Soil is a living organism made up of countless microscopic living beings. The number and variety of living microorganisms in the soil is immeasurable. In 1 g of soil there are billions of bacteria, fungi, algae and other organisms, and in addition, a great many earthworms, wood lice, centipedes, snails and other soil organisms, which, as a result of the metabolic process, process dead protein organisms and other organic residues into nutrients available for plant uptake. Thanks to their activity in the soil, humus is formed from the original plant and protein material, from which, as a result of combination with water and oxygen, nutrients for plants are released. Loose soil structure is also achieved largely due to the activity

soil organisms that naturally mix mineral and organic substances, producing a new enriched substance. This greatly increases the fertility of the soil. Soil animals are studied by a special branch of science - soil zoology, which was formed only in our century. After specialists developed methods for recording and fixing animals, which is associated with significant technical difficulties, the eyes of zoologists saw a whole kingdom of creatures, diverse in structure, lifestyle and their significance in the natural processes occurring in the soil. By biodiversity animal world soil can only be compared with coral reefs- a classic example of the richest and most diverse natural communities on our planet.

Among them are large invertebrates such as earthworms, and microorganisms that cannot be seen with the naked eye. In addition to small sizes (up to 1 mm), most soil-dwelling invertebrates also have an inconspicuous body color, whitish or gray, so they can be seen only after special treatment with fixatives, under a magnifying glass or microscope. Microorganisms form the basis of the animal population of the soil, the biomass of which reaches hundreds of centners per hectare. If we talk about the number of earthworms and other large invertebrates, then it is measured in tens and hundreds per square meter, and the number of small and microscopic organisms reaches millions and billions of individuals.

For example, protozoa and roundworms (nematodes) with a body size of up to 0.01 mm in their physiology are typically aquatic creatures that can breathe oxygen dissolved in water. The smallest sizes allow them to be content with microscopic droplets of moisture that fill the narrow soil cavities. There the worms move, find food, multiply. When the soil dries up, they are able to remain in an inactive state for a long time, being covered from the outside with a dense protective shell of hardening secretions.

Of the larger soil organisms, one can name soil mites, springtails, small worms - the closest relatives of earthworms. These are real land animals. They breathe atmospheric oxygen, inhabit air intrasoil cavities, root passages, and burrows of larger invertebrates. Small size, flexible

Soil organisms are a vital link in a closed metabolic cycle. Thanks to their vital activity, all products organic origin decompose, recycle and acquire a mineral form available to plants. Minerals, dissolved in water, come from the soil to the roots of plants, and the cycle begins again

body allow them to exploit even the narrowest gaps between soil particles and penetrate deep horizons of dense loamy soils. For example, shell mites go 1.5-2 m deep. For these small soil inhabitants, the soil is also not a dense mass, but a system of passages and cavities interconnected. Animals live on their walls, like in caves. Waterlogging of the soil is just as unfavorable for its inhabitants as drying out. Soil invertebrates with body sizes larger than 2 mm are clearly distinguishable. Here you can find various groups of worms, terrestrial mollusks, crustaceans (woodlice, amphipods), spiders, harvestmen, false scorpions, millipedes, ants, termites, larvae (beetles, dipterans and hymenoptera insects), butterfly caterpillars. Earthworms and some insect larvae have highly developed muscles. By contracting their muscles, they increase the diameter of their body and push the soil particles apart. The worms swallow the earth, pass it through their intestines and at the same time move forward, as if "eating" through the soil. Behind, they leave their excrement with metabolic products and mucus, abundantly excreted in the intestinal cavity. With these slimy lumps, the worms cover the surface of the passage, strengthening its walls, so such passages remain in the soil for a long time.

And insect larvae have special formations on the limbs, head, sometimes on the back, with which they act like a shovel. For example, in bears, the front legs are turned into strong digging tools - they are expanded, with jagged edges. These scrapers are able to loosen even very dry soil. In the larvae

beetles, digging passages to a considerable depth, use the upper jaws as loosening tools, which look like triangular pyramids with a jagged top and powerful ridges on the sides. The larva hits the soil lump with these jaws, breaks it into small particles and rakes them under itself. Other large inhabitants of the soil live in existing cavities. They are usually very flexible thin body and can penetrate very narrow and winding passages. digging activity animals has great importance for soil. The tunnel system improves its aeration, which favors the growth of roots and the development of aerobic microbial processes associated with humification and mineralization of organic material. No wonder Charles Darwin wrote that long before man invented the plow, earthworms learned how to cultivate the land properly and well. He dedicated a special book to them, "Formation of the Soil Layer by Earthworms and Observations on the Way of Life of the Last".

Main role soil organisms lies in the ability to quickly process plant residues, manure, household waste, turning them into high-quality natural organic fertilizer biohumus. In many countries, including ours, they learned to breed worms on special farms to obtain organic fertilizers. The following examples will help to evaluate the contribution of the invisible workers of the soil in the formation of its structure. Thus, ants building soil nests throw more than a ton of earth per 1 ha to the surface from deep layers of soil. For 8-10 years, they process almost the entire horizon inhabited by them. And desert wood lice raise from a depth of 50-80 cm to the surface the soil enriched with elements of mineral plant nutrition. Where there are colonies of these woodlice, the vegetation is taller and denser. Earthworms are capable of processing up to 110 tons of land per 1 ha per year.

