Asynchrony of the seasonal dynamics of gross primary productivity and ecosystem respiration

Phenological cycles of plants have changed with changing climate, and the altered biogeochemical fluxes may exert feedbacks on the climate system. As regulators of land carbon balance and the counterbalance to anthropogenic carbon emissions, the phenology of gross primary productivity (GPP) and ecosystem respiration (RE) and their trends under climate change are of great importance from carbon cycling and carbon sequestration perspective. While the environmental controls of GPP and RE are well understood, the interannual variability of their seasonal dynamics remain poorly constrained. Yet, they determine a large part of carbon exchange and carbon cycle-climate feedback. Even less is known about the consistency of temporal synchrony between GPP and RE phenology, or how this relationship varies among different functional traits. In this study, we examined change trends of GPP and RE phenology and quantify the resulting changes in net ecosystem carbon balance using the global Flux Seasonality Metrics Database (FSMD) derived from FLUXNET 2015 dataset. We found that GPP and RE diverged both in terms of the flux seasonality metrics and interannual trends. Consistent with earlier reports, we observed that GPP is more sensitive than RE to changes in spring temperature and less sensitive than RE to fall temperature. Yet, the extension of the growing season in both spring and fall increased GPP more than it did RE.