Microbial community of soil-like sub-strate as a potential source of non-symbiotic nitrogen-fixing strains

The aim of the study is to test the potential of a soillike substrate (SLS), which is a product of bioconversion of inedible phytomass in biological and technical life support systems, as a source of nitrogenfixing strains to improve nitrogen nutrition of plants. The objects of the study were nitrogenfixing strains Azotobacter chroococcum H1, A. chroococcum H2 and A. chroococcum H3, isolated by the authors from SLS. The object for comparison was the nitrogenfixing strain Azomonas macrocytogenes OSV2, isolated by the authors from agricultural soil, which had previously shown its effectiveness in field experiments as part of a complex biopreparation. The test objects were Lepidium sativum L. cress plants of the Moskovsky Greenhouse variety, grown in a climatic chamber in a sand culture under nitrogen deficiency conditions. Bacterization with all strains statistically significantly increased the growth indices of lettuce plants as a whole in terms of the totality of growth indices, the greatest increase was provided by strain H3, due to which the average values of the root system weight and length increased by 2.14 and 1.1 times, respectively, the weight and length of the aboveground part – by 1.5 and 1.31 times, and the weight and length of the whole plant – by 1.68 and 1.19 times relative to the nonbacterial control. Bacterization with all strains also statistically significantly increased the content of photosynthetic apparatus pigments (by 1.4–13.1 times relative to the control in terms of the fresh weight of leaves and by 1.2–11.9 times in terms of dry weight), and also increased the ratio of the sum of chlorophylls a and b to carotenoids by 1.1–1.6 times. However, in this case, strain OSV2 was the leader in efficiency. Bacterization with all the studied strains increased the nitrogen content in plants. The greatest effect in terms of stimulating plant growth and increasing the content of pigments of the photosynthetic apparatus was provided by bacterization with a mixture of strains H1, H2, H3 and OSV2, which allows us to talk about the presence of synergism in their effect on the plant.