Soil moisture deficits amplify and prolong vegetation productivity losses under compound dry-hot extremes

Compound dry-hot extremes have emerged as a major threat to terrestrial ecosystem productivity under climate change, yet their impacts are commonly interpreted through atmospheric conditions alone. Here we distinguish between compound meteorological dry-hot (CMDH) events, driven by atmospheric dryness and heat, and compound soil dry-hot (CSDH) events, in which soil moisture deficits coincide with heat, and assess their differential effects on global vegetation productivity. Integrating multiple gross primary productivity (GPP) datasets with climate variables, we quantify GPP loss and recovery time following CMDH and CSDH events. Globally, CSDH causes deeper productivity losses than CMDH, with a mean additional reduction of 1.115 g·C·m-2·day-1, and prolongs recovery by 2.238 days on average. These differences have intensified over recent decades, with CSDH-related GPP losses and recovery times diverging increasingly from CMDH. The dominance of soil-driven impacts is also shown to strengthen with event severity, climate aridity, and under future warming scenarios. Structural equation modeling and explainable machine learning further reveal a shift in controlling mechanisms from atmospheric demand under CMDH to soil moisture limitation under CSDH, explaining both deeper carbon losses and longer ecosystem memory. Our results demonstrate that soil-coupled compound dry-hot extremes exert a more persistent constraint on terrestrial productivity than atmospheric counterparts, highlighting soil moisture as a critical regulator of ecosystem resilience in a warming world.