Soil microorganisms

According to the research of S.N. Vinogradsky (1952) soil microflora can be divided into metabolically active organisms (R-strategists), which assimilate inorganic, low molecular weight organic substances and quickly ferment high-molecular organic compounds - proteins , cellulose , pectin , chitin ("zymogenic" microflora), and metabolically inactive organisms (k-strategists), capable of destruction and synthesis of humic substances ("autochthonous" microflora) ^[2] . S.P. Kostychev implied that plants serve as a source of nutrient substrates for microflora, which is the biologically active environment of the plant, supplying genetic resources for the evolution of symbiotic specialized forms ^[3] .

There are two main groups of atmospheric nitrogen-fixing microorganisms - those entering into symbiosis with higher plants (genera of bacteria Rhizobium , Bradyrhizobium , Mezorhizobium , Sinorhizobium , Azorhizobium ) ^[4] and free-living. The second group includes associative nitrogen fixers (genera of bacteria Azospirillum , Pseudomonas , Agrobacterium , Klebsiella , Bacillus , Enterobacter , Flavobacterium Arthrobacter , etc.) and microorganisms more adapted to free existence in the soil (genera of bacteria Clostridium , Azoterbacter , Be , .; phototrophic bacteria, cyanobacteria) ^[5] .

In the words of V. I. Vernadsky: "The soil is saturated with life." Viable microorganisms can produce several generations of their own per day. In 1 g of soil, the number of bacteria reaches one billion ^[6] .

A large number of microorganisms in the biosphere indicate studies D.I. Nikitin, according to their calculations, the microbial biomass in the soil exceeds the phytomass synthesized by higher plants annually ^[7] .

Research P.A. The tannery of the amount of microbial biomass of sod-podzolic and gray forest soils, as well as chernozem, showed that the share of pure microbial mass on average accounts for about 0.1% of the mass of soil. He considered the mechanisms of regulation of the number of microorganisms and approaches to managing the desired or undesirable microflora in the soil ^[8] .

Soil microflora decomposes organic substances and develops valuable forms of humus in the deep layers of the earth. Life processes in the soil play a key role in its structure, fertility, plant growth and development. In garden soil with a depth of arable layer up to 0.2 m, the number of microorganisms can be 7%, which means 42 kg of organic mass per 100 square meters ^[9] .

A study of soil microflora showed that the concept of microbiome, originally proposed by J. Lederberg et al. to characterize the total genome of the human intestinal microflora, can be partially extended to microbial communities of plants. The main functions of endophytic communities are to control pathogens and pests, as well as to release plants from xenobiotics coming from outside, and possibly from their own toxic metabolites. Some nodule bacteria are capable of fixing nitrogen. Such bacteria enter into symbiosis with legumes, penetrate their roots and cause the formation of " nodules " in which they multiply. These microorganisms are capable of fixing nitrogen, and the ammonia generated in this process is used by the plant for its own growth ^{[10] [11]} .

Some types of the microbial community of the soil can perform such functions as: assimilation of soil sources of nitrogen, phosphorus and iron, as well as the transformation and redistribution of metabolites between parts of the plant, which to some extent compensates for the lack of digestive organs. An important function of endophytes , especially under stress, can be the regulation of plant development by activating the synthesis of hormones, vitamins, and other biologically active substances ^[12] .

Two pathways of dissimilation nitrate reduction were found in various representatives of soil microflora. When developing in the natural habitat, denitrifying pseudomonads carry out both processes equally, in spore-bearing bacteria, the restoration of nitrate to ammonium nitrogen dominates. As a result of the denitrification processes in these microorganisms, significant losses of nitrogen from the medium were detected ^[13] .

Microscopic fungi are characterized by the most active and perfect energy metabolism in comparison with other soil microorganisms. The utilization of the substrate can reach 50-60%. In actinomycetes and bacteria, this indicator is slightly lower. The predominance of fungi in the microbial community, which decomposes plant debris, is explained not only by the high penetrating ability of fungal mycelium filaments (hyphae), but also by biochemical features. With the breakdown of cellulose, starch and soil pectins, a large amount of organic acids is formed, which increases the acidity of the soil, and this adversely affects its colonization by bacteria. Most microorganisms prefer a neutral reaction of the medium ^[14] .

Fungi biomass can actively develop both in the upper soil layers and with oxygen deficiency, for example, Fusarium (F. culmorum, F. oxysporum), Trichoderma viride, and some species of Aspergillus and Penicillium develop in deep soil layers. Compared to other soil organisms, fungi have an economical metabolism, since they use a large amount of carbon and nitrogen from the compounds they decompose to build their own body. Up to 60% of substances cleaved by fungi passes into the thallus of fungi, that is, they also fixate nitrogen ^[15] .

Soil microorganisms differ significantly from each other in morphology, cell size, relation to oxygen, needs for growth factors, and the ability to assimilate various substrates. There are over 100,000 types of microorganisms in the soil, but about 100 of them are used in industry ^[16] .

One of the most important tasks of agricultural microbiology is to elucidate the role of microorganisms in the agrolandscape, to isolate the most significant species, to study their functions, selection and introduction into the environment, which subsequently will allow the directional regulation of soil microbiological processes. Agricultural microbiology has become the most relevant area due to unforeseen consequences of the use of mineral fertilizers, pesticides and plant growth regulators. In most cases, this led to unpredictable climate changes and the loss of both the biological diversity of plants and animals, and a change in the microworld of the soil fertile layer. The need to use the biological capabilities of plants and microorganisms for partial or complete replacement of agrochemicals can successfully solve the problem of providing nutrients and protecting plants from diseases and pests ^[17] .

In determining the productivity of the plant-microorganism interaction, it is necessary to evaluate the compatibility of metabolic systems, for example, nitrogen and carbon transport routes, as well as the absence of active protective reactions in plants in response to the presence or penetration of microorganisms. Bacteria located in the rhizosphere or “nodules” can synthesize substances that stimulate ( phytohormones , vitamins ) as well as inhibit (rhizobiotoxins) plant development ^[18] .

Currently produced products in the following classes:

• Substances synthesized by certain soil microorganisms, for example phytohormones. ^[nineteen]
• Preparations of artificially propagated soil microorganisms of certain strains. For example, hay bacillus (Bacillus subtilis), or endophyte fungi.
• Preparations of artificially selected and artificially reproduced communities of microorganisms, for example, “effective microorganisms”.
• Preparations of natural communities of microorganisms of natural and artificial soils, for example, concentrated soil solution (CRC).

Thus, soil microflora differs in both species and functional diversity. The intensity of research in this area allows us to be optimistic about the future of agricultural microbiology. Depending on the goals, soil microflora can be successfully applied both in growing plants and processing various substrates, and in related fields, solving urgent problems of biotechnology.