The Structure of Microbial Communities in Soils of Noncryogenic Regressive Bog

Regressive development is widespread in peatlands of the northern hemisphere; a new type of peatlands—regressive bogs—should be introduced in addition to the traditional peatland types, such as eutrophic, mesotrophic, and oligotrophic peatlands. Diagnostic features and classification of soils typical of regressive bogs have already been discussed in relevant scientific literature. However, there are virtually no data on the microbiological analysis of soils of the aforementioned bog types. The aim of this study is to identify structural and functional organization of the microbial communities in soils of a regressive noncryogenic bog (sampling area in Tver oblast of the West Dvina Forest-Bog Station of the Institute of Forest Science, Russian Academy of Sciences). Numerous black bare peat spots without sphagnum mats, from 0.05 to 1 m2 in area demonstrate a high degree of regressive process at the studied bog. Data on the number and biomass of microorganisms were obtained by direct method of fluorescence microscopy. The taxonomic composition of bacterial and fungal communities was determined by plate method, while direct microscopy was used for algal communities. The CO2 and CH4 emissions were analyzed using chamber method. It was found that the total microbial biomass in the soils under regressive spots is higher than in the soils without any features of regressive process; the regressive peat mat had its own biomass reaching 50% of the total biomass in the active layer. Algae predominate in the biomass of regressive peat mats. Bacteria and fungi constitute 13–26% of the total biomass of regressive peat mats. Regressive mats are characterized by a high number of algae and bacteria. It should be noted that all algae genera found in the regressive peat mats represent the species characteristic of oligotrophic peatlands. Fungi of regressive peat mats were represented by mycelium and spores. During the wet period, the length of fungal mycelium rapidly increased by one–two orders of magnitude and reached 2–4 km/g. The domination of Penicillium miczynskii and Umbelopsis vinacea species, which typically predominate in eutrophic peatlands, can be considered a specific feature of the micromycetal complex of the regressive peat mat. Regressive peat mats are characterized by higher rates of plant residues mineralization because of the accumulation of nitrogen. This leads to an increase in the carbon dioxide emission, on the one hand, and to an inhibition of methanogenesis, on the other hand.