Soil habitat. Soil as a habitat

Soil as an environmental factor

Introduction

Soil as an ecological factor in plant life. Properties of soils and their role in the life of animals, humans and microorganisms. Soils and land animals. Distribution of living organisms.

LECTURE No. 2,3

SOIL ECOLOGY

TOPIC:

Soil is the basis of the nature of land. One can endlessly be amazed at the very fact that our planet Earth is the only one known planets, which has an amazing fertile film - soil. How did soil originate? This question was first answered by the great Russian encyclopedist M.V. Lomonosov in 1763 in his famous treatise “On the Layers of the Earth.” Soil, he wrote, is not primordial matter, but it originated “from the decay of animal and plant bodies over the long course of time.” V.V. Dokuchaev (1846--1903), in his classic works on soils in Russia, was the first to consider soil as a dynamic rather than an inert medium. He proved that soil is not dead organism, and living, inhabited by numerous organisms, it is complex in its composition. He identified five main soil-forming factors, which include climate, parent rock (geological basis), topography (relief), living organisms and time.

The soil is special nature education, which has a number of properties inherent in living and inanimate nature; consists of genetically related horizons (form a soil profile) resulting from transformations of the surface layers of the lithosphere under the combined influence of water, air and organisms; characterized by fertility.

Very complex chemical, physical, physicochemical and biological processes flow in the surface layer rocks on the way to their transformation into soil. N.A. Kachinsky in his book “Soil, Its Properties and Life” (1975) gives the following definition of soil: “Soil must be understood as all surface layers of rocks, processed and changed by the joint influence of climate (light, heat, air, water) , plant and animal organisms, and in cultivated areas and human activity, capable of producing crops. The mineral rock on which the soil was formed and which, as it were, gave birth to the soil, is called parent rock.”

According to G. Dobrovolsky (1979), “soil should be called the surface layer globe, possessing fertility, characterized by an organo-mineral composition and a special, unique profile type of structure. Soil arose and develops as a result of the combined influence of water, air, solar energy, plant and animal organisms on rocks. Soil properties reflect local characteristics natural conditions" Thus, the properties of the soil in their totality create a certain ecological regime, the main indicators of which are hydrothermal factors and aeration.

Soil composition includes four important structural components: mineral base (usually 50 -- 60% general composition soil), organic matter (up to 10%), air (15 - 25%) and water (25 - 35%).

Mineral base (mineral skeleton) of soil is the inorganic component formed from the parent rock as a result of its weathering. The mineral fragments that form the soil skeleton are varied - from boulders and stones to sand grains and tiny particles clay. Skeletal material is usually randomly divided into fine soil (particles less than 2 mm) and larger fragments. Particles less than 1 micron in diameter are called colloidal. The mechanical and chemical properties of soil are mainly determined by those substances that belong to fine soil.

Soil structure determined by the relative content of sand and clay in it.

An ideal soil should contain approximately equal amounts of clay and sand, with particles in between. In this case, a porous, grainy structure is formed, and the soil is called loam . They have the advantages of the two extreme types of soil and none of their disadvantages. Medium- and fine-textured soils (clays, loams, silts) are usually more suitable for plant growth due to their content in sufficient quantities. nutrients and ability to retain water.

In soil, as a rule, three main horizons are distinguished, differing in morphological and chemical properties:

1. Upper humus-accumulative horizon (A), in which organic matter accumulates and transforms and from which some of the compounds are carried down by washing waters.

2. Washing horizon or illuvial (B), where the substances washed from above settle and are transformed.

3. Mother breed or horizon (C), the material of which is converted into soil. Within each horizon, more subdivided layers are distinguished, which also differ greatly in properties.

Soil is the environment and the main condition for the development of plants. Plants take root in the soil and from it they draw all the nutrients and water they need for life. The term soil means the topmost layer of solid earth's crust, suitable for processing and growing plants, which in turn consists of fairly thin moisturized and humus layers.

The moistened layer is dark in color, has a slight thickness of several centimeters, contains greatest number soil organisms, there is vigorous biological activity in it.

The humus layer is thicker; if its thickness reaches 30 cm, we can talk about very fertile soil; it is home to numerous living organisms that process plant and organic residues into mineral components, as a result of which they are dissolved by groundwater and absorbed by plant roots. Below are the mineral layer and source rocks.

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Soil – This is a thin layer of the land surface, processed by the activity of living organisms.

