Divergent responses of bacterial communities to permafrost degradation and their roles in mediating carbon across vertical profile

Permafrost degradation poses a significant threat to the organic carbon (C) pool primarily through regulating microorganisms. However, microbial responses and their associations with C loss across vertical profile remain unclear. Here, we used metagenomic sequencing to investigate bacterial communities in 125 samples from five 15 m-depth permafrost cores, spanning from the active layer to the permafrost layer along a degraded gradient on the Qinghai-Tibet Plateau. We find that α-diversity decreases, while stochastic processes and community stability increase from the active layer to the permafrost layer. Along permafrost degradation, these community attributes follow similar variations within the active layer but remain basically constant within the permafrost layer. The relative abundance and interaction of core taxa play important roles in maintaining community stability in the active and permafrost layers, respectively. Interestingly, degradation strengthens the negative effect of community stability on C storage, with this link being stronger in the active layer than the permafrost layer, further exacerbating C loss. Our findings provide novel insights into the capacity of microbial-mediated permafrost C sequestration and contribute to modeling C dynamic under future warming.