Constraining water limitation of photosynthesis in a crop growth model with sun-induced chlorophyll fluorescence.

Water fulfils key roles in maintaining a plant's biological activity. Water shortage induces stomatal closure, causing a reduction in photosynthesis and transpiration rates. Sun-induced chlorophyll fluorescence (SIF) emission is sensitive to subtle, stress-induced variations in non-photochemical quenching and in photosynthetic electron transport, caused by e.g., a fluctuation in the water availability. Based on this sensitivity, a framework for calibrating a water stress function in a crop growth model using ground-based SIF observations is proposed. SIF time series are simulated by coupling the AgroC crop growth model to the Soil Canopy Observations Photosynthesis Energy (SCOPE) model. This allowed parametrizing the water stress function in the AgroC crop growth model, resulting in improved estimates of actual evapotranspiration and net ecosystem exchange over a sugar beet stand during stressed periods. The improvement in the estimation of the water and carbon fluxes by AgroC during the summer months highlights the ability of canopyscale SIF observations to serve as a remote sensing metric to indicate the intensity of a stress condition. We argue that our framework, linking SIF emission to stress functions, can be used to extract information concerning drought stress from the Fluorescence Explorer (FLEX) satellite, scheduled for launch in 2024. • The biochemical component of SIF emission is sensitive to drought stress. • Drought stress can be accounted for by decreasing the carboxylation capacity and by increasing the non-photochemical quenching. • A reduction in VCMax and an increase in NPQ translate into a decrease in SIF and photosynthetic activity. • Using SIF observations, a water stress function can be calibrated in a crop growth model. • A better parametrization of the water stress function improves estimates of water and carbon fluxes. [ABSTRACT FROM AUTHOR]