A broadly applicable biophysical model of photosynthesis and its application for SIF remote sensing

Abstract:

Plants possess sophisticated mechanisms to balance the light and carbon reactions of photosynthesis, a condition vital to the normal functioning of photosynthetic apparatus and long-term species survival. In theory, photosynthesis could be predicted from either the light or carbon reactions with convergence expected. Historically, mechanistic modeling efforts have focused on carbon reactions. This traditional focus is challenged in the era of growing interest in crop engineering for better photosynthetic efficiency and in using sun-induced chlorophyll fluorescence (SIF) to monitor photosynthesis at canopy scales and beyond; both efforts depend on our predictive capability of not just carbon but also light reactions. We have developed a closed biophysical representation of light reactions to model photosynthesis, SIF and the balance between light and carbon reactions. We achieve this closure by developing models of photochemical and non-photochemical electron transport regulations (PNPETRs) with environmental variables as direct predictors. The PNPETR models, which capture the feedforward and feedback interactions between light and carbon reactions, are coupled with light reaction equations derived from the law of conservation of energy to resolve relevant dynamic light reaction variables and CO₂ assimilation rate. This biophysical model of photosynthesis accurately predicts fluorometry and gas exchange measurements of multiple crop and tree species across broad environmental conditions. It establishes the light reaction basis for photosynthetic remote sensing, provides an analytical solution for simulating the light-carbon reaction balance for crop engineering, and complements carbon reaction models as a comprehensive framework for system modeling of photosynthetic responses to increased atmospheric CO₂ and climate change. Implications of the biophysical model of photosynthesis for SIF remote sensing will be discussed.