Microbial complexes of hydromorphic soils in the Selenga River delta (Baikal region)

The number and the biomass of microorganisms were determined in the soils of the floodplain and islands in the Selenga River delta. The population of fungi in the soils studied was low. The number of saprotrophic prokaryote microorganisms varied from 10⁶–10⁸ CFU/g of soil in the upper horizons to 10⁴–10⁵ CFU/g in the lower horizons of the soils. This pattern is typical for most zonal soils. The microbial biomass in the floodplain soils was 2–4 times as high as that in the soils of the islands. The number of microorganisms of different ecologic-trophic groups participating in the nitrogen and carbon mobilization was much lower than that in the hydromorphic soils of the Transbaikal region or in the cryogenic soils of the Angara River basin (Irkutsk district). The low coefficient of microbiological mineralization and the low coefficient showing the lack of nitrogen (coefficient of oligotrophness) in the soils indicated the weak processes of organic matter decomposition in the soils studied. During the season investigated (August–September), the bacterial complexes in all the soils were dominated by bacteria of the genera Bacillus, Pseudomonas, and Aquaspirillum. In the floodplain soils, streptomycetes constituted a considerable part of the microbial complexes of the floodplain soils, whereas, in the soils of the islands, their number was minor.