Air and Surface Temperatures Differently Drive Terrestrial Carbon and Water Cycles in the High Latitudes

High-latitude vegetation experience different temperatures than the ambient air temperature. While lacking a regional plant temperature product, we drove the dynamic ecosystem model, LPJ-GUESS, with widely used ERA5-land surface temperature (T_surf, at radiative equilibrium) and air temperature to understand ecosystem process responses to these two temperatures. We show that tundra plants' growth is stimulated by warmer T_surf in the summer, but in the boreal forests, colder T_surf in the non-summer months constrains leaf development and enzyme activity the following growing season. T_surf drives higher productivity of tundra plant individuals but leads to less productive individuals in the boreal forest, although with compensatory changes (almost 68%) in vegetation structure. We demonstrate the importance of forcing temperature in simulating high-latitude ecosystem processes and call for a community effort to measure plant temperatures across canopy heights and seasons to reduce uncertainties in estimating high-latitude plant responses and feedback to climate.