Diurnal and Seasonal Dynamics of Solar‐Induced Chlorophyll Fluorescence, Vegetation Indices, and Gross Primary Productivity in the Boreal Forest

Remote sensing of solar-induced chlorophyll fluorescence (SIF) provides a powerful proxy for gross primary productivity (GPP). It is particularly promising in boreal ecosystems where seasonal downregulation photosynthesis occurs without significant changes canopy structure or content. The use SIF as GPP complicated by inherent non-linearities due to both physical (illumination effects) and ecophysiological (light efficiencies) controls at fine spatial (tower/leaf) temporal (half-hourly) scales. To study the SIF-GPP relationship, we investigated diurnal dynamics continuous tower-based measurements SIF, GPP, common vegetation indices Southern Old Black Spruce Site (SOBS) Saskatchewan, CA over course two years. We find that outperforms other all scales but shows non-linear relationship with half-hourly resolution. At small scales, are predominantly driven light non-linearity between saturation GPP. Averaged daily monthly linear reduction observed PAR range. Seasonal responses efficiency which co-vary temperature, while illumination partially linearize relationship. Additionally, has dependency. Our results help clarify utility estimating carbon assimilation forests.