THE SENSITIVITY OF SOIL RESPIRATION TO SOIL TEMPERATURE, MOISTURE, AND CARBON SUPPLY AT THE GLOBAL SCALE

Soil respiration is one of the most important terms in the global carbon budget, yet we know very little about how important environmental factors control this process at the global scale. Soils contain more carbon than terrestrial biomass and the atmosphere combined and contribute ten times more carbon dioxide to the atmosphere each year than the burning of fossil fuels. This study provides new insight on the factors driving soil respiration at the global scale by assimilating satellite observations of soil moisture, temperature, and net primary productivity with the Global Soil Respiration Database (SRDB).While temperature, moisture, carbon supply and other site characteristics are known to regulate soil respiration rates at the plot scale within certain biomes, there is no quantitative framework for evaluating the relative importance of these factors across different biomes and at the global scale. We link a subset of observations in the SRDB to soil moisture, soil temperature, net primary productivity (NPP), and soil carbon from global datasets in order to explore the relative strengths of these environmental regulators on soil respiration. We find that calibrating models with parabolic soil moisture functions can improve predictive power over similar models with asymptotic functions of mean annual precipitation. At the global scale, soil temperature is the dominant factor regulating soil respiration; however, soil moisture emerges as the dominant factor regulating soil respiration in temperate and boreal forested ecosystems, and NPP emerges as the dominant factor regulating soil respiration in croplands and grasslands dominated ecosystems. We compare the ways in which these statistical relationships predict global soil respiration values in generalized additive models and several calibrated models with mechanistic structures, which estimate total respiration fluxes ranging from 83 to 108 Pg/yr