Disentangling leaf physiology and canopy structure effects on solar-induced chlorophyll fluorescence and gross primary productivity: A multi-biome and cross-site assessment

Solar-induced chlorophyll fluorescence (SIF) is a powerful tool for estimating terrestrial gross primary productivity (GPP). However, the mechanistic link between SIF and GPP remains unclear across different biomes and sites. This is primarily due to the coupled effects of leaf physiology and canopy structure on canopy SIF signals. To disentangle their relative contributions, we combined flux tower observations with GOSIF data to analyze the relationships among light use efficiency (LUE), fluorescence yield (ΦF), and canopy escape ratio ( f esc ) across 37 sites covering four typical biomes (CRO, GRA, ENF, DBF). The results indicated that f esc generally strengthened the relationship between ΦF and LUE across biomes with contrasting canopy structures. However, this enhancement was biome-specific, being notably significant in CRO, GRA, and ENF, where R 2 increased by 0.10–0.15 (a relative increase of 21%–88%). Consistent with these findings, correcting observed SIF to total emitted SIF using f esc tended to weaken the SIF-GPP correlation. We further found that the divergent responses of LUE and ΦF to environmental factors were associated with variations in the slope and correlation of the SIF-GPP relationship along environmental gradients. Specifically, except for ENF, relatively high SIF-GPP correlations for CRO, GRA, and DBF were mainly observed in temperature bins above approximately 9 °C and VPD bins below approximately 14 hPa. Furthermore, the SIF-GPP relationship exhibited site heterogeneity attributed to the influence of both canopy structure and leaf traits. These findings highlight the need to consider canopy structure, physiological regulation, and site-level variability when using satellite SIF to estimate terrestrial GPP.