The diversity of natural conditions on Earth has led to the formation of a heterogeneous soil cover with a certain pattern of changing soil types according to natural areas and in connection with altitudinal zonation. At any point in the area, the soil is also heterogeneous and is characterized by the differentiation of phyla into more or less clearly defined genetic horizons. The differentiated soil profile is shown in Fig. 1

Fig. 1 Scheme of the soil profile structure: A1-humus-accumulative horizon; A2 – eluvial horizon; A2B – eluvial-illuvial horizon; B – illuvial horizon; C – mother breed

For formation certain type soil and soil profile are influenced by climate, parent rocks that underlie it, relief, nature of water exchange processes, type natural vegetation, characteristic for this climate zone, animals and microorganisms living in the soil.

Solid particles are permeated in the soil with pores and cavities, filled partly with air and partly with water, so small particles can also inhabit the soil. aquatic organisms. The volume of small cavities in loose soil can be up to 70%, and in dense soil - about 20%. In these pores and cavities microscopic organisms live– bacteria, fungi, protozoa, roundworms, arthropods. Larger animals make their own passages in the soil.

The soil depth is no more than 1.5-2 m. The air in the soil cavities is enriched in carbon dioxide and depleted in oxygen. In this way, the living conditions in the soil resemble the aquatic environment, but the ratio of water and air in the soil is constantly changing and depends on weather conditions.

Temperature fluctuations in the soil are sharp on the surface, but quickly smooth out with depth.

The main feature of the soil environment is constant supply of organic matter, mainly due to dying plants and falling leaves. It is a valuable source of energy for the organisms living in it, so soil is the richest living environment.

Soil is the most important link in the cycle of substances. It is here that the biological cycle begins and closes here.

Soils act as most powerful filter for water purification, have a high ability to bind chemical elements thanks to its absorption capacity.

The most important property of soil is fertility , those. the ability to ensure the growth and development of plants. This property is of exceptional value for human life and other organisms. The soil is integral part biosphere and energy in nature, maintains the gas composition of the atmosphere.

Soil composition: solid particles, liquid (water), gases (air, O, CO), plants, animals, microorganisms, humus.

Soil thickness; 0.5m - tundra, mountains; 1.5 m - on the plains.

1 cm of soil is formed in about 100 years.

Soil types:

1. Arctic and tundra (humus up to 1-3%)

2. Podzolic (coniferous forests, humus up to 4-5%).

3. Chernozems (steppe, humus up to 10%).

4. Chestnut (in dry steppes, humus up to 4%).

5. Gray-brown (deserts subtropical zones, humus 1-1.5%).

6. Red soils (wet subtropical forest, humus up to 6%).

Humus - soil organic matter, formed as a result of the biochemical decomposition of plant and animal residues, which accumulates in the top layer of soil. Main source plant nutrition. Microelements also accumulate in humus. During soil exploitation, the amount of humus decreases, so it is necessary to apply various fertilizers.

Physical properties:

1. Mechanical composition - the content of particles of different diameters.

2. Density.

3. Heat capacity, thermal conductivity.

4. Moisture capacity, moisture permeability (sand has higher moisture permeability, clay has higher moisture capacity).

5. Aeration - the ability to saturate the soil with air (loosening the soil).

Chemical properties:

1. Chemical composition:

2. Acidity

Influence acidity for plants:

They live on acidic soils (pH< 6,7) карликовая береза, хвощ, некоторые мхи

Neutral (pH 6.7 - 7.0) most cultivated plants

On alkaline soils (pH > 7.0) steppe and desert plants (quinoa, wormwood)

Can grow on any soil (lily of the valley, loach, wild strawberry)

Soil habitat.

Characteristic

Adaptation of the body to the environment

Soil

Created by the Living

organisms. Getting used to it
simultaneously with ground -
air environment. Shortage
or complete absence
Sveta. High density.
Has 4 phases: solid,
liquid, gaseous,

living organisms.

Heterogeneous in

space.

The body has mucous membranes
integument or smooth
surface, near

some have a digging apparatus and developed muscles. Many are characterized by microscopic or small sizes.

Human impacts on soils are associated with the destruction of natural landscapes, depletion of species diversity, and a decrease in the stability, productivity and biomass of ecosystems.

Maintaining and increasing fertility requires a large investment of energy in the form of fertilizers, tillage, weed and pest control.

Usually there are 4 main reasons for the damage and destruction of lands. These include erosion, negative consequences irrigation, soil depletion and alienation.

