‰æœ¬å’Œæœ¨æœ¬æ¤ç‰©å ‰åˆç”Ÿç†ç”ŸåŒ–ç‰¹æ€§.

To explore the photosynthetic capacity and the leaf photosynthetic apparatus for plants with different life forms, CO2 response curves of 7 woody species and 4 herbaceous species were fitted by the modified rectangular hyperbolic model and the FvCB model, and the photosynthetic parameters, including maximum net photosynthetic rate (Pn max), maximal Rubisco carboxylation rate (Vc max), maximal electron transport rate (Jmax), day respiration (Rd), and mesophyll resistance to CO2 transport (rm), were compared among different woody species, among different herbaceous species, and between woody and herbaceous life-forms, respectively. The results showed Pn max of seven woody species descended in the order of Sapium sebiferum and Boehmeria nivea ＞ Machilus pingii and Pittosporum tobira ＞ Cyclobalanopsis glauca, Castanopsis sclerophylla, and Quercus nuttallii. Vc max of S. sebiferum, B. nivea, M. pingii, and P. tobira was significantly higher than that of C. glauca and C. sclerophylla. Jmax of woody species was in descending order as S. sebiferum ＞ B. nivea and P. tobira ＞ Q. nuttallii, C. sclerophylla, and C. glauca. rm of M. pingii and C. sclerophylla was higher than that of S. sebiferum, P. tobira and B. nivea. Pn max of Phytolacca acinosa was significantly higher than that of Ageratum conyzoides and Achyranthes aspera. There was no significant difference in Vc max among 4 herbaceous species. Jmax of P. acinosa was higher than that of A. conyzoides. rm of S. nigrum and A. aspera was higher than that of A. conyzoides. Rd of P. acinosa was higher than that of A. conyzoides and A. aspera. The photosynthetic parameters (Pn max, Vc max, Jmax and rm) of woody species were significantly higher than those of herbaceous species, but no significant difference was found in Rd between woody and herbaceous species. In conclusion, the difference in photosynthetic capacity among different species and between the two plant life-forms resulted from the difference in Rubisco carboxylation capacity, electron transport capacity, and mesophyll resistance among these species.

Sweet Pepper (Capsicum annuum L.) Canopy Photosynthesis Modeling Using 3D Plant Architecture and Light Ray-Tracing.

Canopy photosynthesis has typically been estimated using mathematical models that have the following assumptions: the light interception inside the canopy exponentially declines with the canopy depth, and the photosynthetic capacity is affected by light interception as a result of acclimation. However, in actual situations, light interception in the canopy is quite heterogenous depending on environmental factors such as the location, microclimate, leaf area index, and canopy architecture. It is important to apply these factors in an analysis. The objective of the current study is to estimate the canopy photosynthesis of paprika (Capsicum annuum L.) with an analysis of by simulating the intercepted irradiation of the canopy using a 3D ray-tracing and photosynthetic capacity in each layer. By inputting the structural data of an actual plant, the 3D architecture of paprika was reconstructed using graphic software (Houdini FX, FX, Canada). The light curves and A/C i curve of each layer were measured to parameterize the Farquhar, von Caemmerer, and Berry (FvCB) model. The difference in photosynthetic capacity within the canopy was observed. With the intercepted irradiation data and photosynthetic parameters of each layer, the values of an entire plant's photosynthesis rate were estimated by integrating the calculated photosynthesis rate at each layer. The estimated photosynthesis rate of an entire plant showed good agreement with the measured plant using a closed chamber for validation. From the results, this method was considered as a reliable tool to predict canopy photosynthesis using light interception, and can be extended to analyze the canopy photosynthesis in actual greenhouse conditions.

Disentangling the contributions of osmotic and ionic effects of salinity on stomatal, mesophyll, biochemical and light limitations to photosynthesis.

There are conflicting opinions on the relative importance of photosynthetic limitations under salinity. Quantitative limitation analysis of photosynthesis provides insight into the contributions of different photosynthetic limitations, but it has only been applied under saturating light conditions. Using experimental data and modelling approaches, we examined the influence of light intensity on photosynthetic limitations and quantified the osmotic and ionic effects of salinity on stomatal (LS ), mesophyll (LM ), biochemical (LB ) and light (LL ) limitations in cucumber (Cucumis sativus L.) under different light intensities. Non-linear dependencies of LS , LM and LL to light intensity were found. Osmotic effects on LS and LM increased with the salt concentration in the nutrient solution (Ss ) and the magnitude of LM depended on light intensity. LS increased with the Na(+) concentration in the leaf water (Sl ) and its magnitude depended on Ss . Biochemical capacity declined linearly with Sl but, surprisingly, the relationship between LB and Sl was influenced by Ss . Our results suggest that (1) improvement of stomatal regulation under ionic stress would be the most effective way to alleviate salinity stress in cucumber and (2) osmotic stress may alleviate the ionic effects on LB but aggravate the ionic effects on LS .