Modeling light response of effective quantum efficiency of photosystem II for C₃ and C₄ crops

Effective quantum efficiency of photosystem II (Φ_PSII) 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 Φ_PSII (Φ_PSII-I) over the I range from zero to high irradiance levels is lacking. In this study, we tested a Φ_PSII-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 Φ_PSII-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 Φ_PSII 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.