Global warming leads to the melting of permafrost, affects changes in soil microbial community structures and related functions, and contributes to the soil carbon cycle in permafrost areas. Located at the southern edge of Eurasia's permafrost region, the Greater Khingan Mountains are very sensitive to climate change. Therefore, by analyzing the bacterial community structure, diversity characteristics, and driving factors of soil profiles (active surface layer, active deep layer, transition layer, and permafrost layer) in this discontinuous permafrost region, this research provides support for the study of the carbon cycling process in permafrost regions. The results show that the microbial diversity (Shannon index (4.81)) was the highest at 0-20 cm, and the Shannon index of the surface soil of the active layer was significantly higher than that of the other soil layers. Acidobacteria and Proteobacteria were the dominant bacteria in the active layer soil of the permafrost area, and Chloroflexi, Actinobacteria, and Firmicutes were the dominant bacteria in the permafrost layer. Chloroflexi made the greatest contribution to the bacterial community in the permafrost soil, and Bacteroidota made the greatest contribution to the bacterial community in the active surface soil. The structure, richness, and diversity of the soil bacterial community significantly differed between the active layer and the permafrost layer. The number of bacterial species was the highest in the active layer surface soil and the active layer bottom soil. The difference in the structure of the bacterial community in the permafrost soil was mainly caused by changes in electrical conductivity and soil-water content, while that in the active layer soil was mainly affected by pH and soil nutrient indices. Soil temperature, NO3--N, and pH had significant effects on the structure of the bacterial community. The active layer and permafrost soils were susceptible to environmental information processing and genetic information processing. Infectious disease: the number of bacterial species was significantly higher in the surface and permafrost layers than in the other layers of the soil. In conclusion, changes in the microbial community structure in soil profiles in discontinuous permafrost areas sensitive to climate change are the key to soil carbon cycle research.

Soil microorganisms are crucial contributors to the function of permafrost ecosystems, as well as the regulation of biogeochemical cycles. However, little is known about the distribution patterns and drivers of high-latitude permafrost microbial communities subject to climate change and human activities. In this study, the vertical distribution patterns of soil bacterial communities in the Greater Khingan Mountain permafrost region were systematically analyzed via Illumina Miseq high-throughput sequencing. Bacterial diversity in the active layer was significantly higher than in the permafrost layer. Principal coordinate analysis (PCoA) indicated that the bacterial community structure in the active layer and the permafrost layer was completely separated. Permutational multivariate analysis of variance (PERMANOVA) detected statistically significant differentiation across the different depths. The relative abundance of the dominant phyla Chloroflexi (17.92%-52.79%) and Actinobacteria (6.34%-34.52%) was significantly higher in the permafrost layer than in the active layer, whereas that of Acidobacteria (4.98%-38.82%) exhibited the opposite trend, and the abundance of Proteobacteria (2.49%-22.51%) generally decreased with depth. More importantly, the abundance of bacteria linked to human infectious diseases was significantly higher in the permafrost layer according to Tax4Fun prediction analysis. Redundancy analysis (RDA) showed that ammonium nitrogen (NH4+-N), total organic carbon (TOC), and total phosphorus (TP) were major factors affecting the bacterial community composition. Collectively, our findings provide insights into the soil bacterial vertical distribution patterns and major environmental drivers in high-latitude permafrost regions, which is key to grasping the response of cold region ecosystem processes to global climate changes.

The rapid permafrost degradation caused by climate warming can lead to thermokarst development, which in turn greatly alter soil parameters and impact the soil bacterial communities. However, the effects of thermokarst development on soil bacterial communities largely remain unclear. Here we selected a typical thaw slump in the Qinghai-Tibet Plateau. We classified three microfeatures in the thaw slump areas, i.e., control, slumping and exposed and collected surface 30 cm soils at a depth interval of 10 cm using a soil auger. The results showed that thaw slump decreased soil carbon and nitrogen contents especially for the topsoil (0-10 cm). Thaw slump increased the relative abundance of Gemmatimonadaceae, but decreased the relative abundance of Micrococcaceae. The richness indices including OTU numbers, Ace, Chao 1 and Simpson indices were the largest in the exposed area and lowest in the slumped area, and these trends were opposite to the Shannon index. Correlation analysis revealed that the relative abundance of Micrococcaceae was negatively correlated with moisture, Anaerolineaceae was positively correlated with organic carbon content. The Nitrospira, RB41 and Gemmatimonadaceae were negatively associated with total nitrogen, but Anaerolineaceae and JG30-KF-CM45 were positivity correlated with total nitrogen. C/N ratio was positively correlated with RB41 but negatively correlated with JG30-KF-CM45. We concluded that soil organic carbon, total nitrogen and C/N ratio were the most important factors shaping the bacterial community structure among the three microfeatures. The bacterial community diversity was the highest in the exposed area and lowest in the slumping area. The bacterial structure community was related with total nitrogen, soil organic carbon contents and C/N ratios. Overall, our findings showed thaw slump can decrease soil organic carbon and nitrogen content for the surface soils in the alpine meadow and further change the soil bacterial communities.