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Soil properties and functions are largely determined by the amount of available organic matter, which is most significant for the vital activity of microorganisms. The influence of the content of available soil organic matter on the composition and functioning of microbial community during the transformation of barley straw in the soil was studied. Samples from the upper 20-cm-thick layer of soddy-podzolic soil (Umbric Albic Retisols (Abruptic)) were incubated (T = 25°C, 60% TFC) for 4 months, and a model soil with a reduced content of available organic matter was obtained. Then, we performed a laboratory experiment with the application of barley straw into native and model soils. The dynamics (0, 7, 40, and 70 days) of soil respiration, microbial biomass (SIR), the number of microorganisms, and the taxonomic composition of the microbial community (16S-rRNA sequencing) were analyzed. The quality of soil organic matter was assessed from data on the contents of total organic carbon (Ctot) and its available (Cavail), water-soluble (Cwat), and labile (Clab) fractions. It was shown that the amount of Cwat and Cavail in the model soil decreased by half in the absence of significant differences in Ctot. The aggregate structure of the soil worsened, and the straw transformation proceeded 25% faster as compared with that in the native soil. The taxonomic composition of the soil bacterial community was influenced by the amount of available organic matter in the soil, the addition of straw, and the incubation period. A decrease in the content of available organic matter caused changes in the composition of the microbial community: the portions of the phyla Acidobacteria and Firmicutes decreased, while those of Actinobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, and archaea increased. It was found that the main part (50% of the total) of the microbial community of the depleted soil is characterized by great diversity and oligotrophy. Indicators for comparing soils by the degree of oligotrophy of the microbial community are proposed on the basis of data on its taxonomic composition. [ABSTRACT FROM AUTHOR]

The composition of rhizosphere microbial communities was studied for different species and varieties of agricultural gramineous plants (rye and wheat) grown in the soils contrasting in a number of agrochemical parameters. The data on analysis of the rhizosphere microbial communities obtained by sequencing of the V4 variable region of the 16S rRNA gene and on the ion and mass spectral composition of soil extracts are presented. Alpha diversity indices of the rhizosphere and control communities were almost the same. Analysis of beta diversity revealed higher variability of the rhizosphere microbial communities for chernozem-grown plants. Rhizosphere communities of the plants grown on sod-podzol soil were more similar and formed separate clusters. The taxa reliably involved in formation of specific rye and wheat rhizosphere microbiomes were established. Both common rhizosphere taxa (Sphingobacteriia, Betaproteobacteria) and species- or variety-specific ones (Oxalobacteraceae, Sphingobacteriaceae) were determined. Ion concentrations in soil extracts varied significantly depending on the soil type, while the similarity of mass spectral profiles depended more on the plant species than on the soil type. [ABSTRACT FROM AUTHOR]