Permafrost peatlands, containing a sizable amount of soil organic carbon (OC), play a pivotal role in soil (peat) OC transformation into soluble and volatile forms and greatly contribute to overall natural CO2 and CH4 emissions to the atmosphere under ongoing permafrost thaw and soil OC degradation. Peat microorganisms are largely responsible for the processing of this OC, yet coupled studies of chemical and bacterial parameters in permafrost peatlands are rather limited and geographically biased. Towards testing the possible impact of peat and peat pore water chemical composition on microbial population and diversity, here we present results of a preliminary study of the western Siberia permafrost peatland discontinuous permafrost zone. The quantitative evaluation of microorganisms and determination of microbial diversity along a 100 cm thick peat soil column, which included thawed and frozen peat and bottom mineral horizon, was performed by RT-PCR and 16S rRNA gene-based metagenomic analysis, respectively. Bacteria (mainly Proteobacteria, Acidobacteria, Actinobacteria) strongly dominated the microbial diversity (99% sequences), with a negligible proportion of archaea (0.3–0.5%). There was a systematic evolution of main taxa according to depth, with a maximum of 65% (Acidobacteria) encountered in the active layer, or permafrost boundary (50–60 cm). We also measured C, N, nutrients and ~50 major and trace elements in peat (19 samples) as well as its pore water and dispersed ice (10 samples), sampled over the same core, and we analyzed organic matter quality in six organic and one mineral horizon of this core. Using multiparametric statistics (PCA), we tested the links between the total microbial number and 16S rRNA diversity and chemical composition of both the solid and fluid phase harboring the microorganisms. Under climate warming and permafrost thaw, one can expect a downward movement of the layer of maximal genetic diversity following the active layer thickening. Given a one to two orders of magnitude higher microbial number in the upper (thawed) layers compared to bottom (frozen) layers, an additional 50 cm of peat thawing in western Siberia may sizably increase the total microbial population and biodiversity of active cells.

Climate warming, increased precipitation, and permafrost thaw in the Arctic are accompanied by an increase in the frequency of full or partial drainage of thermokarst lakes. After lake drainage, highly productive plant communities on nutrient-rich sediments may develop, thus increasing the influencing greening trends of Arctic tundra. However, the magnitude and extent of this process remain poorly understood. Here we characterized plant succession and productivity along a chronosequence of eight drained thermokarst lakes (khasyreys), located in the low-Arctic tundra of the Western Siberian Lowland (WSL), the largest permafrost peatland in the world. Based on a combination of satellite imagery, archive mapping, and radiocarbon dating, we distinguished early (<50 years), mid (50–200 years), and late (200–2000 years) ecosystem stages depending on the age of drainage. In 48 sites within the different aged khasyreys, we measured plant phytomass and productivity, satellite-derived NDVImax, species composition, soil chemistry including nutrients, and plant elementary composition. The annual aboveground net primary productivity of the early and mid khasyrey ranged from 1134 and 660 g·m−2·y−1, which is two to nine times higher than that of the surrounding tundra. Late stages exhibited three to five times lower plant productivity and these ecosystems were distinctly different from early and mid-stages in terms of peat thickness and pools of soil nitrogen and potassium. We conclude that the main driving factor of the vegetation succession in the khasyreys is the accumulation of peat and the permafrost aggradation. The soil nutrient depletion occurs simultaneously with a decrease in the thickness of the active layer and an increase in the thickness of the peat. The early and mid khasyreys may provide a substantial contribution to the observed greening of the WSL low-Arctic tundra.

&lt;p&gt;Climate warming and increased precipitation and permafrost thaw in the Arctic are accompanied by an increase in the frequency of a full or partial drainage of thermokarst (thaw) lakes. After lake drainage, abundant plant communities on nutrient-rich sediments may develop, but the specific features of this process remain extremely poorly known across the Arctic. Here, we examine case studies of lake basins located in the continuous permafrost zone of the largest peatland in the world, the Western Siberia Lowland (WSL). We characterize the vegetation and biological productivity of the drained thermokarst lake basins (khasyreys) located in the southern tundra of the WSL. The biological productivity of the khasyrey vegetation is a factor of two to nine higher than that in the surrounding tundra and the khasyreys may provide substantial contribution to observed greening of the northern part of the WSL (65 to 70&amp;#176;N). In the early successional stage, during the first years after the drainage, the seasonally thawed layer has maximal thickness. These wet mesotrophic ecotopes are rich in nutrients. The plant communities are represented by a dense herb layer of a hydrophilic species of sedges, grasses, and cotton grasses, covering 60&amp;#8211;70% of the area, whereas mosses cover &lt; 1%. In the mid successional stage, from 50 years after drainage, as plant litter is accumulated, and the nutrients are leached from the soil, the abundance of herbs decreases to 25&amp;#8211;40%, the abundance of mosses increases to 40&amp;#8211;60%, and the overall productivity of the plant communities decreases. The late stage of the succession khasyreys lasts several hundred years. The ecotopes are characterized by an accumulation of peat, which reaches a thickness of up to 40 cm on the soil surface. Among the vascular plants, which cover between 10% and 60% of the area, the abundance of herbaceous species is minimal, and dwarf shrubs prevail. The moss and lichen have continuous coverage. At this stage, the plant communities consist of mesotrophs and mesooligotrophs of a very low productivity, and the phytocoenoses are similar to the surrounding polygonal bogs. Overall, the main driving factor of the vegetation succession in the khasyreys is the accumulation of peat on the soil surface and microtopography of the lake bottom. The soil nutrient depletion occurs simultaneously with a decrease in the thickness of the active layer and an increase in the thickness of peat. The succession rate in different parts of the lake bottom varies, depending on the nutrient reserves in the initial sediment, the microlandscape, permafrost aggradation, and the content of redeposited peat.&lt;/p&gt;&lt;p&gt;This research was funded by the Russian Science Foundation (RSF) (project &amp;#8470; 18-77-10045).&lt;/p&gt;