Li, X; Xiao, JF (2020). Global climatic controls on interannual variability of ecosystem productivity: Similarities and differences inferred from solar-induced chlorophyll fluorescence and enhanced vegetation index. AGRICULTURAL AND FOREST METEOROLOGY, 288, 108018.

Assessing how climate factors regulate the interannual variability (IAV) of ecosystem productivity globally is crucial for understanding the ecosystem-climate interactions and carbon-climate feedbacks under a changing climate. However, our understanding of global climatic controls on the IAV of ecosystem productivity has been limited by the lack of direct measurements of ecosystem productivity at the global scale. We used a long-term, fine-resolution solar-induced chlorophyll fluorescence (SIF) product (GOSIF) derived from SIF soundings measured by the Orbiting Carbon Observatory-2 (OCO-2) to investigate how climatic factors drive the IAV of global ecosystem productivity. We also examined how the results derived from SIF differed from those based on a satellite-derived measure of vegetation greenness and productivity - the enhanced vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). Both productivity measures showed the dominant role of soil moisture in driving the IAV of global ecosystem productivity, particularly in arid and semi-arid areas. SIF was more sensitive to climate variability than was EVI. SIF was positively correlated with solar radiation in the humid regions, while no significant correlations were found between EVI and solar radiation. The stronger correlation of SIF with climate factors was also observed at the ecosystem level based on a number of eddy covariance flux sites, indicating that SIF had a higher ability in capturing the variations of gross primary productivity (GPP) than did EVI. The comparison between SIF and EVI also highlighted the biome-specific (depending on the tree cover) responses of ecosystem productivity to solar radiation under water stress. Our findings explicitly reveal the global climatic controls on the IAV of ecosystem productivity, and provide insight into the mechanistic differences between SIF and vegetation indices in characterizing ecosystem productivity.