Uncertainties in linking solar-induced chlorophyll fluorescence to plant photosynthetic activities

Solar-induced chlorophyll fluorescence (SIF) is related to photosynthesis and can serve as a remote sensing proxy for estimating photosynthetic energy conversion and carbon uptake. In this paper, three key factors affecting the relationship between SIF and gross primary production (GPP) were investigated using both models and observations on winter wheat (C3 crop) and maize (C4 crop). Firstly, the bidirectional SIF emission was investigated by multi-angular spectral measurement, which was found to be similar to that of the canopy reflectance in the solar principal plane. Secondly, the wavelength dependent predictive power of SIF to estimate GPP was assessed using diurnal observations on winter wheat. As indicated by the preliminary studies, the far-red SIF may be more reliable for remote sensing of GPP than the red SIF due to the heterogeneous and diverse vegetation growth status at regional or global scale. Finally, the potential of far-red SIF to track the diurnal and seasonal variations in GPP for C3 and C4 crops was investigated, and the result show that the GPP SIF relationship is dependent on the type of photosynthesis.