Changes in soil bacterial community along a gradient of permafrost degradation in Northeast China

Spatial fragmentation of permafrost alters soil hydrothermal conditions and physicochemical properties that control microbial activity responsible for the decomposition of organic matter. Due to climate warming, there is a need to identify changes in microbial community and diversity to predict altered soil function along permafrost degradation gradient. To determine the drivers of soil bacterial community at regional (across permafrost regions) and local scales (across habitats, within permafrost region), the method of “space instead of time” was adopted. The soil samples were collected from forest and wetland ecosystems in three types of west-east permafrost regions (including discontinuous, sporadic and isolated patches permafrost regions, which represent the primary degenerate sequence) in Northeast China. The results showed that Chloroflexi, Proteobacteria, Actinobacteria, and Acidobacteria were the most abundant phyla. The effect of permafrost degradation on bacterial relative abundance varied by species and habitats. The response of soil bacterial α-diversity (the observed OTU richness and phylogenetic diversity) in forests and wetlands to permafrost degradation were inconsistent. It was significantly correlated with mean annual temperature (MAT), mean annual precipitation (MAP), soil pH, soil microbial biomass carbon (MBC) and nitrogen (MBN) contents. The structure of soil bacterial community became increasingly dissimilar with degradation, indicating that permafrost degradation significantly changed the bacterial community structure. Climate conditions and edaphic factors jointly contribute to 92 % of the variance in the soil bacterial diversity and 40 % in community composition. The results are valuable for understanding the dynamics of soil microbial community and potential carbon feedback to future climate warming in permafrost regions.