Predicting the temperature dependence of microbial respiration in soil: A continental-scale analysis

The production of CO₂ by soil microorganisms is an important component of the global carbon cycle, and its temperature sensitivity is poorly constrained in global models. To improve our understanding of the factors controlling the temperature dependence of soil microbial respiration, we analyzed the temperature sensitivity of labile soil organic carbon decomposition for 77 soils collected from a wide array of ecosystem types. Across all of the soils, the average Q₁₀ value (the factor by which decomposition rates increase for a 10°C increase in temperature) was 3.0, but the range in Q₁₀ values was substantial (2.2 to 4.6). A large percentage (45%) of the variation in Q₁₀ values could be explained by the relative rate of microbial respiration per unit organic C, an analog for C quality. This result provides support for the "carbon quality-temperature" hypothesis that directly links the temperature dependence of microbial decomposition and the biochemical recalcitrance of soil organic carbon. A smaller percentage (17%) of the variability in Q₁₀ values could be explained by the mean monthly temperature at the time of sampling, suggesting that microbial communities may adapt to the antecedent temperature regime. By showing that the Q₁₀ of microbial respiration in soil is largely predictable under standardized incubation conditions, this work increases our understanding of the temperature sensitivity of labile soil organic carbon stores.