Moving in the ground and feeding on dead plant residues, animals mix organic and mineral soil particles. Dragging the ground litter into the deep layers, they thereby improve the aeration of these layers, contribute to the activation of microbial processes, which leads to the enrichment of the soil with humus and nutrients. It is the animals that create the humus horizon and soil structure by their activities.

The role of earthworms in the biological life of the soil

Earthworms loosen the soil, penetrating, unlike other soil organisms that can live in only one soil layer, into different soil layers. Through the holes made by the worms, air and water penetrate the roots of the plants.

Earthworms contribute to the enrichment of the soil with oxygen, which prevents the processes of decay of organic material.

: Earthworms absorb organic residues, along with which mineral particles, clay grains, soil algae, bacteria, microorganisms enter the digestive tract. There, this heterogeneous material is mixed and processed, thanks to metabolic processes, supplemented by secretions of the intestinal microflora of the worm, acquiring a new state, and then enters the soil in the form of droppings. This qualitatively improves the composition of the soil and gives it a glued, lumpy structure.

Man has learned to cultivate the soil, fertilize it and get high yields. Does it replace the activity of soil organisms? To some extent, yes. But with intensive land use modern methods, when the soil is overloaded with chemicals (mineral fertilizers, pesticides, growth stimulants), with frequent violations of its surface layer and its compaction by agricultural machines, deep violations of natural processes occur, which lead to gradual degradation of the soil, a decrease in its fertility. Inflated quantities mineral fertilizers poison the earth and kill it biological life. Chemical treatments destroy not only pests in the soil, but also beneficial animals. It takes years to repair this damage. Today, in the period of ecologization of our thinking, it is worth thinking about what criteria to assess the damage caused to the crop. Until now, it was customary to count only losses from pests. But let's also calculate the losses inflicted on the soil itself from the death of soil formers.

To preserve the soil, this unique natural resource The land, capable of self-restoration of its fertility, must first of all preserve its wildlife. Soil organisms, soil formers do what a person with his powerful machinery cannot yet do. They need a stable environment. They need oxygen in the system of passages made and a supply of organic residues, shelters and passages that are not disturbed by humans. Smart farming, gentle tillage practices and maximum chemicals plant protection means the creation of conditions for the preservation of the living bioworld of the soil - the key to its fertility.

Soil nutrients

Plants can obtain all the components necessary for life from the soil only in mineral form. Nutrients rich in organic matter, humus and organic fertilizers can be assimilated by plants only after the completion of the decomposition process organic compounds or their mineralization.

The presence of a sufficient amount of nutrients in the soil is one of the main factors for the successful development of plants. Plants build their aboveground part, root system, flowers, fruits and seeds from organic substances: fats, proteins, carbohydrates, acids and other substances produced by the green leaf mass of plants. For the synthesis of organic substances, plants need ten main elements, which are called biogenic. Biogenic chemical elements are constantly included in the composition of organisms and perform certain biological functions that ensure the viability of organisms. Biogenic macronutrients include carbon (C), calcium (Ca), iron (Fe), hydrogen (H), potassium (K), magnesium (Mg), nitrogen (N), oxygen (O), phosphorus (P), sulfur (S). Some of these elements the plant receives from the air, for example, oxygen and carbon, hydrogen is obtained during the decomposition of water in the process of photosynthetic

The process of nutrient metabolism

Nutrients play an important role in the cyclic process of metabolism, ensuring the vital activity of plants. Water dissolves nutrients and trace elements, creating a soil solution that is assimilated by plant roots Solar energy promotes the conversion of nutrients through the process of photosynthesis, which, in turn, depends on the presence in plant tissues of a number of trace elements involved in the formation of the colored substance chlorophyll

For, the remaining elements come to the plant exclusively from the soil in the form of compounds dissolved in water, the so-called soil solution. If there is a serious deficiency of any of the elements in the soil, the plant weakens and develops only up to a certain stage, until it exhausts its internal biological supply of this element that exists in the tissues of the plant. After this stage, the plant may die. In addition to biogenic macroelements, microelements are necessary for the development of a plant, which are usually contained in very small quantities, but nevertheless play important role in exchange processes. Microelements include: aluminum (A1), boron (B), cobalt(Co), copper (Cu), manganese (Mn), molybdenum Mo), sodium (Na), silicon (Si), zinc (Zn). Hei - the balance or excess of trace elements leads to To metabolic disorders, which

behind a lag in the growth and development of the plant, reduced yields and other consequences. Some of the listed trace elements are not vital and are often identified by researchers in the group of so-called " useful elements". Nevertheless, their presence is required for full development plants. All components must be present in the nutrition of the plant in a balanced way, since the absence of at least one of the main elements, such as nitrogen, phosphorus, potassium or calcium, inevitably leads to the insufficiency or inability of the plant to assimilate the remaining three elements, as well as other nutrients. . That is why the presence of all the elements is so important for the full assimilation of the entire nutrient complex by the plant.

