Evidence for widespread thermal optimality of ecosystem respiration

Abstract

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 ( $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ ) 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 $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ at which ER reaches the maximum exists widely across biomes around the globe. Among the 15 biotic and abiotic variables examined, $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ is mostly related to the optimum temperature of gross primary production (GPP, $${{T}}_{{\rm{opt}}}^{\,{\rm{GPP}}}$$ ) and annual maximum daily temperature (Tmax). In addition, $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ linearly increases with Tmax across sites and over vegetation types, suggesting its thermal adaptation. The adaptation magnitude of $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ , which is measured by the change in $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ per unit change in Tmax, is positively correlated with the adaptation magnitude of $${{T}}_{{\rm{opt}}}^{\,{\rm{GPP}}}$$ . This study provides evidence of the widespread existence of $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ and its thermal adaptation with Tmax across different biomes around the globe. Our findings suggest that carbon cycle models that consider the existence of $${{T}}_{{\rm{opt}}}^{\,{\rm{ER}}}$$ and its adaptation have the potential to more realistically predict terrestrial carbon sequestration in a world with changing climate. Temperature response curves of ecosystem respiration from 212 globally distributed sites show widespread evidence for an optimum temperature that is the result of thermal adaptation.