Diverse Coupling/Decoupling Patterns Between Photosynthesis and Evapotranspiration Among Various Ecosystems

Photosynthesis (quantified as gross primary productivity, GPP) and evapotransporation (ET) represent carbon and water fluxes of terrestrial ecosystems and play influential roles in climate change. Several studies have found the long-term global trends of increasing GPP and ET primarily driven by CO2 fertilization and increasing land temperature over the past two decades. These trends would evolve with the interaction between these terrestrial processes and climate change. A better prediction of these evolutionary trends is essential for terrestrial ecosystem management to face the challenges of future climate change, but requires a mechanistic understanding of how GPP, ET, and their relationship respond to various environmental drivers. Among many mechanistic questions, the complex dynamics of GPP-ET coupling/decoupling related to stomatal regulation on GPP and transpiration (T) and the effects of driving environmental factors on GPP, T, and evaporation (E) are less explored relative to the dynamics of individual processes. In this study, we attempted to address the two questions based on the FLUXNET 2015 database: (1) How do the GPP-ET coupling/decoupling patterns differ across various ecosystems? (2) How do the diverse GPP-ET coupling/decoupling patterns attribute to the different responses of GPP, T, and E to environmental drivers? Preliminary results indicated that short-term GPP-ET coupling is stronger in forests than in grasslands and shrublands. In contrast, the long-term pattern might be the opposite, with a more significant decoupling in forests. Further analysis will partition the contributions of GPP, E, and T components to the GPP-ET coupling/decoupling patterns in various ecosystems.