Seasonal variations of sun-induced chlorophyll fluorescence from leaf to canopy level and its relations with plant functional traits for paddy-rice

Chlorophyll fluorescence of vegetation has been rigorously used as a direct proxy of actual photosynthetic activity. While recent development of satellite sun-induced chlorophyll fluorescence (SIF) has stimulated the research to monitor photosynthetic function, our understanding of the covariation between leaf and canopy SIF and their seasonal link to plant functional traits is still limited. The link between SIF, and leaf traits (chlorophyll content, Cab, and maximum carboxylation rate, V_cmax) are of great significance for understanding the mechanism between SIF and photosynthesis. In this work, we investigated the seasonal variations of SIF from leaf to canopy level and their link to leaf traits across different plant growth stage. Leaf and canopy SIF were measured concurrently during the growing season of 2017 in a paddy rice field. Our results confirmed that a significant consistency exists between leaf and canopy SIF over the growing season but varies with plant growth stages. The relationship between SIF and Cab and V_cmax is found to be depending on the plant growth stage with significant correlation after flowering period. Our findings shows that after the flowering period at both leaf scale and canopy scale, the seasonal variation of SIF is highly consistent (R²=0.78, P<0.05). SIF yield is strongly correlated with Cab and V_cmax at leaf scale (R²=0.78, P<0.05; R²=0.79, P<0.05) and SIF is significantly related to Cab and V_cmax at canopy scale (R²=0.77, P<0.05; R²=0.81, P<0.05). SIF contains important information of Cab and V_cmax, and this is of great significance for building the foundation and direction of a more complete theory of sun-induced fluorescence application.