Transpiration Changes With Soil Warming: Insights From a Mechanistic Model

Abstract Transpiration (T) connects water, energy, and carbon cycles within ecosystems. While T has often been reported to increase with soil warming, underlying reasons remain poorly understood. Here, using a mechanistic ecohydrological model, T&C‐BG, we simulated T responses to soil warming at 30 sites spanning various biomes and climates. Consistent with observations, the numerical model reproduces negative, insignificant, and predominantly positive T responses under soil warming. Numerical results show that soil warming generally increases T for sites with a small Bowen ratio. The main mechanisms leading to positive T responses to soil warming are complex changes in energy partitioning with modifications of canopy surface temperature and aerodynamic, stomatal, and leaf boundary layer conductance. However, soil warming can also affect phenology, which might result in either increased or decreased T. Our findings shed light on how T changes with warmer soil and help interpret outcomes of warming experiments.