Escape Ratio Contributes More Than Fluorescence Yield to SIF-GPP Relationship Over Crops and Rainforest

Solar-induced chlorophyll fluorescence (SIF) is an effective indicator to track the gross primary productivity (GPP). However, there is still a lack of a clear understanding for the contribution of physiological and structural factors to the SIF-GPP relationship at the canopy scale. To quantify the influence of different SIF components, particularly the photon escape ratio ( ${f}_{\text {esc}}$ ) and fluorescence yield ( ${\Phi }_{F}$ ), on the SIF-GPP relationship, this study evaluated the performance of various vegetation indices (VIs), SIF components, light use efficiency (LUE), and GPP over two typical biomes (crops and rainforest), using a range of satellite remote sensing products. In August of each year from 2018 to 2020, both SIF and GPP over United States (U.S.) Corn Belt are higher than those over the Amazon rainforest, attributed to the consistent pattern of higher $f_{\text {esc}}$ and LUE over crops than over rainforest, as well as ${\Phi }_{F}$ . Furthermore, the structural signals represented by ${f}_{\text {esc}}$ ( $R =0.41$ –0.64) can better capture the LUE variations than $\boldsymbol {\Phi }_{F}$ ( $R =0.10$ –0.30) for each biome. This study highlights that $f_{\text {esc}}$ , determined by canopy structure, has great potential to capture LUE and GPP changes within and across biomes.