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Significance of soil genesis for the composition and succession of bacterial communities during straw decomposition has been studied. Sterile grinded oat straw in nylon bags was placed in humus horizons of two soils (soddy-podzolic and chernozem; Albic Retisol (Abruptic, Ochric) and Haplic Chernozem (Pachic)) and incubated in the laboratory under constant hydrothermal conditions. On the basis of respiration dynamics (measured by absorption method) the stages of straw decomposition (early, middle and late) were specified. For each stage, the composition of bacterial communities was determined by high-performance sequencing of amplicon libraries of the variable region V4 of the 16S rRNA gene. It has been shown that carbon losses during decomposition of straw from the soddy-podzolic soil were higher than those from chernozem: 3913 ± 668 and 2981 ± 297 CO2 mg/m2 day, respectively. Phylogenetic analysis showed an increase in the diversity of the bacterial community in the process of straw decomposition: from 51 and 79 on the third day, up to 213 and 310 phylotypes from 17 phyla on the last day, for chernozem and soddy-podzolic soil, respectively. On the third day, Proteobacteria, Firmicutes, and Bacteroidetes were mainly present; on the 161st day, Actinobacteria were added. Soil had a significant impact on the taxonomic composition of straw communities. For the microbial community of straw formed on the basis of the microbiocenosis of soddy-podzolic soil the proportion of Proteobacteria was higher, but Bacteroidetes was lower, and the contribution of unidentified prokaryotes was more significant. Bacterial succession during straw decomposition had common features for both soils. The decomposition started with the quick consuming of easily available organic compounds of straw by copiotrophs, representatives of the Pseudomonas genus, the Stenotrophomonas genus from the family of Xanthomonaceae, and the Chitinophaga (Bacteroidia) genus. In addition to actinobacteria, the oligotrophs were represented by Firmicutes and part of Bacteroidetes. Throughout the entire observation period, probably due to the formation of available organic compounds during the decomposition of straw, the contribution of bacteria of the Rhizobiaceae family was significant. [ABSTRACT FROM AUTHOR]