The ability of plants to absorb nutrients from the environment is determined by the quality and volume of the root system. Plants absorb nutrients throughout the growing season, but unevenly. The need of plants for nutrients changes in different periods of development. During the period of intensive growth, plants especially need nitrogen, during flowering and fruiting, the need for phosphorus and potassium increases. Assimilated nutrients are selectively fixed in various plant organs.

T.V. Lukarevskaya

When we enter the forest on a summer day, we immediately notice fluttering butterflies, singing birds, jumping frogs, we rejoice at a running hedgehog, a meeting with a hare. One gets the impression that it is these well-marked animals that form the basis of our fauna. In fact, the animals that are easy to see in the forest are only an insignificant part of it.

Soil animals form the basis of the population of our forests, meadows, and fields. The soil, at first glance so lifeless and unsightly, turns out to be literally crammed with life upon closer examination. If you look closely, unusual pictures will open.

Some of the inhabitants of the soil are easy to see. These are earthworms, centipedes, insect larvae, small mites, wingless insects. Others can be seen with a microscope. In the thinnest films of water that envelop soil particles, rotifers, flagellates scurry about, amoebas crawl, roundworms writhe. How many real workers are here, indistinguishable to the naked eye, but doing, nevertheless, a titanic work! All these inconspicuous beings keep our common Home- Earth. Moreover, they also warn of the danger that threatens this house when people behave unwisely in relation to nature.

In the soil of central Russia, per 1 m2, you can find up to 1 thousand species of soil inhabitants that differ greatly in number: up to 1 million ticks and springtails, hundreds of centipedes, insect larvae, earthworms, about 50 million roundworms, while the number of protozoa is even difficult to estimate .

This whole world, living according to its own laws, ensures the processing of dead plant residues, the cleaning of soils from them, and the maintenance of a water-resistant structure. Soil animals constantly plow the soil, moving up particles from the lower layers.

In all terrestrial ecosystems the vast majority of invertebrates (both in terms of the number of species and the number of individuals) are soil dwellers or are closely associated with the soil at a certain period of their life cycle. Boucle (1923) calculated that the number of insect species associated with the soil is 95–98%.

In terms of the ability to adapt to living conditions, there are no equal nematodes among animals. In this respect, they can only be compared with bacteria and the simplest unicellular organisms. Such universal adaptability is largely due to the development of a dense outer cuticle in nematodes, which increases their vitality. In addition, the shape of the body and the nature of the movements of nematodes turned out to be suitable for life in various environments.

Nematodes take part in the mechanical destruction of plant tissues: they “burrow” into dead tissues and, with the help of secreted enzymes, destroy cell walls, opening up pathways for bacteria and fungi to penetrate.

In our country, yield losses of vegetables, cereals and industrial crops due to damage by roundworms sometimes reach 70%.

Nematode

southern root-knot nematode Beet nematode

The formation of tumors - galls - on the roots of the host plant is caused by another pest - the southern root-knot nematode (Meloidogyne incognita). The greatest harm it brings vegetable growing in the southern regions, where it is found in open field. In the north, it occurs only in greenhouses, mainly damaging cucumbers and tomatoes. The main harm is caused by females, while males, having completed development, go into the soil and do not feed.

Soil nematodes are notorious: they are seen primarily as pests of cultivated plants. Nematodes destroy the roots of potatoes, onions, rice, cotton, sugar cane, sugar beet, ornamental and other plants. Zoologists are developing measures to combat them in the fields and in greenhouses. A great contribution to the study of this group of animals was made by the famous evolutionary biologist A.A. Paramonov.

Nematodes have long attracted the attention of evolutionists. They are not only extremely diverse, but also amazingly resistant to physical and chemical factors. Wherever they begin to study these worms, new ones are found everywhere, not known to science kinds. In this regard, nematodes seriously claim the second - after insects - place in the animal world: experts believe that there are at least 500 thousand species of them, but there is reason to believe that the true number of nematode species is much higher.

General characteristics.

Soil is a product of vital activity of organisms, including microorganisms, both modern and belonging to the "former biospheres". Soil is the most important component of any ecological land system, on the basis of which plant communities develop, which in turn form the basis of the food chains of all other organisms that form ecological systems Earth, its biosphere. People are no exception here: the well-being of any human society is determined by the availability and condition of land resources, soil fertility.

Meanwhile, during the historical time on our planet, up to 20 million km2 of agricultural land has been lost. Today, there is an average of only 0.35-0.37 hectares for each inhabitant of the Earth, while in the 70s this value was 0.45-0.50 hectares. If the current situation does not change, then in a century, at such a rate of losses, total area land suitable for agriculture will be reduced from 3.2 to 1 billion hectares.

V.V. Dokuchaev identified 5 main soil-forming factors:

the climate

parent rock (geological basis);

topography (relief);

· alive organisms;

Currently, another factor in soil formation can be called human activity.