Under erosion soils understand their destruction as a result of exposure to water or wind. Over the past 50 years, erosion into the ocean has increased approximately 8 times. Together with the soil, so many nutrients are removed, which is 1.5-2 times higher than those added with fertilizers. Erosion begins primarily where natural vegetation cover, which has two functions, is destroyed:

1) plants hold the soil together with their roots

2) sharply reduces the intensity and strength of water and air flows.

Erosion can be water or wind.

Wind erosion It is most pronounced on light soils. Erosion is enhanced by dry soil and poor humus. Wind erosion is most often observed in steppes, semi-deserts and deserts.

Water erosion manifests itself everywhere, but most strongly in those areas where significant amounts of precipitation fall against the background of large open spaces with intensive soil cultivation, that is, in forest, forest-steppe and steppe zones.

Erosion control measures include:

1) reducing the load on ecosystems;

2) compliance with grazing standards for livestock on pastures;

3) compliance with recreational loads;

4) protection of arable land (proper plowing, creation of shelterbelts, application of fertilizers).

Problems of irrigated agriculture. The area of irrigated land in the world is about 250 million hectares. Except water erosion, irrigated soils are exposed salinization. The fact is that more water is supplied to the fields than necessary. This moisture penetrates groundwater and increases their level. Groundwater begins to evaporate intensively, and the salts dissolved in it accumulate on the surface. These soils are unsuitable for farming, so watering should be moderate.

Land depletion. The causes of depletion are: removal of nutrients from the crop, loss of humus, deterioration water regime etc. The results of soil depletion are loss of fertility and desertification. Soil depletion is primarily due to the loss of humus. Over the past 70 years, its content has decreased from 3.5-4% to 2-3%. Greatest losses humus are observed on chernozems.

Alienation of lands – This is their removal and use for various purposes not related to the production of plant products, most often for the construction of cities, roads, airfields, waste storage, mining, etc.

Use of fertilizers and pesticides.

Incorrect and irrational use mineral fertilizers leads to increased soil acidity, changes species composition soil organisms.

Pesticides– a group of substances that are used to destroy or reduce the number of organisms undesirable for humans. Used to destroy plants herbicides, insects – insecticides, mushrooms – fungicides. The harmfulness of pesticides depends on their toxicity, life expectancy, and ability to transform in the environment.

4.3. Soil as a habitat

4.3.1. Soil Features

The soil is a loose thin surface layer of land in contact with the air. Despite its insignificant thickness, this shell of the Earth plays a vital role in the spread of life. The soil is not just solid, like most rocks of the lithosphere, but a complex three-phase system in which solid particles are surrounded by air and water. It is permeated with cavities filled with a mixture of gases and aqueous solutions, and therefore extremely diverse conditions develop in it, favorable for the life of many micro- and macroorganisms (Fig. 49). The soil is smoothed temperature fluctuations compared to the ground layer of air, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a humidity regime intermediate between water and terrestrial environment. The soil concentrates reserves of organic and mineral substances supplied by dying vegetation and animal corpses. All this determines the greater saturation of the soil with life.

The root systems of terrestrial plants are concentrated in the soil (Fig. 50).

Rice. 49. Underground passages of Brandt’s vole: A – top view; B – side view

N. M. Chernova, A. M. Bylova. "General Ecology"

Rice. 50. Placement of roots in steppe chernozem soil (according to M. S. Shalyt, 1950)

On average, per 1 m2 of soil layer there are more than 100 billion protozoan cells, millions of rotifers and tardigrades, tens of millions of nematodes, tens and hundreds of thousands of mites and springtails, thousands of other arthropods, tens of thousands of enchytraeids, tens and hundreds

earthworms, mollusks and other invertebrates. In addition, 1 cm2 of soil contains tens and hundreds of millions of bacteria, microscopic fungi, actinomycetes and other microorganisms. The illuminated surface layers contain hundreds of thousands of photosynthetic cells of green, yellow-green, diatoms and blue-green algae in every gram. Living organisms are just as characteristic of the soil as its nonliving components. Therefore, V.I. Vernadsky classified the soil as a bio-inert body of nature, emphasizing its saturation with life and its inextricable connection with it.

The heterogeneity of soil conditions is most pronounced in the vertical direction. With depth, a number of the most important environmental factors affecting the life of soil inhabitants. First of all, this relates to the structure of the soil. It contains three main horizons, differing in morphological and chemical properties: 1) the upper humus-accumulative horizon A, in which organic matter accumulates and is transformed and from which some of the compounds are carried down by washing waters; 2) the influx horizon, or illuvial B, where the substances washed out from above settle and are transformed, and 3) the parent rock, or horizon C, the material of which is transformed into soil.

