Contrasting methanotrophic communities between upland and polygonal tundra and their link to nitrogen metabolism and methane uptake in the Western Canadian Arctic

Atmospheric methane (CH 4 ) uptake by arctic soils is widespread in dry tundra ecosystems. However, the environmental controls regulating CH 4 uptake are poorly understood, particularly such as soil nutrient availability or microbial community composition. Here, we analyzed the relative abundance and community structure of functional gene markers associated with CH 4 and mineral nitrogen (N) cycling in two contrasting tundra types in the Western Canadian Arctic using a targeted metagenomics approach. Microbial data were compared to soil properties, macro- and micronutrient concentrations, and CH 4 fluxes during an entire growing season (May–August). We find that soil pH was the most important control on gene distribution between the studied microsites. Methanotrophs associated with the upland soil cluster α (USCα) dominated in polygonal tundra (low pH), while USCγ dominated in upland tundra (high pH). Methane uptake rates ranged from -15 to -27 μg CH 4 –C m -2 h -1 (growing season mean) and increased with higher relative abundances of USCα and USCγ. Although CH 4 uptake rates were similar between microsites, our microbial data indicate different mechanisms to cope with N limitation in these nutrient-limited tundra environments: upland tundra was characterized by genes involved in denitrification and N retention, while polygonal tundra contained genes associated with biological N fixation. Our study highlights the need for an integrated view on interactions between CH 4 oxidation and N availability for methanotrophs in arctic tundra soils. • Atmospheric methane uptake commonly occurred at the studied tundra microsites • Despite similar uptake rates methanotroph communities differed between microsites • Soil pH was the most important control on gene distribution • Different mechanisms to cope with N limitation between upland and polygonal tundra