Soil formation begins with primary succession, which manifests itself in physical and chemical weathering, leading to loosening from the surface of parent soils. rocks such as basalts, gneisses, granites, limestones, sandstones, shales. This weathering layer is gradually colonized by microorganisms and lichens, which transform the substrate and enrich it with organic matter. As a result of the activity of lichens, the most important elements of plant nutrition, such as phosphorus, calcium, potassium and others, accumulate in the primary soil. Plants can now settle on this primary soil and form plant communities that determine the face of biogeocenosis.

Gradually, deeper layers of the earth are involved in the process of soil formation. Therefore, most soils have a more or less pronounced layered profile, divided into soil horizons. A complex of soil organisms settles in the soil - edaphone : bacteria, fungi, insects, worms and burrowing animals. Edaphon and plants are involved in the formation of soil detritus, which is passed through their body by detritophages - worms and insect larvae.

For example, earthworms per hectare of land process about 50 tons of soil per year.

During the decomposition of plant detritus, humic substances are formed - weak organic humic and fulvic acids - the basis of soil humus. Its content provides soil structure and availability to plants. mineral elements nutrition. The thickness of the layer rich in humus determines the fertility of the soil.

The composition of the soil includes 4 important structural components:

mineral base (50-60% of the total composition of the soil);

· organic matter(to 10%);

air (15-20%);

water (25-35%).

Mineral base- an inorganic component formed from the parent rock as a result of its weathering. Mineral fragments vary in size (from boulders to grains of sand and the smallest particles of clay). It is the skeletal material of the soil. It is divided into colloidal particles (less than 1 micron), fine soil (less than 2 mm) and large fragments. The mechanical and chemical properties of the soil are determined by small particles.

The structure of the soil is determined by the relative content of sand and clay in it. The soil that contains sand and clay in equal amounts is most favorable for plant growth.

In the soil, as a rule, 3 main horizons are distinguished, differing in mechanical and chemical properties:

· Upper humus-accumulative horizon (A), in which organic matter is accumulated and transformed, and from which part of the compounds is carried down by washing water.

· Washout horizon or illuvial (B), where the substances washed from above are deposited and converted.

· parent rock or horizon (C), the material that is converted into soil.

Within each layer, more fractional horizons are distinguished, differing in their properties.

The main properties of the soil are ecological environment are her physical structure, mechanical and chemical composition, acidity, redox conditions, organic matter content, aeration, moisture capacity and moisture content. Various combinations of these properties form many varieties of soils. On Earth by prevalence leading position occupy five typological groups of soils:

  1. soils of humid tropics and subtropics, mainly red soils And zheltozems , characterized by the richness of the mineral composition and high mobility of organic matter;
  2. fertile soils of savannas and steppes - black soil, chestnut And brown soils with a powerful humus layer;
  3. poor and extremely unstable soils of deserts and semi-deserts belonging to different climatic zones;
  4. relatively poor soils of temperate forests - podzolic, sod-podzolic, brown And gray forest soils ;
  5. permafrost soils, usually thin, podzolic, marsh , gley , depleted in mineral salts with a poorly developed humus layer.

On the banks of the rivers there are floodplain soils;

Saline soils are a separate group: salt marshes, salt marshes, and etc. which account for 25% of soils.

Salt marshes - soils constantly strongly moistened with saline waters up to the surface, for example, around bitter-salty lakes. In summer, the surface of the salt marshes dries up, becoming covered with a crust of salt.

Salt licks - the surface is not saline, the upper layer is leached, structureless. The lower horizons are compacted, saturated with sodium ions; when dried, they crack into pillars and blocks. Water regime unstable - in spring - moisture stagnation, in summer - severe drying.

saline

Salty solonetzes

solonetsous soils (lightly salted)

Soil organic matter.

Each type of soil corresponds to a certain flora, fauna and a combination of bacteria - edaphon. Dying or dead organisms accumulate on the surface and within the soil, forming soil organic matter called humus . The process of humification begins with the destruction and grinding of the organic mass by vertebrates, and then it is transformed by fungi and bacteria. Such animals include phytophages that feed on the tissues of living plants, saprophages , consuming dead plant matter, necrophages feeding on the carcasses of animals, coprophages destroying animal excrement. All of them make up a complex system called saprofile complex of animals .

Humus differs in the type, form and nature of its constituent elements, which are divided into humic And non-humic substances. Non-humic substances are formed from compounds found in plant and animal tissues, such as proteins and carbohydrates. When these substances decompose, carbon dioxide, water, ammonia are released. The energy generated in this process is used by soil organisms. In this case, complete mineralization of the nutrients occurs. Humic substances as a result of the vital activity of microorganisms are processed into new, usually high-molecular compounds - humic acids or fulvic acids .

Humus is divided into nutritious, which is easily processed and serves as a source of nutrition for microorganisms, and stable, which performs physical and chemical functions, controlling the balance. nutrient, the amount of water and air in the soil. Humus tightly glues the mineral particles of the soil, improving its structure. Soil structure also depends on the amount of calcium compounds. The following soil structures are distinguished:

· mealy,

· powdery,

· grainy

· nutty

· lumpy

· clayey.

The dark color of humus contributes to better heating of the soil, and its high moisture capacity - to water retention by the soil.

