Biotic component of soils
Distribution, soil biota composition
Scientific and technical support for the design, construction and reconstruction of structures for various purposes should include an analysis of the specifics of existing contamination of the biota of the underground space, the presence or possibility of micro- and macrobiological damage to soils, the influence of these processes on the change in the bearing capacity of sandy-clay rocks, stability and safety of functioning of the objects under study.
Biota (microbiota) - the whole aggregate of organisms (microorganisms) co-inhabiting the material (medium), regardless of the functional connections between them. To the biotic constituent of soils are various organisms for which soils serve as a temporary or permanent habitat. The area of existence of living organisms within the lithosphere is called the lithobiosphere, which is part of the biosphere. The upper limit of the lithosphere is the surface of the earth, and the lower boundary is determined by the depth of penetration of life into the rocks. Bacteria that oxidize hydrocarbons and form flammable gases (CH 4 , 1b, FbS), were traced in the section of Northern Ustyurt to a depth of 1100 m, and in the waters of the North Caucasus - below 2000 m. Microorganisms can exist in soils at a variety of conditions: one - at a temperature of minus 7 °, others - in boiling sources .
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The size of soil animals also varies widely. According to the size of the individuals of the representatives of the soil fauna, they were divided into groups (but Bashelya, 1963) :
• microfauna - less than 0.2 mm - protozoa, nematodes, rhizopods, echinococci that live in humid environments inside aggregates;
• mesofauna - from 0.2 to 4 mm - microarthropods, tiny insects, some myriapods and worms that live in intra-aggregate and interaggregate wet pores; macrophoon - from 4 to 80 mm - earthworms, mollusks, myriapods, insects (ants, termites, etc.)
• megafauna - animals larger than 80 mm - large insects, crabs, scorpions, moles, snakes, turtles, large and small rodents, foxes, badgers and other animals, burrowing in soil burrows <./p>
In soil science, biota is conventionally divided into macroorganisms and microorganisms.
To microorganisms * existing in the ground, include various (mainly higher) plants, fungi and multicellular animals. All animals found in soils are divided into three groups :
• geobionts - permanent inhabitants of soils (earthworms, centipedes, footworms);
• geofiles - living in the soil only for a part of the life cycle (larvae of crushes and crackers);
• Geoxenes - are temporarily sheltering in the soil (some insects).
• By type of nutrition, soil animals are divided into the following groups:
• phytophagous - feed on the tissues of the roots of living plants (the larvae of the May crunch are gnawed by pine roots, the beet root nematode is implanted in the roots of sugar beet, etc.);
• zoophagy - feed on other animals (all insectivorous animals, nematodes eating protozoa and rotifers, predatory mites feeding on nematodes, springtails, enchytraeids);
• necrophages - corpses of animals are used for food (ants-sliders in the deserts of Central Asia eat the remains of insects);
• saprophages - recycle dead plant remains, opal (worms, centipedes, woodworm, some cloves and insect larvae).
In most cases, the representatives of these groups are concentrated in the humus horizons of soils, and the more humus, the more diverse and abundant the fauna.
Animals play an important role in the redistribution of only plant residues, but also mineral salts. According to I.P. Babieva and G.M. Zenova (1983), the ground squirrel tolerates up to 1.5 t/ha of soil, and its hole penetrates to a depth of 2 m; Desert croaks settle in colonies up to 800 thousand individuals per hectare and during the summer they carry 0.5 t/ha of soil and 1 t of excrement, thereby increasing the porosity of the soil. 
Microorganisms are the most primitive and ancient living creatures on Earth. Microorganisms include pre-nuclear organisms (prokaryotes) and nuclear organisms (eukaryotes). The following groups of microorganisms are distinguished in the ground: fungi, algae, actinomycetes, mycobacteria, bacteria, rickettsia and viruses. Several groups of soil microorganisms are distinguished in field studies without the aid of a microscope. These include mold fungi, the white mycelium of which differs well in the forest litter or in the humus horizon; mycorrhizal fungi on the roots of some trees; nodule bacteria on the roots of legumes and on the roots of black alder, as well as algae, giving a solid black in a dry state and greening the cake on the surface and over the fissures of some soils in arid regions. Each type of soil, each genetic horizon has a specific composition of microflora and a specific density of microbial populations. On average, 1-10 g of soil contains 108-109 individuals of bacteria, 103-106 cells of lower fungi and actinomycetes. 103-104 cells of inferior algae, 102-103 cells of protozoa.
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All microorganisms are divided into heterotrophic and autotrophic. The development of autotrophic microorganisms occurs due to the light energy or oxidation energy of a number of inorganic compounds (hydrogen, sulfur, ammonia, iron, ). Heterotrophic microorganisms use for their life various organic substances, their individual representatives, very diverse in their properties, can develop both in the presence and in the absence of oxygen. Many heterotrophic microorganisms living in soils are able to develop in solutions very poor in nutrient elements (the concentration of organic substances in the solution can be no more than 5 mg/l); it is oligotrophic microorganisms, usually located on the surface of mineral parts and receiving food from the solutions washing them.It is well known that the importance of microorganisms in keeping the contents of various forms (solid, gaseous, organic and inorganic, easily and hardly soluble) of biophilic elements (N, C, H, P, O, S) at a certain level in soils at the expense of interrelated cyclic transformations. The processes of nitrogen fixation, nitrification, denitrification in the nitrogen cycle; synthesis and mineralization of complex polymer compounds of carbon; formation and absorption of hydrogen; dissolution and concentration of phosphorus compounds; binding and release of oxygen; oxidation of sulfides, thiosulphate, elemental sulfur and sulfate reduction in the sulfur cycle - all these processes are carried out by microorganisms or with their participation. There is enough data on the microbiological transformation of another 75 elements .
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