Microbial community composition explains wintertime greenhouse gas fluxes in an oroarctic tundra ecosystem

Microbial communities play a central role in regulating the greenhouse gas balance in soil ecosystems. Microorganisms are active in the cold, snow-covered Arctic tundra soils; however, their contribution to the greenhouse gas budget during the Arctic winter remains poorly understood. To investigate the functional activity of bacterial and archaeal communities in oroarctic tundra soils during late winter, metatranscriptomic samples were collected alongside greenhouse gas (GHG) flux measurements across key vegetation types, which represent pH and moisture gradients. The transcription of central carbohydrate metabolism genes, various stress-related genes, and high carbon dioxide (CO₂) fluxes evidenced active microbial metabolism in winter. Vegetation type, soil C/N ratio, pH, and water content explained the functional activity and microbial community composition during winter. The transcription of functional marker genes for methane oxidation and denitrification, coupled with flux data, suggests that shrublands and meadows act as methane (CH₄) sinks in winter, while all vegetation types function as small nitrous oxide (N₂O) sources. Our results further demonstrate that the soil microbial community has a significant impact on wintertime GHG emissions in the oroarctic tundra, thereby enhancing the explanatory power of a statistical model beyond that of abiotic environmental variables alone. This represents a promising step toward developing microbial-mediated models, which are crucial for improving predictions of ecosystem responses to climate change.