Seasonally varying relationship between sun-induced chlorophyll fluorescence and photosynthetic capacity from leaf to canopy in a paddy rice field

Abstract

Photosynthetic capacity (leaf maximum carboxylation rate, Vcmax) is a critical parameter for accurately assessing carbon assimilation by plant canopies. Recent studies of sun-induced chlorophyll fluorescence (SIF) show the potential to estimate Vcmax at the ecosystem level. However, the SIF-Vcmax relationship at leaf and canopy levels are still poorly understood. This study investigates the relationship between leaf or canopy SIF and leaf Vcmax and its controlling factors based on SIF and CO2 response measurements in rice. The results show that SIF (or its yield, SIFy) and Vcmax are strongly correlated during the growing season, though the relationship varies with rice growth stages. After the flowering period, SIFy has a stronger relationship with Vcmax than SIF flux at both leaf and canopy levels. Further analysis suggests that changes in canopy structure and leaf physiology lead to the divergence of the link between SIF and Vcmax from leaf to canopy level. Our findings highlight the need to account for plant physiology and canopy structure in interpreting the SIF signal across spatial scales. Our observation-based results provide evidence that remotely sensed SIF observations can be used to track seasonal variations of Vcmax at the leaf and canopy levels.