Resilience mechanisms in soil organic carbon storage after pre-commercial thinning in mixed oak-pine forests

Microbial communities are essential for soil organic matter decomposition and regulate soil carbon dynamics. However, the microbial mechanisms through which thinning restoration processes regulate soil organic carbon (SOC) storage remain unclear. To elucidate how thinning influences SOC storage through microbial processes, we employed Illumina sequencing and ecoenzymatic stoichiometry to analyze microbial communities, soil enzymes, microbial element limitations, and microbial carbon use efficiency (CUE) across a thinning chronosequence (CK: no thinning, T2018: thinned ∼4 years prior, and T2010: thinned ∼12 years prior). Thinning significantly altered keystone fungal community composition. The relative abundance of Ascomycota decreased following thinning and was significantly lower in T2010 than in CK. In contrast, the relative abundance of Basidiomycota decreased in T2018 but increased in T2010 and was significantly higher than in T2018. Microbial metabolism shifted from phosphorus limitation to combined carbon-phosphorus limitation following thinning. Carbon limitation intensified in T2018 but was alleviated in T2010, and it persisted even when SOC stocks recovered to pre-thinning levels. SOC stocks in T2018 were 44.81 % lower than in CK but recovered in T2010 to levels comparable with CK (showing a 43.27 % increase relative to T2018). Furthermore, post-thinning changes in SOC stocks were driven by shifts in microbial CUE and the relative abundance of keystone fungal taxa, with microbial CUE regulated by soil water content (SWC) and microbial element limitations, whereas the relative abundance of keystone fungal taxa was regulated by SWC. This study elucidates mechanisms driving post-thinning SOC storage recovery and informs forest management to enhance soil carbon sequestration.