Seasonal variations in the relationships between sun-induced chlorophyll fluorescence and photosynthetic capacity from leaf to canopy in a rice paddy.

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 potential for estimating Vcmax at the ecosystem level. However, the SIF-Vcmax relationship at leaf and canopy levels is still poorly understood. This study investigates the dynamic relationship between SIF and Vcmax and its controlling factors using SIF and CO2 response measurements in rice. The results show that SIF and its yield (SIFy) are strongly correlated with Vcmax during the growing season, though the relationship varies with rice growth stages. After flowering, SIFy has a stronger relationship with Vcmax than SIF flux does 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. 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.