Hydrology defines microbial communities and functions across polygon types at the Next Generation Ecosystem Experiment (NGEE)-Arctic Barrow site
Permafrost soils are one of the world’s largest terrestrial carbon reservoirs thus an important focal point for climate change research. With increasing global temperatures, Arctic landscapes are changing and becoming a potential source of greenhouse gas (GHG) emissions. As part of the NGEE-Arctic, we investigated the microbial potential and mechanisms leading to GHG emissions at the Barrow Environmental Observatory (BEO). We collected seasonally thawed active layer soil samples along a transect containing high-, flat- and low-centered polygons for two consecutive years. The microbial community composition and genetic potential along the active layer were determined by sequencing of 16S rRNA genes and metagenomes.
The sequence data were positively correlated to in-situ GHG fluxes, lab-scale CH4-oxidation assays, and soil chemistry. Polygon type was the primary driver of microbial community composition; each polygon type had a distinct microbial community structure. However, the microbial communities shared many metabolic capabilities. For example, genes involved in degradation of complex organic compounds were found in all three types of polygons. On the other hand, not all the key metabolic pathways leading to GHG emissions were found across the BEO. For example, CH4 production potential was only found in low-centered polygons while CH4 oxidation and CO2 production potential were more prevalent in the high- and flat-centered polygons. These results were confirmed via lab-scale soil incubations. The metagenome sequence data suggested that nitrate was utilized as a nitrogen source, but not lost through denitrification. Metagenomics coupled with detailed measurements of geochemistry and microbial processes aids us in understanding the biogeochemical cycles in Arctic soils and in the future will better inform modeling efforts.