Bacterial community composition changes independently of soil edaphic parameters with permafrost disturbance

Abstract. Microbial degradation of frozen organic carbon increases with permafrost thaw, resulting in greater fluxes of the greenhouse gases CO₂ and CH₄. To examine the effect of disturbance-induced permafrost thaw on microbial communities, we assessed the microbial diversity of soils near a gold mine where thaw was induced by stripping the vegetation and topsoil at Dominion Creek, Yukon, Canada. Bacterial metabarcoding and soil physicochemical parameters were assessed across this disturbance including surface samples and three cores which included active layer and permafrost horizons. Bacterial communities changed in the absence of physicochemical parameter shifts after only 6 weeks of thaw, with a high proportion of active layer indicator species becoming more abundant with permafrost thaw. Three distinct communities emerged: (1) undisturbed active layer, (2) lower active layer, disturbed active layer, and disturbed permafrost samples, and (3) intact permafrost. Community composition shifts correlated with pH, Zn and community cohesion. These results suggest that active layer communities rapidly colonize thawed permafrost, combining with and replacing many resident permafrost taxa. Disturbances may induce a strong microbial community change in permafrost-affected soils before soil physicochemical parameter shifts.