N. M. Chernova, A. M. Bylova. "General Ecology"

Within each horizon, more subdivided layers are distinguished, which also differ greatly in properties. For example, in the area temperate climate under conifers or mixed forests horizon A consists of litter (A 0 ) - a layer of loose accumulation of plant matter

residues, a dark-colored humus layer (A 1), in which particles of organic origin are mixed with mineral ones, and a podzolic layer (A 2) - ash-gray in

color in which silicon compounds predominate, and all soluble substances washed into the depths of the soil profile. Both the structure and chemistry of these layers are very different, and therefore plant roots and soil inhabitants, moving just a few centimeters up or down, find themselves in different conditions.

The sizes of cavities between soil particles suitable for animals to live in usually decrease rapidly with depth. For example, in meadow soils the average diameter of cavities at a depth of 0–1 cm is 3 mm, at 1–2 cm – 2 mm, and at a depth of 2–3 cm – only 1 mm; deeper the soil pores are even smaller. Soil density also changes with depth. The loosest layers are those containing organic matter. The porosity of these layers is determined by the fact that organic substances glue mineral particles into larger aggregates, the volume of cavities between which increases. The most dense is usually the illuvial horizon, cemented by colloidal particles washed into it.

Moisture in the soil is present in various states: 1) bound (hygroscopic and film) firmly held by the surface of soil particles; 2) capillary occupies small pores and can move along them in different directions; 3) gravitational fills larger voids and slowly seeps down under the influence of gravity; 4) vaporous is contained in the soil air.

Water content varies in different soils and different times. If there is too much gravitational moisture, then the soil regime is close to the regime of reservoirs. In dry soil only bound water and conditions are approaching those on land. However, even in the driest soils, the air is moister than the ground air, so the inhabitants of the soil are much less susceptible to the threat of drying out than on the surface.

The composition of soil air is variable. With depth, the oxygen content in it decreases greatly and the concentration increases carbon dioxide. Due to the presence of decomposing substances in the soil organic matter the soil air may contain a high concentration of toxic gases such as ammonia, hydrogen sulfide, methane, etc. When the soil is flooded or intensive rotting of plant residues, completely anaerobic conditions may occur in some places.

Fluctuations in cutting temperature only on the soil surface. Here they can be even stronger than in the surface layer of air. However, with each centimeter in depth, daily and seasonal temperature changes become less and less and at a depth of 1–1.5 m they are practically no longer traceable (Fig. 51).

N. M. Chernova, A. M. Bylova. "General Ecology"

Rice. 51. Decrease in annual fluctuations in soil temperature with depth (according to K. Schmidt-Nilsson, 1972). The shaded part is the range of annual temperature fluctuations

All these features lead to the fact that, despite the great heterogeneity of environmental conditions in the soil, it acts as a fairly stable environment, especially for mobile organisms. The steep gradient of temperature and humidity in the soil profile allows soil animals to provide themselves with a suitable ecological environment through minor movements.

4.3.2. Soil inhabitants

The heterogeneity of the soil leads to the fact that for organisms different sizes she acts as different environment. For microorganisms special meaning has a huge total surface of soil particles, since the overwhelming majority of the microbial population is adsorbed on them. The complexity of the soil environment creates a wide variety of conditions for a wide variety of functional groups: aerobes and anaerobes, consumers of organic and mineral compounds. The distribution of microorganisms in the soil is characterized by fine focality, since even within a few millimeters different ecological zones can change.

For small soil animals (Fig. 52, 53), which are grouped under the name microfauna (protozoa, rotifers, tardigrades, nematodes, etc.), the soil is a system of microreservoirs. Essentially, these are aquatic organisms. They live in soil pores filled with gravitational or capillary water, and part of life can, like microorganisms, be in an adsorbed state on the surface of particles in thin layers of film moisture. Many of these species also live in ordinary bodies of water. However, soil forms are much smaller than freshwater ones and, in addition, are distinguished by their ability to remain in an encysted state for a long time, waiting out unfavorable periods. While freshwater amoebas have sizes of 50-100 microns, soil ones - only 10-15. Representatives of flagellates are especially small, often only 2–5 microns. Soil ciliates also have dwarf sizes and besides, they can greatly change the shape of the body.

N. M. Chernova, A. M. Bylova. "General Ecology"

Rice. 52. Testate amoebas feeding on bacteria on decaying leaves of the forest floor

Rice. 53. Soil microfauna (according to W. Dunger, 1974):

1–4 – flagella; 5–8 – naked amoebas; 9-10 – testate amoebas; 11–13 – ciliates; 14–16 – roundworms; 17–18 – rotifers; 19–20 – tardigrades

To slightly larger air-breathing animals, the soil appears as a system of small caves. Such animals are grouped under the name mesofauna (Fig. 54).

