Temperature constraints of terrestrial ecosystem respiration in global biomes

Ecosystem respiration (Re) plays a critical role in the global carbon cycle, but is conventionally modelled with temperature response functions that do not adequately account for the limiting effects of high temperature on Re. Using Re data from the FLUXNET2015 network, we compared the conventional exponential temperature response function with a unimodal function that incorporates these effects. We found that the conventional function significantly underestimates the sensitivity of Re to temperature, potentially leading to overestimation of future carbon emissions. The activation energy (Ea) estimated by the unimodal function averaged 0.97 ± 0.44 eV, substantially higher than the 0.58 ± 0.27 eV calculated by the exponential function. The temperature threshold (Tth) for Re inhibition was identified at an average of 26.58°C across biomes. The largest Re increase occurs under SSP585, reaching 147.85% and 153.81% for the exponential and unimodal functions, respectively, by 2100 relative to Re simulated using the exponential function in 1990. As rising temperatures push ecosystems toward their thermal optimum, greater overestimation beyond the divergence threshold in SSP585 reduces the difference between the two functions compared to SSP245 and SSP370. These findings emphasize an underestimated temperature dependence and inaccurate trends in ecosystem respiration, highlighting the necessity of integrating high-temperature inhibition effects into Re models to improve projections of carbon dynamics.