Spatial Differentiation and Community Assembly of Soil Bacterial Communities in Permafrost Peatlands of the Greater Khingan Mountains

Global warming is profoundly altering the structure and function of permafrost peatland ecosystems, but how soil microorganisms as core regulators of biogeochemical cycles respond to the process remains unclear. We investigated peatlands of the continuous, the discontinuous, and the isolated permafrost zones in the climatically sensitive high-latitude Greater Khingan Mountains using 16S rRNA gene high-throughput sequencing and soil physicochemical analysis to systematically reveal the spatial differentiation patterns, community assembly processes, and primary environmental factors of bacterial communities. The results indicated that bacterial alpha diversity was highest in the discontinuous permafrost zone, and both permafrost type and soil depth exerted significant effects on bacterial community composition. From the continuous to the isolated permafrost zones, the relative abundance of the dominant phylum Proteobacteria decreased, while phylum Chloroflexota showed a gradual increasing trend. Co-occurrence network analysis suggested that bacterial network complexity was highest in the continuous permafrost zone, and network stability decreased along the permafrost gradient. From the continuous to the isolated permafrost zone, the relative contribution of stochastic processes declined, whereas that of deterministic processes increased. Partial least squares path modeling (PLS-PM) further demonstrated that soil pH, total organic carbon (TOC), total nitrogen (TN), and soil water content (SWC) were major drivers of bacterial communities, with their effects differing among permafrost zones. Our study elucidated the synergistic evolutionary patterns of bacterial community composition, assembly mechanisms, and environmental drivers under permafrost degradation, providing key scientific evidence for predicting the feedback of high-latitude peatlands to climate warming.