N. M. Chernova, A. M. Bylova. "General Ecology"

The sizes of soil mesofauna representatives range from tenths to 2–3 mm. This group includes mainly arthropods: numerous groups of mites, primary wingless insects (collembolas, proturus, two-tailed insects), small species of winged insects, symphila centipedes, etc. They do not have special adaptations for digging. They crawl along the walls of soil cavities using their limbs or wriggling like a worm. Soil air saturated with water vapor allows breathing through the covers. Many species do not have a tracheal system. Such animals are very sensitive to drying out. Their main means of escape from fluctuations in air humidity is to move deeper. But the possibility of deep migration through soil cavities is limited by a rapid decrease in pore diameter, so movement through soil holes is accessible only to the smallest species. Larger representatives of the mesofauna have some adaptations that allow them to tolerate a temporary decrease in soil air humidity: protective scales on the body, partial impermeability of the integument, a solid thick-walled shell with an epicuticle in combination with a primitive tracheal system that ensures respiration.

Rice. 54. Soil mesofauna (no W. Danger, 1974):

1 – false scorion; 2 – gama new klesha; 3–4 oribatid mites; 5 – pauroiod centipede; 6 – chironomid mosquito larva; 7 – beetle from the family. Ptiliidae; 8–9 springtails

Representatives of the mesofauna survive periods of soil flooding in air bubbles. Air is retained around the body of animals due to their non-wettable integument, which is also equipped with hairs, scales, etc. The air bubble serves as a kind of “physical gill” for a small animal. Respiration is carried out due to oxygen diffusing into the air layer from the surrounding water.

Representatives of micro- and mesofauna are able to tolerate winter freezing of the soil, since most species cannot move down from layers exposed to negative temperatures.

Larger soil animals, with body sizes from 2 to 20 mm, are called representatives of macrofauna (Fig. 55). These are insect larvae, millipedes, enchytraeids, earthworms etc. For them, soil is a dense medium that provides significant mechanical resistance when moving. These are relatively large forms move in the soil either by expanding natural wells by pushing apart soil particles, or by digging new passages. Both modes of movement leave their mark on external structure animals.

N. M. Chernova, A. M. Bylova. "General Ecology"

Rice. 55. Soil macrofauna (no W. Danger, 1974):

1 – earthworm; 2 – woodlice; 3 – labiopodal centipede; 4 – two-legged centipede; 5 – ground beetle larva; 6 – click beetle larva; 7 – mole cricket; 8 – beetle larva

The ability to move through thin holes, almost without resorting to digging, is inherent only in species that have a body with a small cross-section, capable of bending strongly in winding passages (centipedes - drupes and geophiles). By pushing apart soil particles due to the pressure of the body walls, earthworms and centipede mosquito larvae move

And etc. Having fixed the rear end, they thin and lengthen the front, penetrating into narrow soil crevices, then secure the front part of the body and increase its diameter. In this case, in the expanded area, due to the work of the muscles, a strong hydraulic pressure of the non-compressible intracavitary fluid is created: in worms - the contents of the coelomic sacs, and in tipulids - the hemolymph. Pressure is transmitted through the body walls to the soil, and thus the animal expands the well. At the same time, the rear passage remains open, which threatens to increase evaporation and persecution of predators. Many species have developed adaptations to an ecologically more advantageous type of movement in the soil - digging and blocking the passage behind them. Digging is carried out by loosening and raking away soil particles. The larvae of various insects use for this purpose the anterior end of the head, mandibles and forelimbs, expanded and reinforced with a thick layer of chitin and spines.

And outgrowths. At the posterior end of the body, devices for strong fixation develop

– retractable supports, teeth, hooks. To close the passage on the last segments, a number of species have a special depressed platform framed by chitinous sides or teeth, a kind of wheelbarrow. Similar areas are formed on the back of the elytra and in bark beetles, which also use them to clog passages with drill flour. Closing the passage behind them, the animals that inhabit the soil are constantly in a closed chamber, saturated with the vapors of their own bodies.

Gas exchange of most species of this ecological group is carried out with the help of specialized respiratory organs, but at the same time it is supplemented by gas exchange through the integument. It is even possible to perform exclusively cutaneous respiration, for example in earthworms and enchytraeids.

