14 Apr 2026

Changes in Permafrost Bacterial Community Composition After Thaw Across Multiple Alaskan Locations

Abstract: 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.

9 Sep 2025

Active Layer and Permafrost Microbial Community Coalescence Increases Soil Activity and Diversity in Mixed Communities Compared to Permafrost Alone

Abstract: Permafrost is experiencing rapid degradation due to climate warming. Dispersal of microbial communities from the seasonally-thawed active layer soil into newly thawed permafrost may influence community assembly and increase carbon release from soils. We conducted a laboratory soil mixing study to understand how carbon utilization, heterotrophic respiration, and microbial community structure were affected when active layer and permafrost soils were mixed in varying proportions. Active layer soil and permafrost collected from two sites in Alaska were mixed in five different ratios and incubated for 100 days at 10°C. Respiration rates were highest in the 100% active layer soils, averaging 19.8 µg C-CO2 g−1 dry soil d−1 across both sites, and decreased linearly as the ratio of permafrost increased. Mixing of the two soil layers resulted in utilization of a more diverse group of carbon substrates compared to permafrost alone. Additionally, combining active layer and permafrost soils increased microbial diversity and resulted in communities resembling those from the active layer when soils were mixed in equal ratios. Understanding the effects of active layer-permafrost mixing on functional potential and soil organic matter decomposition will improve predictions of carbon-climate feedbacks as permafrost thaws in these regions.