The Optimal Temperature of Ecosystem Respiration Homogenizes Under Global Warming

Terrestrial ecosystem respiration (ER) is a key component of the carbon cycle and is highly temperature sensitive. While ER is often modeled as an exponential function of temperature, recent evidence shows that ER exhibits an optimal temperature (T_opt). However, the temporal dynamics of T_opt under climate warming remain poorly understood. This study analyzed data from 135 long-term FLUXNET sites, each with at least 5 years of observation. Our results show that T_opt of ER increased with rising temperatures across years within a site, indicating thermal acclimation, with a global average acclimation magnitude (T_opt change per unit change in maximum temperature) of 0.82. More interestingly, this acclimation magnitude showed a negative correlation with the mean annual temperature across sites which was particularly evident in deciduous broadleaf forests and in cold regions. This negative correlation suggests that ecosystems in colder sites exhibit higher acclimation magnitudes compared to warmer sites, potentially reducing the variation in T_opt across globe under future warming. These findings indicate a global homogenization of T_opt under warming conditions. Future scenario analysis suggested that neglecting thermal acclimation may lead to inaccurate T_opt estimates under climate change. This study underscores the importance of considering variable thermal acclimation responses of T_opt for accurate prediction of future ER.