Burrowing animals can leave layers where unfavorable conditions arise. During drought and winter, they concentrate in deeper layers, usually several tens of centimeters from the surface.

Soil megafauna are large diggers, mainly mammals. A number of species spend their entire lives in the soil (mole rats, mole rats, zokora, Eurasian moles, golden moles

N. M. Chernova, A. M. Bylova. "General Ecology"

Africa, marsupial moles of Australia, etc.). They create entire systems of passages and burrows in the soil. Appearance and the anatomical features of these animals reflect their adaptation to a burrowing underground lifestyle. They have underdeveloped eyes, a compact, ridged body with a short neck, short thick fur, strong digging limbs with strong claws. Mole rats and mole rats loosen the ground with their incisors. Soil megafauna should also include large oligochaetes, especially representatives of the family Megascolecidae, living in the tropics and Southern Hemisphere. The largest of them is Australian Megascolides australis reaches a length of 2.5 and even 3 m.

In addition to the permanent inhabitants of the soil, among large animals we can distinguish a large environmental group burrow inhabitants (gophers, marmots, jerboas, rabbits, badgers, etc.). They feed on the surface, but reproduce, hibernate, rest, and escape danger in the soil. A number of other animals use their burrows, finding in them a favorable microclimate and shelter from enemies. Burrowers have structural features characteristic of terrestrial animals, but have a number of adaptations associated with the burrowing lifestyle. For example, badgers have long claws and strong muscles on the forelimbs, a narrow head, and small ears. Compared to hares that do not dig holes, rabbits have noticeably shortened ears and hind legs, a more durable skull, more developed bones and muscles of the forearms, etc.

For a number of ecological features, soil is a medium intermediate between aquatic and terrestrial. WITH aquatic environment The soil is brought together by its temperature regime, the low oxygen content in the soil air, its saturation with water vapor and the presence of water in other forms, the presence of salts and organic substances in soil solutions, and the ability to move in three dimensions.

WITH the soil is brought together by the air environment, the presence of soil air, the threat of drying out

V upper horizons, rather sharp changes temperature regime surface layers.

The intermediate ecological properties of soil as a habitat for animals suggest that soil played a special role in the evolution of the animal world. For many groups, in particular arthropods, soil served as a medium through which initially aquatic inhabitants were able to transition to a terrestrial lifestyle and conquer land. This path of arthropod evolution was proven by the works of M. S. Gilyarov (1912–1985).

The soil is a loose thin surface layer of land in contact with the air. Its most important property is fertility, those. the ability to ensure the growth and development of plants. Soil is not just a solid body, but a complex three-phase system in which solid particles are surrounded by air and water. It is permeated with cavities filled with a mixture of gases and aqueous solutions, and therefore extremely diverse conditions develop in it, favorable for the life of many micro- and macroorganisms. Temperature fluctuations in the soil are smoothed out compared to the surface layer of air, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a moisture regime intermediate between the aquatic and terrestrial environments. Reserves of organic and mineral substances supplied by dying vegetation and animal corpses are concentrated in the soil (Fig. 1.3).

Rice. 1.3.

The soil is heterogeneous in its structure and physical and chemical properties. The heterogeneity of soil conditions is most pronounced in the vertical direction. With depth, a number of the most important environmental factors affecting the life of soil inhabitants change dramatically. First of all, this relates to the structure of the soil. It contains three main horizons, differing in morphological and chemical properties (Fig. 1.4): 1) upper humus-accumulative horizon A, in which organic matter accumulates and is transformed and from which some of the compounds are carried down by leaching waters; 2) the influx horizon, or illuvial B, where the substances washed out from above settle and are transformed, and 3) the parent rock, or horizon C, the material of which is transformed into soil.

Fluctuations in cutting temperature only on the soil surface. Here they can be even stronger than in the surface layer of air. However, with every centimeter deeper, daily and seasonal temperature changes become less and less and at a depth of 1-1.5 m they are practically no longer traceable.

Rice. 1.4.

All these features lead to the fact that, despite the great heterogeneity of environmental conditions in the soil, it acts as a fairly stable environment, especially for mobile organisms. All this determines the greater saturation of the soil with life.

The root systems of land plants are concentrated in the soil. In order for plants to survive, the soil as a habitat must satisfy their need for mineral nutrients, water and oxygen, while pH values (relative acidity and salinity (salt concentration) are important).