The main property of the soil is its fertility, i.e. the ability to provide plants with water, mineral salts, air. The thickness of the humus layer determines the fertility of the soil.

Humidity and aeration.

Soil water is divided into:

· gravitational

· hygroscopic,

· capillary

· vaporous

Gravity water - mobile, is the main type of mobile water, fills wide gaps between soil particles, seeps down under the influence of gravity until it reaches groundwater. Plants easily absorb it.

Hygroscopic water in the soil is retained by hydrogen bonds around individual colloidal particles in the form of a thin, strong bonded film. It is released only at a temperature of 105 - 110 ° C and is practically inaccessible to plants. The amount of hygroscopic water depends on the content of colloidal particles in the soil. In clay soils it is up to 15%, in sandy soils - 5%.

As the amount of hygroscopic water accumulates, it passes into capillary water, which is retained in the soil by surface tension forces. Capillary water easily rises to the surface through pores from groundwater, easily evaporates, and is freely absorbed by plants.

Vaporous moisture occupies all water-free pores.

There is a constant exchange of soil, soil and surface water, changing its intensity and direction depending on the climate and seasons.

All pores free from moisture are filled with air. On light (sandy) soils, aeration is better than on heavy (clay) soils. The air regime and humidity regime are related to the amount of precipitation.

Ecological groups of soil organisms.

On average, the soil contains 2-3 kg/m2 of living plants and animals, or 20-30 t/ha. At the same time, in the temperate zone, plant roots are 15 t / ha, insects 1 t, earthworms - 500 kg, nematodes - 50 kg, crustaceans - 40 kg, snails, slugs - 20 kg, snakes, rodents - 20 gk, bacteria - 3 t, fungi - 3 t, actinomycetes - 1.5t, protozoa - 100kg, algae - 100kg.

The heterogeneity of the soil leads to the fact that for different organisms it acts as a different environment. According to the degree of connection with the soil as a habitat animals grouped into 3 groups:

· Geobionts - animals permanently living in the soil (earthworms, primary wingless insects).

· Geophylls - animals, part of the cycle of which necessarily takes place in the soil (most insects: locusts, a number of beetles, centipede mosquitoes).

· Geoxenes - animals that sometimes visit the soil for temporary shelter or shelter (cockroaches, many hemipterans, beetles, rodents, and other mammals).

Depending on the size of the soil inhabitants can be divided into the following groups.

· Microbiotype, microbiota soil microorganisms, the main link in the detritus chain, an intermediate link between plant residues and soil animals. These are green, blue-green algae, bacteria, fungi, protozoa. The soil for them is a system of micro-reservoirs. They live in soil pores. Able to tolerate freezing soil.

· macrobiotype, macrobiota large soil animals, up to 20 mm in size (insect larvae, centipedes, earthworms, etc.). the soil for them is a dense medium that provides strong mechanical resistance when moving. They move in the soil by expanding natural wells by moving apart soil particles or by digging new passages. In this regard, they developed adaptations for digging. Often available specialized bodies breathing. They also breathe through the integument of the body. For the winter and during the dry period, they move to deep soil layers.

· Megabiotype, megabiota - large shrews, mostly mammals. Many of them spend their whole lives in the soil (gold moles, mole voles, zokors, moles of Eurasia, marsupial moles of Australia, mole rats, etc.). They lay a system of holes, passages in the soil. They have underdeveloped eyes, a compact, valky body with a short neck, short thick fur, strong compact limbs, burrowing limbs, strong claws.

· The inhabitants of the holes - badgers, marmots, ground squirrels, jerboas, etc. They feed on the surface, breed, hibernate, rest, sleep, and escape from danger in soil burrows. The structure is typical for terrestrial ones, however, they have adaptations of burrows - strong claws, strong muscles on the forelimbs, a narrow head, small auricles.

· Psammophiles - sand dwellers. They have peculiar limbs, often in the form of “skis”, covered with long hairs, horny outgrowths (thin-clawed ground squirrel, crested jerboa).

· Gallophiles - inhabitants of saline soils. They have adaptations to protect against excess salts: dense covers, devices for removing salts from the body (larvae of desert beetles).

Plants are divided into groups depending on the requirements for soil fertility.

· Eutotrophic or eutrophic - grow in fertile soils.

· Mesotrophic - less demanding soils.

· Oligotrophic - satisfied with a small amount of nutrients.

Depending on the exactingness of plants to individual soil microelements, the following groups are distinguished.

· Nitrophils - demanding on the presence of nitrogen in the soil, they settle where there are additional sources of nitrogen - clearing plants (raspberries, hops, bindweed), garbage (nettle amaranth, umbrella plants), pasture plants.

· Calciophiles - demanding on the presence of calcium in the soil, settle on carbonate soils (lady's slipper, Siberian larch, beech, ash).

· calcium phobes - plants that avoid soils with a high content of calcium (sphagnum mosses, marsh, heather, warty birch, chestnut).

Depending on the pH requirements of the soil, all plants are divided into 3 groups.

· acidophiles - plants that prefer acidic soils (heather, white-bearded, sorrel, small sorrel).

