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 has often been modeled as an exponential function of temperature, recent evidence shows that ER exhibits an optimal temperature (T _opt ) and a monotonic response beyond this threshold. 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 five years of observation. Our results show that T _opt of ER increased with rising temperatures, indicating thermal acclimation, with a global average acclimation magnitude (T _opt change per unit change in maximum temperature across years within the site) of 0.82°C. More interestingly, this acclimation magnitude showed a negative correlation with mean annual temperature. This negative correlation suggests that ecosystems in colder regions exhibit higher acclimation magnitudes compared to warmer regions, potentially reducing the variation in T _opt across biomes under future warming. These findings indicate a homogenization of T _opt under warming conditions. Our scenario analysis suggested that neglecting thermal acclimation may lead to inaccurate T _opt estimates under future climate scenarios, underscoring the need to incorporate variable thermal acclimation responses of T _opt into Earth System Models.