Temperature responses of ecosystem respiration

Terrestrial ecosystems release ~106–130 PgC yr^–1 into the atmosphere through respiration, counterbalancing photosynthetic carbon uptake and determining the strength of the land carbon sink. The effect of anthropogenic warming on the land carbon sink will depend on the temperature response of respiration. In this Review, we explore the relationships between temperature and ecosystem respiration from experimental and observational data at leaf, microbial, ecosystem and global scales. Contrary to the assumed monotonic increase in respiration with increasing temperature derived from Earth system models, empirical findings indicate a unimodal temperature response with a peak in respiration at an optimal temperature (T_opt). This unimodality is observed across a range of organization levels with T_opt values of 40–60 °C at the leaf and plant level, 11–46 °C at a microbial level and 6.5–33.3 °C at the global scale. Various mechanisms contribute to this unimodal pattern including enzyme deactivation, the thermodynamics of enzyme-catalysed reactions and changes in temperature-dependent factors such as soil moisture, nutrient availability and vegetation physiology. Incorporating the unimodality of these observed temperature responses of ecosystem respiration into Earth system models could facilitate attribution studies to identify the mechanisms responsible for the peaked response and increase the accuracy of carbon sequestration predictions.