Changes in permafrost bacterial community composition after thaw across multiple Alaskan locations

Increasing temperatures due to climate change are causing extensive permafrost thaw, impacting microbial communities and their processes. We conducted a laboratory thaw study comprising six Alaskan permafrost samples collected across a variety of locations to investigate how microbiome communities from different locations shift when experiencing the same thaw regime (stepwise increases in temperature over an 8-week incubation). The samples varied in bulk soil pH (4.45–6.59), water content (28%–265%), and carbon content (1%–29%). We surveyed the microbial community structure at each location pre- and post-thaw and determined whether communities were driven by stochastic or deterministic ecological assembly processes. We found that community composition and community assembly all varied by location. Dominant phyla were Firmicutes, followed by Actinobacteria and Proteobacteria. The deterministic process, homogeneous selection, was observed for five sites and was the most prevalent community assembly process at three of those sites, both pre- and post-thaw. At the two other sites, a combination of deterministic and stochastic processes influenced pre- and post-thaw community structure, with a large increase in drift post-thaw. Collectively, our findings suggest that permafrost attributes, such as edaphic conditions and pre-thaw community structure, exert an influence on the composition of microbial communities after thaw. However, the extent of this influence varies with location. The heterogeneous response of permafrost communities to thaw disturbance poses a significant challenge in accurately predicting the trajectory of microbial communities in response to climate change.