Soil moisture thresholds for the temperature sensitivity of ecosystem respiration

Ecosystem respiration (ER) is the largest source of biogenic CO₂ to the atmosphere, and its temperature sensitivity (Q₁₀) is key to land–climate feedback. However, despite decades of studies finding that Q₁₀ varies considerably across space, time, and biomes, the drivers controlling this variation remain unclear. Here we show that Q₁₀ variability of can be unified within a common hydrothermal framework. Using data from 142 eddy covariance sites around the world, we reveal that Q₁₀ exhibits unimodal responses to soil moisture. At each site, Q₁₀ first increases with soil moisture, peaks at a threshold (SMₜₕ), and then declines. This SM_th is ecosystem-specific, which emerges from coordinated plant–soil–microbial interactions, shaped by long-term hydroclimatic regimes and soil physical constraints. Global mapping of SMₜₕ shows that about 25% of the planet’s vegetated land currently has a soil moisture level that exceeds SMₜₕ, including many carbon-rich peatlands and tropical forests, where moderate drying could enhance temperature sensitivity and carbon loss. Our findings establish that moisture thresholds offer an ecological framework that unifies the regulation of carbon fluxes through water and heat. Incorporating this framework into Earth system models will fundamentally improve predictions of carbon–climate feedback under accelerating hydroclimatic change.