Can SIF and NPQ be used in the photosynthesis rate simulation of plants subjected to drought?

Solar-induced chlorophyll fluorescence (SIF) has been used to estimate leaf-level net CO 2 assimilation by a mechanistic light reaction (MLR-SIF) equation. However, the application of this model would be limited by the challenging measurement and estimation of input parameters (e.g. fraction of open PSII reaction centres, q L ). We modified the MLR-SIF model by replacing q L by the easily obtained parameters (non-photochemical quenching [NPQ]) to facilitate its application. We employed synchronous measurements of gas exchanges, ChlF parameters and SIF for Leymus chinensis , Populus tomentosa Carrières and Ulmus pumila var. sabulosa under the soil–water deficit and rehydration process to test the robustness of the modified MLR-SIF model. Our results demonstrated that for L. chinensis the net photosynthesis rate dynamics under severe soil–water stress and saturated water condition were effectively captured by the modified MLR-SIF model ( R 2 = 0.75–0.92, RMSE = 1.11–3.56) . For P. tomentosa Carrières and U. pumila var. sabulosa , the net photosynthesis rates were predicted by the modified MLR-SIF model with good accuracy ( R 2 = 0.86, RMSE = 9.44; R 2 = 0.88, RMSE = 4.16) across the water deficit and rehydration condition . However, the electron transport rate estimated by the modified MLR-SIF model uncoupled with the photosynthetic capacity ( r 2 = -0.13) and lowered the net photosynthesis rate simulation precision ( R 2 = 0.35, RMSE = 3.41) for L. chinensis under mild drought stress and saturated light intensities. The electron transport rate estimated by the modified MLR-SIF model downregulated the photosynthetic capacity for P. tomentosa Carrières ( r 2 = 0.32) and U. pumila var. sabulosa ( r 2 = 0.22) under mild drought stress. The shift of the Rubisco and RUBP limited state cross-points, the dynamic photosynthesis parameters across the plant species and the alternative electron sinks under soil–water deficit and rehydration process influenced the simulation precision of the modified MLR-SIF model. Our modified MLR-SIF model provided a basis for understanding and inferring the photosynthetic rate by SIF and NPQ under water stress.

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