Carbon-Degrading Gene Resistance Contributes to Microbial Thermal Adaptation of Soil Carbon Decomposition

The thermal adaptation of the microbial community can potentially mitigate the positive feedback between soil carbon loss and climate change. However, the mechanistic basis of this process remains unclear, particularly the link between functional genes and microbial metabolic physiology in regulating the thermal response of soil carbon decomposition. While most experimental warming studies have examined elevated mean temperatures, the magnitude of temperature fluctuations is also increasing under climate change and may impose distinct ecological effects on microbial processes. This knowledge gap likely underlies current uncertainties in predicting microbial contributions to soil carbon-climate feedbacks. Here, we conducted a 200-day incubation with soil samples from six subtropical forests spanning a 2000 km transect in China under two climate change scenarios: elevated mean temperature and increased temperature fluctuation. We found that the stronger functional gene resistance governed the thermal adaptation of the maximum potential reaction rate (V_max, an indicator of microbial decomposition of soil carbon) of three carbon-degrading enzymes under increased temperature fluctuation, while the enhancing response of V_max under elevated mean temperature was driven by the attenuated microbial community resistance. These findings provide a mechanistic basis for predicting microbially mediated feedbacks between soil carbon and temperature change via microbial physiology, offering empirical evidence for integrating microbial processes into Earth system models under climate warming.