Biomass and Taxonomic Structure of Microbial Communities in Soils of the Right-Bank Basin of the Oka River

The data have been presented on the microbial biomass content and on the abundances and taxonomic structure of bacterial and archaeal communities in the upper horizons of gray forest (Eutric Retisol (Loamic, Cutanic, Humic)) and alluvial-meadow (Fluvic Gleyic Phaeozem (Loamic, Pachic)) soils of the autonomous, transitional, and accumulative positions of the slope landscape, corresponding to the fallow, small-leaved forest, and meadow ecosystems. Soil microbial biomass was measured by DNA quantification and chloroform fumigation-extraction; the archaeal and bacterial abundances were estimated using the FISH method; and the structure of microbial communities was analyzed via high-throughput 16S rRNA gene amplicon sequencing (DNA metabarcoding). The microbial biomass and the abundances of metabolically active bacterial and archaeal cells correlated with the organic carbon (Corg) and total nitrogen (Ntot) contents, increasing along the slope from the autonomous to accumulative landscapes, and decreasing with depth throughout soil profiles. The alluvial-meadow soil of the accumulative landscape was characterized by a sharp decrease in the relative abundance of Verrucomicrobia, as well as by the increase in the relative abundance of Proteobacteria and Firmicutes compared to the gray forest soil of the autonomous and transitional positions. The number of operational taxonomic units and α-diversity indices correlated significantly with C/N, Corg, and Ntot and were almost independent of the soil pH. Thus, location in landscape (catena) determined not only the physicochemical but also the microbiological properties of soil, forming the spatial heterogeneity of the microbial community structure and abundance.