How plants interact with sunlight is central to the existence of life and provides a means of examining spatial patterns of photosynthesis over broad spatial scales using remote sensing. Although the basic properties of vegetation reflectance have been known for decades, interpreting spectral patterns of whole ecosystems is challenging because leaf-level effects are complicated by a host of stem- and canopy-level traits. In recent years, several studies have demonstrated that solar‐induced chlorophyll fluorescence (SIF) offers an alternative means of estimating terrestrial gross primary production. However, it remains unclear whether relationships vary across biomes or whether a robust, universal relationship exists across a variety of biomes. Here, we conducted a global analysis of the relationship between SIF measured at 1.3 km × 2.25 km resolution from the Orbiting Carbon Observatory‐2 (OCO‐2) and GPP from 64 eddy covariance flux tower sites encompassing eight major biomes.
Results/Conclusions
OCO‐2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R2 = 0.72). Strong linear relationships between SIF and GPP were consistently found for all biomes except evergreen broadleaf forests at the daily timescale. The generally consistent slope of the relationship among biomes suggests a nearly universal rather than biome‐specific SIF–GPP relationship. SIF was mainly driven by absorbed photosynthetically active radiation and was also influenced by environmental stresses (temperature and water limitations) that determine photosynthetic light use efficiency. OCO‐2 SIF generally had a better performance for predicting GPP than satellite‐derived vegetation indices and a light use efficiency model. The universal SIF–GPP relationship can potentially lead to more accurate GPP estimates regionally or globally. OCO-2 SIF exhibited much stronger correlation with tower GPP than MODIS-derived NDVI, EVI, and NIR and slightly stronger relationship with tower GPP than BRDF-corrected EVI (EVIBRDF: R2=0.64) and NIR (NIRv_BRDF: R2=0.65).