Permafrost soils differ significantly from other soils since they serve as a huge reservoir organic carbon accumulated during the Quaternary Period, which is in potential risk to be released in conditions of observed Arctic warming. This paper is aimed to characterize existing carbon pools, possible mineralization risks of soil organic matter and assess microbial communities in tundra and forest tundra permafrost soils of southern Yamal region. Profile distribution of carbon, nitrogen and C:N ratio showed non-gradual changing with the depth due to manifestation of cryopedogenesis in soil profiles which lead to cryogenic mass transfer. Mean carbon stocks for study area were 7.85±2.24 kg m-2 (for 0-10 cm layer), 14.97±5.53 kg m-2 (for 0-30 cm), 23.99±8.00 kg m-2 (for 0-100 cm). Analysis of humus type revealed the predominance of highly mineralizable low-molecular fragments which testifies high mineralizing risks in system of humus substances in conditions of Arctic warming. The taxonomic analysis of the soil microbiomes revealed 48 bacterial and archaeal phyla, among which Proteobacteria (27% on average), Actinobacteria (20%), Acidobacteria (13%), Chroloflexi (12%), Gemmatimonadetes (7%), Verrucomicrobia (7%), Planctomycetes (6%), Bacteroidetes (2 %), AD3 (3%) and Nitrospirae (3 %) constituted the majority (more than 95% of sequences in the amplicon libraries). The number of OTUs was higher in topsoils with more decomposed Histic horizons. This is probably due to less acidic pH (acidoneutral) in topsoil horizons values compared to other studied sites (exclusively acidic). This is in line with the results of basal respiration analysis showed the higher values in corresponding samples. To estimate alpha diversity, the indices for richness (observed species, ChaoI) and evenness (Faith’s index, Shannon evenness) were calculated. pH range and nitrogen accumulation were found as the main environmental factors describing the microbial community diversity and composition in studied soils. pH was found in strong positive correlation with Shannon index and in moderate positive correlation with phylogenetic diversity index. Whereas soil microbial communities have been studied quite detailed in temperate environments, little information is published for the permafrost environments. It is of particular interest the issues of comprehensive study of microbial diversity and its effects on the functioning and stability of the Arctic and sub-Arctic ecosystems, the carbon dynamics controlled by microbiome, and significance of changing environmental conditions for microbiome functioning in the Arctic, which remain poorly understood. This work is supported by Russian Scientific Foundation, project № 17-16-01030.
