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 (PBCs), thermokarst lake sediments (SBCs), and lake water (WBCs). Our study aimed to investigate the paired PBCs, SBCs, and WBCs 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 alpha diversity and higher beta diversity in WBCs than in SBCs and PBCs. However, up to 41 % of the OTUs were shared by PBCs, SBCs, and WBCs, suggesting that many taxa originate from the same sources via dispersal. SBCs and WBCs had reciprocal dispersal effects and both were correlated with PBCs. Dispersal limitation was the most dominant assembly process shaping PBCs and SBCs while homogeneous selection was the most dominant for WBCs. 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 beta 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.