· Basiphylls - plants that prefer alkaline soils (coltsfoot, field mustard).

· Neutrophils - plants that prefer neutral soils (meadow foxtail, meadow fescue).

Plants that grow in saline soils are called halophytes (European soleros, knobby sarsazan), and plants that cannot withstand excessive salinity - glycophytes . Halophytes have a high osmotic pressure, which allows the use of soil solutions, they are able to release excess salts through the leaves or accumulate them in their bodies.

Plants adapted to loose sands are called psammophytes . They are able to form adventitious roots when covered with sand, adventitious buds form on the roots when they are exposed, often have high speed shoot growth, flying seeds, strong covers, have air chambers, parachutes, propellers - devices for not falling asleep with sand. Sometimes a whole plant is able to break away from the ground, dry out and, together with the seeds, be carried by the wind to another place. Seedlings germinate quickly, arguing with the dune. There are adaptations for drought tolerance - root covers, root corking, strong development of lateral roots, leafless shoots, xeromorphic foliage.

Plants that grow in peat bogs are called oxylophytes . They are adapted to high soil acidity, strong moisture, anaerobic conditions (ledum, sundew, cranberries).

Plants that live on stones, rocks, scree are lithophytes. As a rule, these are the first settlers on rocky surfaces: autotrophic algae, scale lichens, leaf lichens, mosses, lithophytes from higher plants. They are called slit plants - chasmophytes . For example, saxifrage, juniper, pine.

How is the soil renewed? Where does she get the strength to “feed” such great amount various plants? Who helps create the organic matter on which its fertility depends? It turns out that under our feet, in the soil, a huge number of various animals live. If you collect all living organisms from 1 hectare of the steppe, then they will weigh 2.2 tons.

Representatives of many classes, orders, families live here in close proximity. Some process the remains of living organisms that enter the soil - they are crushed, crushed, oxidized, decomposed into constituent substances and create new connections. Others mix the incoming substances with the soil. Still others are laying collector passages that provide access to the soil for water and air.

Various non-chlorophyll organisms are the first to start working. It is they who decompose organic and inorganic residues that enter the soil, and make their substances available for plant nutrition, which, in turn, support the life of soil microorganisms. There are so many microorganisms in the soil that you will not find anywhere else. In just 1 g of forest litter, there were 12 million 127 thousand of them, and in 1 g of soil taken from a field or garden, there were only 2 billion bacteria, many millions of different microscopic fungi and hundreds of thousands of other microorganisms.

The soil layer and insects are no less rich. Entomologists believe that 90% of insects at one stage or another of their development are associated with the soil. Only in the forest floor Leningrad region) scientists have discovered 12 thousand species of insects and other invertebrates. In the most favorable soil conditions, up to 1.5 billion protozoa, 20 million nematodes, hundreds of thousands of rotifers, earthworms, mites, small insects - springtails, thousands of other insects, hundreds of earthworms and gastropods were found per 1 m2 of litter and soil.

Among all this variety of soil animals there are active helpers of man in the fight against invertebrate pests of forests, crops, garden and garden plants. First of all, these are ants. The inhabitants of one anthill can protect 0.2 hectares of forest from pests, destroying 18 thousand harmful insects in 1 day. Ants play a big role in the life of the soil itself. When building anthills, they, like earthworms, carry the earth out of the lower layers of the soil, constantly mixing humus with mineral particles. For 8-10 years in the area of ​​their activity, ants completely replace the topsoil. Their minks in the saline steppes help destroy salt licks. Like the passages of earthworms, they make it easier for plant roots to penetrate deep into the soil.

Not only invertebrates, but also many vertebrates live permanently or temporarily in the soil. Amphibians, reptiles arrange their shelters in it, breed their offspring. An amphibious worm spends its entire life in the ground.

The most common excavator is the mole, a mammal from the order of insectivores. He spends almost his entire life underground. The head, which immediately passes into the body, resembles a wedge, with which the mole expands and pushes the earth loosened by its paws on the sides in its moves. The paws of the mole turned into a kind of shoulder blades.

The short, soft coat allows it to move forward and backward with ease. Galleries-molehills, laid by a mole, stretch for hundreds of meters. For the winter, moles go deep into where the earth does not freeze, following their prey - earthworms, larvae and other invertebrate inhabitants of the soil.

Sand swallows, bee-eaters, kingfishers, rollers, puffins, or puffins, tube-nosed and some other birds arrange their nests in the ground, tearing out special holes for this. This improves the access of air to the soil. In places of mass nesting of birds, as a result of the accumulation of nutrients - fertilizers coming from the droppings, a kind of herbaceous vegetation is formed. In the north, their burrows have more vegetation than elsewhere. Burrows of rodents-diggers - marmots, mole voles, mole rats, ground squirrels, jerboas, voles - also contribute to a change in the composition of the soil.

Observations on soil animals, carried out in a school biological circle or a circle at the station of young naturalists on the instructions of scientists, will help expand your knowledge.

All around us: on the ground, in the grass, on the trees, in the air - life is in full swing everywhere. Even a resident who never went deep into the forest big city often sees around him birds, dragonflies, butterflies, flies, spiders and many other animals. Well known to all and the inhabitants of the reservoirs. Everyone, at least occasionally, had to see schools of fish near the shore, water beetles or snails.

