Studies of the influence of different fertilizer options on the formation of the microbial biome were conducted, based on the generally accepted technology of growing agricultural crops: control – without fertilizers; fertilizer N45P42K55, by-products (3.0 t/ha) + N45P42K55, by-products (3.0 t/ha) + N60P50K65 and just by-products – 3.0 t/ha. The selection and analysis of soil samples was carried out in the phase of flowering and waxy maturity of spring barley from the upper (0–20 cm) arable root-containing layer of the soil. The number of microorganisms of the main physiological and taxonomic groups was determined by the method of sowing soil suspensions on the appropriate elective nutrient media. A comparative assessment of the ecological indices of microbiota formation in typical black soil showed a significant relationship between Shannon's indicators of biodiversity and Simpson's dominance in different phases of the ontogenesis of spring barley. It was determined that the use of ecological and industrial farming systems makes it possible to optimize microbiological processes during the period of active vegetation of spring barley, which contributes to the creation of conditions for increasing the number of ammonifying bacteria by 2.6–3.7 times, oligonitrophilic bacteria by 1.6–2.4 times, which use mineral forms of nitrogen, 2.5–6.5 times spore-forming and 1.5 times cellulose-destroying microorganisms. The diversity and trophically more complex structure of the phylotype structure of the soil bacterial microbocenosis after fertilization with by-products (3.0 t/ha) + N45P42K55 was revealed. It is based on two main clusters of dominant genotypes belonging to representatives of 33 species, 54 % of which are uncultivated. Under the option of by-products fertilization (3.0 t/ha) + N60P50K65, the qualitative composition of the soil microbocenosis was characterized by three clusters and a species richness of 17 species, of which 76 % were uncultivated. The qualitative composition
of the dominant genotypes of prokaryotes is 3.1 times richer when using organo-mineral fertilizer with an average rate of mineral fertilizers compared to the control option. Fertilization systems significantly affect the phylotype diversity of soil microorganisms. Fertilization with by-products (3.0 t/ha) + N45P42K55 leads to differentiation in the number of dominant genotypes in different soil layers.
Modern molecular biological methods open a wide perspective and new understanding of the phylogenetic and functional diversity of rhizosphere microbial communities. Further complex analysis makes it possible to evaluate the taxonomic and functional structure of the dominant strains of microorganisms using the selection of gene-specific primers and sequencing of full-length genomes. The main tool of phylogenetic research is the comparison of primary nucleotide sequences and sequential visualization of the results. The structure of the variable regions of the 16S rRNA gene is used as a phylogenetic marker. Bacterial DNA was isolated from the bacterial cell suspension using the GeneJet Genomic DNA Purification Kit (Thermo Scientific), according to the manufacturer's protocol. Amplification of the 16S rRNA gene was carried out with primers 27f (5′-AGAGTTTGATCMTGGCTCAG-3′) and 1492r (5′-CGGTTACCTTGTTTACGA CTT-3′) at the following temperature regime: 95 °С, 2 min; 30 cycles – 95 °С, 30 s; 55 °С, 45 s; 72 °С, 90 s; final elongation 72 °С, 7 min. A 25 μl PCR mix contained 12.5 μl 2× DreamTaq PCR Master Mix (Thermo Scientific), 30 pmol of each primer, and 50 ng of DNA. PCR was performed
on a Mastercycler Personal 5332 amplifier (Eppendorf, Germany).
As a result of the research, it was established that the bacteria Bacillus velezensis 10 and Phyllobacterium ifriqiyense 1 inhibited the growth of phytopathogenic micromycetes Fusarium sporotrichioides Sherb. 23.2 ‒ on 45.1 % and 77.4 %, respectively, test culture Alternaria alternata (Fr.) Keissl. 3.45 ‒ 63.1 % and 66.6 %, Nigrospora oryzae (Berk. & Broome) Petch. 18.77 ‒ 65.2 % and 86.7 %. Phyllobacterium ifriqiyense 1 bacteria colonize the substrate more quickly and use nutrients accordingly, at the same time, micromycetes lose the ability to grow and do not have the ability to further colonize the substrate,
a tendency to death is manifested. So, apparently, the revealed antagonistic activity is related to competition. Under natural conditions, this type of antagonism is most often observed in the soil environment of the rhizosphere of plants, where there is competition between microorganisms for food sources (root exudates). Therefore, the antagonistic activity of the studied bacterial strains dominating the rhizosphere of spring barley was manifested already on the third day of the experiment and strengthened its influence on the growth and development of phytopathogenic micromycetes throughout the experiment.
