Decoupling of soil carbon mineralization and microbial community composition across a climate gradient on the Tibetan Plateau

Abstract

Soil microbes drive soil organic carbon (SOC) mineralization. Because microbial groups differ in metabolic efficiency and respond differently to temperature variation, it is reasonable to expect a close association of SOC mineralization and its temperature sensitivity (Q10 which is defined as the factor of the change of soil carbon mineralization induced by 10 °C temperature increase) with microbial community diversity and composition. However, these relations have rarely been tested. Here, we conducted an incubation experiment to assess the temperature responses of microbial α diversity and the relative abundance of microbial r- and K-strategists in soils from a wide range of ecosystems across a climate gradient in the southeast Tibet. The results indicated that the instantaneous α diversity and the relative abundance of r- and K-strategists are significantly (P < 0.05) influenced by temperature, but these microbial variables are poor predictors of SOC mineralization measured at the same time. Rather, microbial community diversity and the relative abundance of r- and K-strategists of fresh soils showed consistent and significant (P < 0.05) effects on both SOC mineralization and Q10 at different incubation stages. Importantly, path analysis indicated that microbial α diversity and r- and K-strategists exerts no independent effects on SOC mineralization and Q10 when variation in climate, SOC chemistry, physical protection, and edaphic properties are accounted for. Together, our results suggest that while soil microbial community diversity and composition are a strong proxy of SOC quality and availability, they are not a fundamental determinant of SOC mineralization and Q10.