A molecular approach on understanding seasonal effects on methane-related microbial processes in permafrost-affected soils from West Greenland

The warming Arctic is subjecting permafrost soils, which cover approximately 15 % of the northern land area, to drastically changing conditions. Thawing permafrost enables formerly inactive microbes to produce or oxidize methane (CH₄), a potent greenhouse gas. We present first data on seasonal observations of the microbial soil metagenome along two tundra soil moisture gradients on Disko Island, West Greenland.

Initial studies have been performed at a time of maximum active layer thickness in September 2022 and during snowmelt in June/July 2023. We show through metabarcoding (16S rRNA gene), that known methane oxidizers (methanotrophs) ubiquitously occurred at low relative levels throughout the whole soil community in September 2022, generally accounting for <1.5 % of all ASVs. During snowmelt in June/July 2023, methanotrophs appeared absent from all surface samples which were at dry to intermediately dry plots. They were mostly detectable below the active thawed layer (below ~10 cm). Methane producing archaea (methanogens) were predominantly present at the wet sites and at deeper depths – as it was expected based on anaerobic incubation experiments with the same samples. Similar to methanotrophs, they were much more prevalent at the thaw maximum in September than during snowmelt in June/July, adding up to almost ten times the amount of detected methanogens in June/July in their relative abundance.

Data from two additional field trips at times of the maximum active layer thickness (September 2023) and completely frozen and snow-covered soil (April 2024) will enable further insights into the seasonal variation of methane-related microbial communities. This data set will also be complemented by whole-genome metagenomics, adding information on seasonal changes in methane production and oxidation pathways. A final qPCR approach will add quantitative information to the metabarcoding-derived data. This way, we will be able to help understand the microbial functioning underlying CH₄-oxidation and production in different seasons, which in turn will be important for constraining the Arctic CH₄ budget, specifically during the shoulder seasons.