Composition and functioning of microbial communities in the decomposition of straw cereals in sod podzolic soil

Microbial transformation of fresh organic matter in arable soils defines different processes such as the global carbon cycle, food production and impacts on the environment. One of the available ways to improve the content of soil organic matter is the rational use of crop residues, such as straw. A limited use of straw is usually explained by its long decomposition in soil that leads to soil deficiency in mineral nitrogen and accumulation of phytotoxic compounds and phytopathogens. Therefore, the microbial preparations used to accelerate the cereals’ straw transformation may be of inrerest. In the model laboratory experiment we studied the effect of rye straw treatment with biopreparates BUGS (based on Bacillus ), Barcon (complex cellulosolitic association) and Omug (bio-fertilizer from litter poultry dung) developed in the ARRIAM, depending on the depth of seal (surficial, in a layer of 0-3 cm, in the layer 9-12 cm) of straw on the composition and functioning of soil microbial community. It is known that the most available organic compounds are decomposed in the first 2 weeks, so after 2 months we evaluated the effect of preparations and depth of placing straw into the soil on the bacterial community composition in the late stages of decomposition and destruction of difficulty decomposable compounds. During this period the straw decomposition is due generally to k-strategists. There is a perception that their community is more resistant to external influences and will not vary so much as r-strategists responsible for the early stage. After 60 days we determined the abundance of physiological groups of microorganisms, the microbial biomass, content of labile compounds of nitrogen and carbon, as well as respiration. We confirmed poor applicability of conventional microbiological analysis of physiological groups of microorganisms for the purposes of comparing the structure of microbial communities. There was a clear positive impact of straw on the abundance of amylolytic, pedotrofnyh and oligotrophic microorganisms. In this regard, the structure of the microbial community was evaluated by high-throughput sequencing libraries of 16S rRNA gene. A positive effect of straw on the number and activity of microorganisms, microbial biomass, labile organic carbon was shown. The tested preparations increased the straw decomposition, and the greatest effect, except Omug, was in a layer of 0-3 cm. Over 80 % of the soil bacterial community was represented by Proteobacteria and Actinobacteria, and the presence of Acidobacteria was lower due to the high fertility of the soil. Adding straw increased proportion of Actinobacteria and Betaproteobaktery compared to control. Actinobacteria were more involved in the decomposition of straw in the 9-12 cm layer, except the treatment with Barcon. It was shown that in case of Barcon and Omug, the biodiversity in the microbial community was higher (the Shannon index was 1.29-1.27 against 1.0-1.16 for control and untreated straw).