Satellite retrievals of Solar-Induced chlorophyll Fluorescence (SIF) offers a promising tool to remotely monitor photosynthesis for the globe. However, the diurnal dynamics of SIF as well as the eco-physiological and environmental drivers for its coupling with photosynthesis remain elusive. This prevents not only an accurate temporal scaling from instantaneous SIF measurements to GPP fluxes but also interpreting the satellite retrievals in a biologically meaningful way. In this project, we used two maize sites with contrasting canopy architecture and management practices to understand the diurnal cycle of SIF measured by a tower and an Unmanned Aerial Vehicle (UAV) platform during the 2018 and 2019 growing seasons. In addition, we made concurrent measurements of hyperspectral reflectance, leaf gas exchanges, PAM fluorometry, and leaf water potential.
Results/Conclusions
We found that the diurnal shape of SIF is highly sensitive to retrieval methods. This may further impact measured diurnal SIF dynamics on top of contribution from canopy structure and non-photochemical quenching, and result in mis-interpretations of the SIF-photosynthesis relationship. In addition, attribution of SIF diurnal dynamics to canopy structure and plant physiology varies with phenological stages and sky conditions. These findings have important implications for upscaling and interpreting satellite SIF retrievals for estimation of GPP at large scale.