Microbial mechanism on the turnover of soil organic carbon responded to litter C:N ratio and incubation temperature

Background and aims Soil organic carbon (SOC) turnover is closely linked to global carbon cycling, yet the microbial mechanisms underlying its response to warming and litter quality remain poorly understood. Therefore, this study aimed to explore the bacterial mechanisms driving SOC turnover in response to different incubation temperature and litter C:N ratio. Methods Here, a one-year incubation experiment was conducted with three types of ¹³C-labeled litter differing in C:N ratio (11.66, 27.77, and 35.81) under two incubation temperatures (23°C and 33°C). At the end of incubation, the soil properties were measured, and soil bacterial community properties were examined using the Illumina MiSeq sequencing method. Results SOC turnover was maximized, and SOC half-life minimized, under the medium C:N litter (27.77), indicating that a C:N ratio close to microbial demand favors carbon transformation. Warming significantly accelerated SOC turnover, particularly with medium and high C:N litter additions. Bacterial α-diversity increased with medium C:N litter but declined with warming. Elevated temperature reduced the abundance of copiotrophic taxa (e.g., Proteobacteria) and enhanced oligotrophic groups (e.g., Firmicutes). Path modeling revealed that DOC and pH positively, but available nitrogen negatively, regulated the incorporation of newly derived carbon into SOC. Conclusions Our findings highlight that SOC turnover is jointly controlled by litter quality and warming, with temperature exerting a stronger influence on bacterial communities. This study provides new insights into the microbial mechanisms linking substrate quality, warming, and SOC stability, with implications for predicting soil carbon dynamics under future climate change.