Examination of soil microbial communities after permafrost thaw subsequent to an active layer detachment in the High Arctic

Active layer detachments (ALDs) are permafrost disturbances associated with climate change and increased seasonal warming. Such perturbations result from thawing of the upper permafrost and downslope movement of the overlying thawed material, including the active layer. ALDs have the potential to impact soil microbial community composition and function in arctic soil ecosystems. Here we report an initial investigation of an ALD located at Cape Bounty on Melville Island in the Canadian High Arctic. We examined soil nutrient content as well as microbial community structure using denaturing gradient gel electrophoresis and sequencing. Soil from the disturbed site showed changes in microbial communities with strikingly different fungal community composition compared to soils from an adjacent undisturbed site. These community changes were correlated with enhanced levels of dissolved organic carbon, microbial carbon, total dissolved nitrogen, and microbial nitrogen. The Nitrososphaerales-an order of ammonia-oxidizing Archaea-were more abundant in the disturbed soil and may have been responsible for the altered nitrogen cycling that resulted in higher levels of total dissolved nitrogen there. The fungal communities at both sites were dominated by orders within the Ascomycota, a phylum of mainly hyphal fungi. Intriguingly however, they were more numerous in the undisturbed soil compared to the disturbed soil, suggesting that certain Ascomycota could not reestablish within six years of the ALD, and more generally that fungal hyphal networks may help to stabilize tundra surface soils against erosional losses.