Dryness controls temperature-optimized gross primary productivity across vegetation types

Temperature response of gross primary productivity (GPP) is a well-known property of ecosystem, but GPP at the optimum temperature (GPP_T-opt) has not been fully discussed. Our understanding of how GPP_T(opt )responds to warming and water availability is highly limited. In this study, we analyzed data at 326 globally distributed eddy covariance sites (79(o)N-37(o)S), to identify controlling factors of GPP_Topt. Although GPP_Topt was significantly influenced by soil moisture, global solar radiation, mean annual temperature, and vapor pressure deficit in a non-linear pattern (R-2 = 0.47), the direction and magnitude of these climate variables' effects on GPP_T-opt depend on the dryness index (DI), a ratio of potential evapotranspiration to precipitation. The spatial pattern showed that soil moisture did not affect GPP_T(opt )across energy-limited sites with DI < 1 while dominated GPP_T-opt across water-limited sites with DI > 1. The temporal pattern showed that GPP_T-opt was lowered by warming or low precipitation in water-limited sites while energy-limited sites tended to maintain a stable GPP_T-opt regardless of changes in air temperature. Vegetation types in humid climates tended to have higher GPP_T(opt )and were more likely to benefit from a warmer climate since it was not restricted by water conditions. This study highlights that the response of GPP_T-opt to global warming depends on the dryness conditions, which explains the nonlinear control of water and temperature over GPP_T-opt. Our finding is essential to realistic prediction of terrestrial carbon uptake under future climate and vegetation conditions.

Automated summary

This study analyzed data from 326 globally distributed sites and found that GPP_T_opt responds non-linearly to climate variables such as soil moisture, solar radiation, temperature, and vapor pressure deficit. The response of GPP_T_opt to global warming depends on the dryness conditions, with vegetation in humid climates benefiting more from a warmer climate.