1. Mineral nutrients and the ability of the soil to retain them. The following mineral nutrients are necessary for plant nutrition: (biogens), like nitrates (N0 3), phosphates ( P0 3 4),

potassium ( TO+) and calcium ( Ca 2+). With the exception of nitrogen compounds that are formed from atmospheric N 2 during the cycle of this element, all mineral nutrients are initially included in chemical composition rocks along with “non-nutrient” elements such as silicon, aluminum and oxygen. However, these nutrients are inaccessible to plants while they are fixed in the rock structure. In order for nutrient ions to move into a less bound state or into an aqueous solution, the rock must be destroyed. The breed called maternal, destroyed during the process of natural weathering. When nutrient ions are released, they become available to plants. Being the initial source of nutrients, weathering is still too slow a process to ensure normal plant development. In natural ecosystems, the main source of nutrients is decomposing detritus and metabolic waste of animals, i.e. nutrient cycle.

In agroecosystems, nutrients are inevitably removed from the harvested crop, since they are part of the plant material. Their stock is regularly replenished by adding fertilizers

2. Water and water holding capacity. Moisture in the soil is present in various states:
1) bound (hygroscopic and film) is firmly held by the surface of soil particles;
2) capillary occupies small pores and can move along them in different directions;
3) gravitational fills larger voids and slowly seeps down under the influence of gravity;
4) vaporous is contained in the soil air.

If there is too much gravitational moisture, then the soil regime is close to the regime of reservoirs. In dry soil, only bound water remains and conditions approach those of land. However, even in the driest soils, the air is moister than the ground air, so the inhabitants of the soil are much less susceptible to the threat of drying out than on the surface.

There are thin pores in the leaves of plants through which carbon dioxide (CO2) is absorbed and oxygen (02) is released during photosynthesis. However, they also allow water vapor from the wet cells inside the leaf to pass out. To compensate for this loss of water vapor from leaves, called transpiration, at least 99% of all water absorbed by the plant is necessary; Less than 1% is spent on photosynthesis. If there is not enough water to replenish losses due to transpiration, the plant withers.

Obviously, if rainwater flows down the surface of the soil rather than being absorbed, there will be no benefit from it. Therefore it is very important infiltration, those. absorption of water from the soil surface. Since the roots of most plants do not penetrate very deeply, water that penetrates deeper than a few centimeters (and for small plants, to a much shallower depth) becomes inaccessible. Therefore, during the period between rains, plants depend on the supply of water held by the surface layer of soil, like a sponge. The amount of this reserve is called water holding capacity of the soil. Even with infrequent rainfall, soils with good water-holding capacity can store enough moisture to support plant life over a fairly long dry period.

Finally, the water supply in the soil is reduced not only as a result of its use by plants, but also due to evaporation from the soil surface.

So, the ideal soil would be one with good infiltration and water-holding capacity and a cover that reduces water loss through evaporation.

3. Oxygen and aeration. To grow and absorb nutrients, roots need energy generated by the oxidation of glucose during cellular respiration. This consumes oxygen and produces carbon dioxide as a waste product. Consequently, ensuring the diffusion (passive movement) of oxygen from the atmosphere into the soil and the reverse movement of carbon dioxide is another important feature of the soil environment. They call him aeration. Typically, aeration is hampered by two circumstances that lead to slower growth or death of plants: soil compaction and saturation with water. Seal called the approach of soil particles to each other, in which the air space between them becomes too limited for diffusion to occur. Water saturation - the result of waterlogging.

The loss of water by the plant during transpiration must be compensated by reserves of capillary water in the soil. This reserve depends not only on the abundance and frequency of precipitation, but also on the ability of the soil to absorb and retain water, as well as on direct evaporation from its surface when the entire space between soil particles is filled with water. This can be called "flooding" the plants.

Respiration of plant roots is the absorption of oxygen from environment and the release of carbon dioxide into it. In turn, these gases must be able to diffuse between soil particles

4. Relative acidity (pH). Most plants and animals require a close to neutral pH = 7.0; in the majority natural environments habitat such conditions are met.
5. Salt and osmotic pressure. For normal functioning, the cells of a living organism must contain a certain amount of water, i.e. require water balance. However, they themselves are not able to actively pump or pump out water. Their water balance is regulated by the ratio - the concentration of salts on the outer and inner sides of the cell membrane. Water molecules are attracted to salt ions. Cell membrane prevents the passage of ions, and water quickly moves through it in the direction of greater concentration. This phenomenon is called osmosis.

Cells control their water balance by regulating internal salt concentration, and water flows in and out by osmosis. If the salt concentration outside the cell is too high, water cannot be absorbed. Moreover, under the influence of osmosis it will be drawn out of the cell, which will lead to dehydration and death of the plant. Highly saline soils are practically lifeless deserts.

