A temperature threshold to identify the driving forces of the respiratory process in terrestrial ecosystems

Terrestrial ecosystem respiration (Re) is the major source of CO2 release and constitutes the second largest carbon flux between the biosphere and atmosphere. Therefore, changes of Re should greatly impact on the global carbon cycle. The aim of this study was to derive an air temperature threshold to identify the driving forces of the respiratory process in terrestrial ecosystems within different temperature zones. A dataset of 647 site-years of ecosystem flux data was collected at 152 sites globally. Based on analyses of the dataset, an ecological threshold of mean annual air temperature (MAT) (i.e., 11±2.3?) was identified. In ecosystems with the MAT below the threshold, the maximum Re rates were primarily dependent on temperature and respiration was mainly a temperature-driven process. In ecosystems with the MAT greater than 11±2.3?, besides temperature, other driving forces, such as water availability and heat flux, became significant to affect the maximum Re rates and respiration was a multi-factor-driven process. The global scale analysis indicate that the driving force of temperature controls the maximum Re rates in most of terrestrial ecosystems, while other driving forces reduce the maximum Re rates and temperature sensitivity of the respiratory process. Information from this study might play an important role for reliable assessment of the global carbon processes.