Thermal adaptation of net ecosystem exchange

Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland ecosystems located at latitudes ranging from ∼29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (T_b) at which ecosystem transfer from carbon source to sink and optimal temperature (T_o) at which carbon uptake is maximized. T_b was strongly correlated with annual mean air temperature. T_o was strongly correlated with mean temperature during the net carbon uptake period across the study ecosystems. Our results imply that the net ecosystem exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and ecosystem respiration.