Evaluating Post-Fire Changes in Soil Microbial Communities Involved in Nitrogen Cycling in the Arctic Tundra

Arctic tundra wildfires are becoming more frequent due to global warming. Under this changing fire regime, important components of permafrost ecosystems, such as soils and their microbial communities, are disturbed by the burning of vegetation, organic soils, and their nutrients. Previous studies of tundra wildfires have documented significant changes in vegetation and nutrient pools following wildfire in the Arctic tundra, including an increase in inorganic nitrogen (N). Microbes are the main drivers of transformation of soil N, which is ultimately taken up by both microbes and plants. However, the microbial consequences of fire-induced shifts in inorganic N in Arctic soils have not been explored. This study aims to assess the postfire repercussions on soil microbial communities involved in N cycling. We sampled the microbial communities and soil physicochemical properties of peat plateau tundra sites in the Yukon Kuskokwim Delta, Alaska, which burned in 1972 and 2015, as well as unburned tundra sites as control. Characteristic vegetation patches (i.e., lichen, shrub, and moss) were targeted to investigate their relationship to N microbial communities. We also measured pH and oxidation-reduction potential (ORP) to account for the impact of post-fire soil chemistry on microbial communities. ORP measurements showed significant differences between vegetation patches and burned sites; these ORP differences might be an indicator of post-fire differences in the abundance of different groups of N-cycling bacteria (e.g., nitrifiers and denitrifiers). Through 16S amplicon sequencing, this study aims to characterize post-fire shifts in microbial communities involved in N cycling and link them to changes in N pools and fluxes to evaluate the potential long-term effects of wildfires on soils and plants in Arctic tundra.