Differentiation of cognate bacterial communities in thermokarst landscapes: implications for ecological consequences of permafrost degradation

Abstract. Thermokarst processes likely result in new habitats harboring novel bacterial communities in degraded permafrost soil (PB), thermokarst lake sediments (SB), and lake water (WB). Our study aimed to investigate the paired PB, SB, and WB across the Qinghai–Tibet Plateau (QTP) by assessing the spatial pattern of diversity as well as assembly mechanisms of these bacterial communities. Each habitat had distinct bacterial assemblages, with lower α diversity and higher β diversity in WB than in SB and PB. However, up to 41 % of the operational taxonomic units (OTUs) were shared by PB, SB, and WB, suggesting that many taxa originate from the same sources via dispersal. SB and WB had reciprocal dispersal effects, and both were correlated with PB. Dispersal limitation was the most dominant assembly process shaping PB and SB, while homogeneous selection was the most dominant for WB. Bacterial communities of the three habitats correlated differently with environmental variables, but latitude, mean annual precipitation, and pH were the common factors associated with their β diversity, while total phosphorus was the common factor associated with their assembly processes. Our results imply that thermokarst processes result in diverse habitats that have distinct bacterial communities that differ in diversity, assembly mechanisms, and environmental drivers.