Seasonal increases in global dryland gross primary production are modulated by root soil moisture and temperature

Dryland ecosystems, which are highly sensitive to environmental variability across space and through time, play a critical role in the global carbon cycle. To understand the carbon sink role of drylands, this study used different sources of global dryland gross primary productivity (GPP) and evaluated the spatiotemporal variations in seasonal GPP in response to climatic and soil water conditions from 1982 to 2018. Root-zone soil moisture consistently exerted a predominant positive influence on dryland GPP across all seasons, while the effect of surface soil moisture was less influential. Maximum temperature (Tmax) ranked as the second most influential factor on GPP, switching from a notable positive effect during cooler seasons to a negative impact during warmer seasons. Similarly, during cool seasons, vapor pressure deficit exhibited a notable positive effect on GPP, but this influence became negative in warmer seasons. Tmax indirectly regulated GPP by modulating the influence of other meteorological factors. During the warm season, Tmax negatively affected GPP via VPD, while in the cold season, it positively affected GPP through VPD. This study explicitly identifies the pivotal role of root-zone soil moisture in determining GPP and highlights the substantial seasonal differences and regulatory role of temperature in how other environmental variables influence GPP. These findings provide a novel perspective for understanding the responses of dryland ecosystems to climate change.