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Modeling light response of effective quantum efficiency of photosystem II for C3 and C4 crops
Effective quantum efficiency of photosystem II (ΦPSII) represents the proportion of photons of incident light that are actually used for photochemical processes, which is a key determinant of crop photosynthetic efficiency and productivity. A robust model that can accurately reproduce the nonlinear light response of ΦPSII (ΦPSII–I) over the I range from zero to high irradiance levels is lacking. In this study, we tested a ΦPSII–I model based on the fundamental properties of light absorption and transfer of energy to the reaction centers via photosynthetic pigment molecules. Using a modeling-observation intercomparison approach, the performance of our model versus three widely used empirical ΦPSII–I models were compared against observations for two C3 crops (peanut and cotton) and two cultivars of a C4 crop (sweet sorghum). The results highlighted the significance of our model in (1) its accurate and simultaneous reproduction of light response of both ΦPSII and the photosynthetic electron transport rate (ETR) over a wide I range from light limited to photoinhibition I levels and (2) accurately returning key parameters defining the light response curves.
Adaptive significance of age- and light-related variation in needle structure, photochemistry, and pigments in evergreen coniferous trees
Investigation on absorption cross-section of photosynthetic pigment molecules based on a mechanistic model of the photosynthetic electron flow-light response in C3, C4 species and cyanobacteria grown under various conditions
Investigation on intrinsic properties of photosynthetic pigment molecules participating in solar energy absorption and excitation, especially their eigen-absorption cross-section (σik) and effective absorption cross-section (σ′ik), is important to understand photosynthesis. Here, we present the development and application of a new method to determine these parameters, based on a mechanistic model of the photosynthetic electron flow-light response. The analysis with our method of a series of previously collected chlorophyll a fluorescence data shows that the absorption cross-section of photosynthetic pigment molecules has different values of approximately 10−21 m2, for several photosynthetic organisms grown under various conditions: (1) the conifer Abies alba Mill., grown under high light or low light; (2) Taxus baccata L., grown under fertilization or non-fertilization conditions; (3) Glycine max L. (Merr.), grown under a CO2 concentration of 400 or 600 μmol CO2 mol−1 in a leaf chamber under shaded conditions; (4) Zea mays L., at temperatures of 30°C or 35°C in a leaf chamber; (5) Osmanthus fragrans Loureiro, with shaded-leaf or sun-leaf; and (6) the cyanobacterium Microcystis aeruginosa FACHB905, grown under two different nitrogen supplies. Our results show that σik has the same order of magnitude (approximately 10−21 m2), and σ′ik for these species decreases with increasing light intensity, demonstrating the operation of a key regulatory mechanism to reduce solar absorption and avoid high light damage. Moreover, compared with other approaches, both σik and σ′ik can be more easily estimated by our method, even under various growth conditions (e.g., different light environment; different CO2, NO2, O2, and O3 concentrations; air temperatures; or water stress), regardless of the type of the sample (e.g., dilute or concentrated cell suspensions or leaves). Our results also show that CO2 concentration and temperature have little effect on σik values for G. max and Z. mays. Consequently, our approach provides a powerful tool to investigate light energy absorption of photosynthetic pigment molecules and gives us new information on how plants and cyanobacteria modify their light-harvesting properties under different stress conditions.
Addressing the long-standing limitations of double exponential and non-rectangular hyperbolic models in quantifying light-response of electron transport rates in different photosynthetic organisms under various conditions
The models used to describe the light response of electron transport rate in photosynthesis play a crucial role in determining two key parameters i.e., the maximum electron transport rate (Jmax) and the saturation light intensity (Isat). However, not all models accurately fitJ–Icurves, and determine the values ofJmaxandIsat. Here, three models, namely the double exponential (DE) model, the non-rectangular hyperbolic (NRH) model, and a mechanistic model developed by one of the coauthors (Z-P Ye) and his coworkers (referred to as the mechanistic model), were compared in terms of their ability to fitJ–Icurves and estimateJmaxandIsat. Here, we apply these three models to a series of previously collected Chlafluorescence data from seven photosynthetic organisms, grown under different conditions. Our results show that the mechanistic model performed well in describing theJ–Icurves, regardless of whether photoinhibition/dynamic down-regulation of photosystem II (PSII) occurs. Moreover, bothJmaxandIsatestimated by this model are in very good agreement with the measured data. On the contrary, although the DE model simulates quite well theJ–Icurve for the species studied, it significantly overestimates both theJmaxofAmaranthus hypochondriacusand theIsatofMicrocystis aeruginosagrown under NH4+-N supply. More importantly, the light intensity required to achieve the potential maximum ofJ(Js) estimated by this model exceeds the unexpected high value of 105μmol photons m−2s−1forTriticum aestivumandA. hypochondriacus. The NRH model fails to characterize theJ-Icurves with dynamic down-regulation/photoinhibition forAbies alba,Oryza sativaandM. aeruginosa. In addition, this model also significantly overestimates the values ofJmaxforT. aestivumat 21% O2andA. hypochondriacusgrown under normal condition, and significantly underestimates the values ofJmaxforM. aeruginosagrown under NO3–N supply. Our study provides evidence that the ‘mechanistic model’ is much more suitable than both the DE and NRH models in fitting theJ–Icurves and in estimating the photosynthetic parameters. This is a powerful tool for studying light harvesting properties and the dynamic down-regulation of PSII/photoinhibition.