Difference in seasonal peak timing of soybean far-red SIF and GPP explained by canopy structure and chlorophyll content

Recent advances in remotely sensed solar-induced chlorophyll fluorescence (SIF) have provided an exciting and promising opportunity for estimating gross primary production (GPP). Previous studies mainly focused on the linear correlation between SIF GPP slope of SIF-GPP relationship, both which lack rigorous consideration seasonal trajectories GPP. Here, we investigated timing peaks far-red soybean fields by integrating tower data, satellite process-based Soil Canopy Observation Photosynthesis Energy (SCOPE, v2.0) model simulations. We found inconsistency peak three four based eddy-covariance measurements. In particular, reached its maximum 14–17 days earlier than This difference degraded sunny-day at daily scale (Pearson r = 0.83–0.87 site with Pearson 0.96 no difference), it can be explained a divergence seasonality absorbed photosynthetic active radiation (APAR) canopy content (ChlCanopy). that - byproduct light reactions photosynthesis was primarily controlled APAR, whereas dominated ChlCanopy. Further, SCOPE simulations showed patterns leaf area index (LAI), (ChlLeaf) angle distribution (LAD) could affect different consequently relationship A further increase LAI after fraction absorption (FPAR) saturates later ChlLeaf compared to results SIF. More horizontal angles exacerbate this difference. Our advance mechanistic understanding relationships combining information potentially improve remote-sensing-based estimation.