Inhabitants of the soil. The heterogeneity of the soil leads to the fact that for organisms of different sizes it acts as a different environment.

For small soil animals, which are grouped under the name microfauna(protozoa, rotifers, tardigrades, nematodes, etc.), soil is a system of micro-reservoirs. Essentially, these are aquatic organisms. They live in soil pores filled with gravitational or capillary water, and part of life can, like microorganisms, be in an adsorbed state on the surface of particles in thin layers of film moisture. Many of these species also live in ordinary bodies of water. However, soil forms are much smaller than freshwater ones, and, in addition, falling into unfavorable conditions environment, they secrete a dense shell on the surface of their body - cyst(Latin cista - box), protecting them from drying out, exposure harmful substances etc. At the same time, physiological processes slow down, animals become motionless, take on a rounded shape, stop feeding, and the body falls into a state hidden life(encysted state). If the encysted individual again finds itself in favorable conditions, excystation occurs; the animal leaves the cyst, turns into a vegetative form and resumes active life.

To slightly larger air-breathing animals, the soil appears as a system of small caves. Such animals are grouped under the name mesofauna. The sizes of soil mesofauna representatives range from tenths to 2-3 mm. This group includes mainly arthropods: numerous groups of mites, primary wingless insects (for example, two-tailed insects), small species of winged insects, symphila centipedes, etc.

Larger soil animals, with body sizes from 2 to 20 mm, are called representatives macrofauna. These are insect larvae, centipedes, enchytraeids, earthworms, etc. For them, the soil is a dense medium that provides significant mechanical resistance when moving.

Megafauna soils are large shrews, mainly mammals. A number of species spend their entire lives in the soil (mole rats, mole rats, marsupial moles of Australia, etc.). They create entire systems of passages and burrows in the soil. The appearance and anatomical features of these animals reflect their adaptability to a burrowing underground lifestyle. They have underdeveloped eyes, a compact, ridged body with a short neck, short thick fur, strong digging limbs with strong claws.

In addition to the permanent inhabitants of the soil, a large ecological group can be distinguished among large animals burrow inhabitants(gophers, marmots, jerboas, rabbits, badgers, etc.). They feed on the surface, but reproduce, hibernate, rest, and escape danger in the soil.

For a number of ecological features, soil is a medium intermediate between aquatic and terrestrial. The soil is similar to the aquatic environment due to its temperature regime, low oxygen content in the soil air, its saturation with water vapor and the presence of water in other forms, the presence of salts and organic substances in soil solutions, and the ability to move in three dimensions.

The soil is brought closer to the air environment by the presence of soil air, the threat of drying out in the upper horizons, and rather sharp changes in the temperature regime of the surface layers.

The intermediate ecological properties of soil as a habitat for animals suggest that soil played a special role in the evolution of the animal world. For many groups, in particular arthropods, soil served as a medium through which initially aquatic inhabitants were able to transition to a terrestrial lifestyle and conquer land. This path of arthropod evolution has been proven by the works of M.S. Gilyarov (1912-1985).

Table 1.1 shows comparative characteristics abiotic environments and adaptation of living organisms to them.

Characteristics of abiotic environments and adaptation of living organisms to them

Table 1.1

Wednesday	Characteristic	Adaptation of the body to the environment
	The most ancient. Illumination decreases with depth. When diving, for every 10 m, the pressure increases by one atmosphere. Oxygen deficiency. The degree of salinity increases from fresh water to marine and oceanic. Relatively uniform (homogeneous) in space and stable in time	Streamlined body shape, buoyancy, mucous membranes, development of air cavities, osmoregulation
Soil	Created by living organisms. She mastered the ground-air environment simultaneously. Deficiency or complete absence of light. High density. Four-phase (phases: solid, liquid, gaseous, living organisms). Inhomogeneous (heterogeneous) in space. Over time, conditions are more constant than in the terrestrial-air habitat, but more dynamic than in the aquatic and organismal environment. The richest habitat for living organisms	The body shape is valval (smooth, round, cylindrical or spindle-shaped), mucous membranes or a smooth surface, some have a digging apparatus and developed muscles. Many groups are characterized by microscopic or small sizes as an adaptation to life in film water or in air-bearing pores
Ground-based	Sparse. Abundance of light and oxygen. Heterogeneous in space. Very dynamic over time	Development of the supporting skeleton, mechanisms for regulating the hydrothermal regime. Freeing the sexual process from the liquid medium