But there is a world hidden from us, inaccessible to direct observation - a kind of world of soil animals.

There is eternal darkness, you cannot penetrate there without destroying the natural structure of the soil. And only a few, accidentally noticed signs show that under the surface of the soil, among the roots of plants, there is a rich and diverse world of animals. This is sometimes evidenced by mounds above mole burrows, holes in gopher burrows in the steppe or burrows of sand martins in a cliff above a river, heaps of earth on paths thrown out by earthworms, and they themselves, crawling out after rain, suddenly appearing masses of winged ants literally from under the ground. or fat larvae of May beetles, caught when digging up the earth.

Soil is usually called the surface layer earth's crust on land, formed during the weathering of the parent rock under the influence of water, wind, temperature fluctuations and the activities of plants, animals and humans. The most important property of the soil, which distinguishes it from the barren parent rock, is fertility, that is, the ability to produce crops (see Art. "").

As a habitat for animals, soil is very different from water and air. Try to wave your hand in the air - you will not notice almost any resistance. Do the same in water - you will feel a significant resistance of the environment. And if you put your hand in the hole and cover it with earth, it will be difficult to even pull it out, let alone move it from side to side. It is clear that animals can move relatively quickly in the soil only in natural voids, cracks, or previously dug passages. If none of this is available, then the animal can advance only by breaking through the passage and raking the earth back, or by “eating through” the passage, that is, by swallowing the earth and passing it through the intestines. The speed of movement in this case will, of course, be insignificant.

Burrowing animals and their passages in the soil: 1 - toad; 2 - cricket; 3- harvest mouse; 4 bears; 5 - shrew; 6 - mole.

Every animal needs to breathe in order to live. Conditions for respiration in soil are different than in water or air. Soil is composed of solid particles, water and air. Solid particles in the form of small lumps occupy a little more than half of its volume; the rest is accounted for by gaps - pores that can be filled with air (in dry soil) or water (in soil saturated with moisture). As a rule, water covers all soil particles with a thin film; the rest of the space between them is occupied by air saturated with water vapor.

Due to this structure of the soil, numerous animals can live in it, breathing through the skin. If they are taken out of the ground, they quickly die from drying out. Furthermore, hundreds of species of real freshwater animals live in the soil - the very ones that inhabit rivers, ponds and swamps. True, these are all microscopic creatures - lower worms and unicellular protozoa. They move, float in a film of water covering soil particles.

If the soil dries out, they release a protective shell and cease to be active for a long time.

Soil air receives oxygen from the atmosphere: its amount in the soil is 1-2% less than in atmospheric air. Oxygen is consumed in the soil by animals, microorganisms, and plant roots. They all emit carbon dioxide. In the soil air it is 10-15 times more than in the atmosphere. Free gas exchange between soil and atmospheric air can occur only if the holes between solid particles are not completely filled with water. After heavy rains or in the spring, after the snow melts, the soil is saturated with water. There is not enough air in the soil, and under the threat of death, many animals tend to leave the soil. This explains the appearance of earthworms on the surface after heavy rains.

Among soil animals there are predators and those that feed on parts of living plants, mainly roots. There are also consumers of decomposing plant and animal remains in the soil - perhaps bacteria also play an important role in their nutrition.

Soil animals find their food either in the soil itself or on its surface. The vital activity of many of them is very useful. Especially useful is the activity of earthworms, which drag a huge amount of plant debris into their holes: this contributes to the formation of humus and returns to the soil substances extracted from it by plant roots.

In forest soils, invertebrates, especially earthworms, recycle more than half of all leaf litter. For a year, on each hectare, they throw up to 25-30 tons of earth processed by them, turned into a good, structural soil, to the surface. If you distribute this land evenly over the entire surface of a hectare, you get a layer of 0.5-0.8 cm. Therefore, earthworms are not in vain considered the most important soil formers.

Not only earthworms “work” in the soil, but also their closest relatives - smaller whitish annelids (enchytreids, or potworms), as well as some types of microscopic roundworms (nematodes), small mites, various insects, especially their larvae, and finally woodlice, centipedes and even snails.

The purely mechanical work of many animals living in it also affects the soil. They make passages in the soil, mix and loosen it, dig holes. All this increases the number of voids in the soil and facilitates the penetration of air and water into its depths.

Such “work” involves not only relatively small invertebrates, but also many mammals - moles, shrews, marmots, ground squirrels, jerboas, field and forest mice, hamsters, voles, mole rats. The relatively large passages of some of these animals penetrate the soil to a depth of 1 to 4 m.

The passages of large earthworms go even deeper: in most worms they reach 1.5-2 m, and in one southern worm even up to 8 m. These passages, especially in denser soils, are constantly used by plant roots that penetrate deep into them.

In some places, for example in steppe zone, a large number of passages and holes are dug in the soil by dung beetles, bears, crickets, tarantula spiders, ants, and termites in the tropics.

