Air and surface temperatures differently drive terrestrial carbon and water cycles in the high latitudes

High-latitude vegetation can experience much higher surface temperatures (T _surf , at radiative equilibrium) than the ambient air temperature (T _air ). In snow-free seasons, T _surf is closely linked to plant physiological and biochemical processes. We drove the dynamic ecosystem model LPJ-GUESS with reanalysis data ERA5-land T _surf and 2-m T _air to understand regional responses to these two temperatures. We show that plant growth in the tundra is stimulated by warmer T _surf in the summer months, but in the boreal forests, colder T _surf in the non-summer months constrains leaf development and enzyme activity for the growing season. T _surf drives higher primary productivity of tundra plant individuals, but in the boreal forests, productivity is co-influenced by less productive individuals and compensatory changes in vegetation structure (coverage and density). This study demonstrates the importance of forcing temperature in simulating high-latitude ecosystem processes and calls for using correct plant-experienced temperatures to reduce uncertainties in estimating responses and feedback to the climate.