Seasonal changes of microbial functions along high-Arctic tundra soil toposequences

High-arctic tundra-soil ecosystems are particularly sensible to global changes due to their proximity to freezing, snow cover, light availability and scarcity of vegetation. Seasonal dynamic are large in these biomes with a very short vegetation growing season. Hydrological fluctuations in these soils are also important, directly impacting the soil biological activity. Yet, little is known on the seasonal dyanmic in the regulation of microbial functions in high-arctic soils and their impact on greenhouses gas exchanges with the atmosphere. Fluxes of greenhouse gases (CO₂, CH₄ and N₂O) and microbial functions linked to C and N cylcing were assessed at each season along a slope toposequence in high-arctic tundra soils near Ny-Ålesund (Svalbard) and compared with prokaryotic and fungal community structures. Microbial functional diversity exhibited strong seasonal patterns, with most microbial functions acquiring C, N and P enhanced in summer, at the peak of the plant growing season. Seasonal dynamics was also evident for greenhouse gas fluxes but were not consistent across seasons. While CO₂ fluxes were clearly increased in summer, CH₄ fluxes were slightly higher in Autumn, especially in the upslope soils, alike methanogenesis gene abundance mcrA which distinctly increased in both biocrust and soil layer of the upslope site in Autumn. N₂O gas fluxes were clearly higher in both shoulder seasons (i.e. Spring and Autumn), when freeze-thaw cycle are frequents. Seasonal microbial functional changes however did not mirror the prokaryotic and fungal community structure, which were more influenced by the microtopography and the soil depth layers (biocrust vs underneath mineral soil). These findings highlight the intricate relationships between microbial functions, diversity, and environmental factors in high-Arctic soils and underscore the importance of considering both seasonal and microtopography factors in understanding soil microbial dynamics in Arctic ecosystems.