Soil microbiocoenosis in the agricultural environment as a dynamic system: primary results of the assessment of changes

Soil biota is characterized by high structural, taxonomic and functional diversity and determines the leading trends in the process of soil formation, while the microorganisms content in the soil varies widely depending on its chemical composition, humidity, temperature, pH and other properties. On the other hand, the soil microbiome has a significant impact on soil fertility, participating in the conversion of nutrients inaccessible to plants into usable forms. Soil microbiota can promote or inhibit plant growth. The purpose of this work is to conduct a comparative analysis of the leading representatives of the microbiome for soil samples from the territory of the model field of the peasant (farm) economy Tsirulev E.P. (Privolzhsky District of the Samara Region). Soil sampling was carried out in accordance with the methods of sampling and sample preparation for chemical, bacteriological, helminthological analysis. For comparison, 15 samples were taken from the same points of the field in different years – 2019 and 2020. Soil suspensions were prepared according to the serial dilution method. Sowing dilutions was carried out on potato-glucose agar. Microorganisms were identified by microscopic method. The test result was calculated separately for fungi and bacteria. The ratio of fungi and bacteria in % to their total number was determined by calculating the number (N) of microorganisms present in the sample. Chemical analysis of soil samples was carried out according to the following parameters: water pH, salt pH, mass fraction of organic matter, mobile potassium and mobile phosphorus, exchangeable calcium and exchangeable magnesium. Laboratory study of soil samples taken on a model field from the territory of a peasant (farm) economy Tsirulev E.P. showed a fairly stable level of water and salt pH values, moderate variability in the content of organic matter, mobile potassium, magnesium and calcium, with a high heterogeneity of the spatial distribution of mobile phosphorus in the soil. Identification of the presence and abundance in soil samples of typical representatives of soil microbiocoenosis (12 broad-spectrum phytopathogens and 2 phytopathogen antagonists) made it possible to detect microorganisms: – common in this soil environment in both years of research (causative agents of phomosis, yellow mucous bacteriosis); – found for samples of one year in the minimum number of samples, not detected in another year (causative agent of verticillium, gray mold) or significantly increased their presence (causative agents of rhizoctoniosis, anthracnose, cladosporiosis). The presence in a significant proportion of soil samples, from 20 to 50–80% of the samples, was noted for a significant group of objects (Alternaria, Fusarium, Aspergillus, Penicillium, Rhisopus), in both years of research, the presence of the phytopathogen antagonist Trichoderma was detected in all samples. The question of the connection between the revealed changes in the composition of the soil microbiome and the species of plants that were cultivated in this field during a given growing season requires additional data to be clarified, which we will do in subsequent years. Nevertheless, the primary data obtained confirm the existing ideas about the lability of soil microbiocoenosis as a dynamic system that changes its state in response to the impact of abiotic (temperature, humidity) and biotic factors.