Many soil animals feed on roots, tubers, and bulbs of plants. Those that attack cultivated plants or forest plantations are considered pests, such as the cockchafer. Its larva lives in the soil for about four years and pupates there. In the first year of life, it feeds mainly on the roots of herbaceous plants. But, growing up, the larva begins to feed on the roots of trees, especially young pines, and brings great harm to the forest or forest plantations.

Larvae of click beetles, dark beetles, weevils, pollen eaters, caterpillars of some butterflies, such as nibbling scoops, larvae of many flies, cicadas, and, finally, root aphids, such as phylloxera, also feed on the roots of various plants, severely damaging them.

A large number of insects that damage the aerial parts of plants - stems, leaves, flowers, fruits - lay eggs in the soil; here, the larvae hatched from the eggs hide during the drought, hibernate, and pupate.

Soil pests include some types of mites and centipedes, naked slugs and extremely numerous microscopic roundworms - nematodes. Nematodes penetrate from the soil into the roots of plants and disrupt their normal life.

Many predators live in the soil. "Peaceful" moles and shrews eat a huge amount of earthworms, snails and insect larvae, they even attack frogs, lizards and mice. They eat almost continuously. For example, a shrew eats an amount of living creatures equal to its own weight per day!

Predators are among almost all groups of invertebrates living in the soil. Large ciliates feed not only on bacteria, but also on simple animals, such as flagellates. The ciliates themselves serve as prey for some roundworms. Predatory mites attack other mites and tiny insects. Thin, long, pale-colored geophile centipedes, living in cracks in the soil, as well as larger dark-colored drupes and centipedes, keeping under stones, in stumps, in the forest floor, are also predators. They feed on insects and their larvae, worms and other small animals. The predators include spiders and haymakers close to them (“mow-mow-leg”). Many of them live on the surface of the soil, in bedding or under objects lying on the ground.

Many live in the soil predatory insects: ground beetles and their larvae, which play a significant role in the extermination of pests, many ants, especially larger species that exterminate a large number of harmful caterpillars, and finally, the famous antlions, so named because their larvae prey on ants. The ant lion larva has strong sharp jaws, its length is about 1 cm. The larva digs a funnel-shaped hole in dry sandy soil, usually at the edge of a pine forest, and burrows into the sand at its bottom, exposing only wide-open jaws. Small insects, most often ants, falling on the edge of the funnel, roll down. The ant lion larva grabs them and sucks them out.

In some places, a predatory ... mushroom is found in the soil! The mycelium of this fungus, which has a tricky name - didymozoophage, forms special trapping rings. Small soil worms - nematodes get into them. With the help of special enzymes, the fungus dissolves the rather strong shell of the worm, grows inside its body and eats it clean.

In the process of adapting to the conditions of life in the soil, its inhabitants developed a number of features in the form and structure of the body, in physiological processes, reproduction and development, in the ability to endure adverse conditions and in behavior. Although each type of animal has features that are only characteristic of it, in the organization of various soil animals there are also common features, characteristic of entire groups, since the living conditions in the soil are basically the same for all its inhabitants.

Earthworms, nematodes, most centipedes, the larvae of many beetles and flies have a highly elongated flexible body that allows them to easily move through winding narrow passages and cracks in the soil. Bristles in rain and others annelids, hairs and claws in arthropods allow them to significantly accelerate their movements in the soil and firmly hold in burrows, clinging to the walls of the passages. See how slowly the worm crawls over the surface of the earth and how quickly, in fact, instantly, it hides in its hole. Laying new passages, many soil animals alternately stretch and shorten the body. At the same time, abdominal fluid is periodically pumped into the anterior end of the animal. He. strongly swells and pushes soil particles. Other animals make their way by digging the ground with their front legs, which have become special bodies digging.

The color of animals constantly living in the soil is usually pale - grayish, yellowish, whitish. Their eyes, as a rule, are poorly developed or they are not at all, but the organs of smell and touch are very finely developed.

Scientists believe that life originated in the primitive ocean and only much later spread from here to land (see Art. ""). It is very possible that for some terrestrial animals the soil was a transitional medium from life in water to life on land, since the soil is a Habitat intermediate in its properties between water and air.

There was a time when only aquatic animals existed on our planet. After many millions of years, when land had already appeared, some of them hit the shore more often than others. Here, fleeing from drying out, they burrowed into the ground and gradually adapted to permanent life in the primary soil. Millions of years have passed. The descendants of some soil animals, having developed adaptations to protect themselves from drying out, finally got the opportunity to come to the surface of the earth. But they, probably, could not stay here for a long time at first. And they must have come out only at night. Until now, the soil provides shelter not only for “its own”, soil animals that live in it constantly, but also for many that come to it only for a while from water bodies or from the surface of the earth to lay eggs, pupate, go through a certain stage of development. , escape from heat or cold.

The soil animal world is very rich. It includes about three hundred species of protozoa, more than a thousand species of round and annelid worms, tens of thousands of arthropod species, hundreds of molluscs and a number of vertebrate species.

Among them there are both useful and harmful. But most soil animals are still listed under the heading "indifferent". Perhaps this is the result of our ignorance. Studying them is the next task of science.