Evidence for widespread thermal optimality of ecosystem respiration

Ecosystem respiration (ER) is among the largest carbon fluxes between the biosphere and the atmosphere. Understanding the temperature response of ER is crucial for predicting the climate change–carbon cycle feedback. However, whether there is an apparent optimum temperature of ER ( T_opt^ ER ) and how it changes with temperature remain poorly understood. Here we analyse the temperature response curves of ER at 212 sites from global FLUXNET. We find that ER at 183 sites shows parabolic temperature response curves and T_opt^ ER at which ER reaches the maximum exists widely across biomes around the globe. Among the 15 biotic and abiotic variables examined, T_opt^ ER is mostly related to the optimum temperature of gross primary production (GPP, T_opt^ GPP ) and annual maximum daily temperature ( T max ). In addition, T_opt^ ER linearly increases with T max across sites and over vegetation types, suggesting its thermal adaptation. The adaptation magnitude of T_opt^ ER , which is measured by the change in T_opt^ ER per unit change in T max , is positively correlated with the adaptation magnitude of T_opt^ GPP . This study provides evidence of the widespread existence of T_opt^ ER and its thermal adaptation with T max across different biomes around the globe. Our findings suggest that carbon cycle models that consider the existence of T_opt^ ER and its adaptation have the potential to more realistically predict terrestrial carbon sequestration in a world with changing climate.