The monitoring network for the measurement of atmospheric and soil climate parameters was created at the southern boundary of the permafrost zone within the territory of the Republic of Buryatia, Russian Federation. Based on the obtained data, the processes of soil freezing and thawing were studied. Negative temperatures in cold soils occurred within 5.5–6 months, whereas the subsoil was in a thawed state most of the year. On the contrary, permafrost-affected soils were thawed for 4.5–5 months, remaining frozen in the subsoil for most of the year. We propose referring to the observed spatial–temporal differences in the temperature dynamics as the “mirror imaging” of the distribution of heat and cold (frost) in the studied soils of the permafrost zone.

The basis for assessing the stability of geosystems to changes in external heat cycle conditions is the calculation method. It is shown that permafrost soils are characterized by increased values of annual heat cycle Q_Y ≥ 300 MJ/m², i.e., half-sum of heat arrival and flow rate per year. This is due to the high heat consumption for melting soils (Q_Ph = 0.7–0.8 Q_Y) and warming them in the negative temperature range (Q_F). The heat cycle in frozen soil (Q_F) always has more heat cycle than in the thawed soil (Q_H). The condition Q_F > Q_H means the dominance of processes occurring at negative temperature, and the difference Q_{F −} Q_H is a quantitative assessment of the energy stability of soils to changes in heat exchange conditions on the surface.

Soil microbial communities play key roles in biogeochemical cycles and greenhouse gas formation during the decomposition of the released organic matter in the thawing permafrost. The aim of our research was to assess the taxonomic prokaryotic diversity in soil-ecological niches of the Darkhituy-Khaimisan transect during the initial period of soil thawing. We investigated changes in the microbial communities present in the active layer of four sites representing distinct habitats (larch forest, birch forest, meadow steppe and thermokarst lake). We explore the relationship between the biogeochemical differences among habitats and the active layer microbial community via a spatial (across habitats, and with depth through the active layer) community survey using high-throughput Illumina sequencing. Microbial communities showed significant differences between active and frozen layers and across ecosystem types, including a high relative abundance of Alphaproteobacteria, Firmicutes, Crenarchaeota, Bacteroidota and Gemmatimonadota in the active layer and a high relative abundance of Actinobacteriota and Desulfobacterota in the frozen layer. Soil pH, temperature and moisture were the most significant parameters underlying the variations in the microbial community composition. CCA suggested that the differing environmental conditions between the four soil habitats had strong influences on microbial distribution and diversity and further explained the variability of soil microbial community structures.

In this article the true affiliation is A. V. Bazarov a* , N. B. Badmaev b, c , S. A. Kurakov d, e, and B.-M. N. Gonchikov b aInstitute of Physical Materials Science, Siberian Branch, Russian...