Since the formation of the Earth, processes of transition of chemical compounds and elements from one state to another have been taking place on the planet. This is the cycle of substances in nature. How it happens and why it is needed will be discussed in this article.
Quick navigation through the article
They are so different
The cycle of substances is, in fact, essentially an endlessly repeating cycle. And thanks to the interaction chemical elements and the variety of chemical compounds they are never repeated exactly. Let's consider different types of cycles, as well as how the closed cycle of substances affects the development and existence of our planet.
Biogeochemical cycle of substances
What is the role of energy in the cycle? The primary source of energy for the cycle of substances in most cases is the Sun. This energy is drawn in from space.
Cycle of matter and energy
The energy produced by organisms is converted into heat and lost to the ecosystem. In contrast, the movement of substances occurs through self-regulating processes with the participation of all components of various ecosystems. Of the more than 95 elements found in nature, only 40 are needed for the life of living organisms. Among them, the most important and necessary in huge quantities are four basic elements:
- oxygen;
- hydrogen;
- carbon;
- nitrogen.
Where do they come from in the required size? For example, nitrogen is taken from the atmosphere by active nitrogen-fixing bacteria, then returned by other bacteria. Oxygen, used by various organisms for respiration, comes into the atmosphere through photosynthesis. Plants absorb carbon dioxide, involving it in the cycle of substances. Carbon and hydrogen also participate in important processes.
In nature, nothing happens for nothing. Let's look at volcanoes. During their eruption, various gases, including nitrogen, enter the atmosphere. This is the cycle of gaseous substances.
In the activity of evolution in the biosphere, the number of biological components. Recently, humans have played an important role in these processes. Through its activities, it enhances the circulation of substances and the flow of energy in the ecosystem that has developed over thousands of years. This has a destructive effect on the biosphere that has developed at the moment.
Previously, when life was just beginning on Earth, there was more carbon in the atmosphere, but there was almost no oxygen. Therefore, the first living organisms were anaerobic. Over a long period of time, oxygen accumulated and the percentage of carbon decreased. Now the amount of carbon dioxide is increasing. This is facilitated by the use of fossil fuels and the reduction of the “lungs of the planet” - jungles and forests. The anthropogenic cycle of substances is losing its isolation.
Studying in which zones of the Earth the cycles of matter and energy are most active, scientists came to the conclusion that tropical ecosystems are more conservative in this regard. When studying the human influence on these processes, we need to talk not about the fact that people, through their activities, change something that should not change, but about the fact that this activity affects the rate of change.
In the description of the cycle of substances, an ascending part and a descending part are sometimes distinguished. During the cycle of substances, the energy contained in organic substances, passing from one state to another, is gradually lost. This is the downward part. When substances can no longer serve as a source of energy, they become material for new cells. This is the ascending part of the circuit.
Big and small
There are two main circuits. The large geological cycle of substances began from the moment the planet was formed. The cycle in it can last thousands of years. Under the influence of external factors, rocks are destroyed, their smallest particles remain on land, some of them with water enter the World Ocean, where, in turn, new strata are formed. Thanks to geotectonic processes, movement and changes in the bottom topography, these layers again end up on land and everything starts all over again. The geological cycle of substances is determined by the interaction of two energies: the Earth and the Sun. It is possible only if all components are present.
Geological cycle of substances A small cycle of substances in nature is always part of a large one. It is called the biogeochemical cycle of substances and manifests itself only within the boundaries of the biosphere, being present in all ecosystems. During it nutrients, carbon and water accumulate in plants, then are spent on the growth of not only the plants themselves, but also on the vital activity of other organisms. As a rule, these are animals that eat plants - consumers. The products of the vital activity and decay of these animals under the influence of microorganisms are again decomposed into mineral components and, with the help of plants, are again brought into circulation. All chemical elements, primarily necessary for the construction of living cells, participate in such cycles.
The most mobile
Water never stands still. Evaporating from various surfaces, it accumulates in the atmosphere in order to fall to the ground in the form of precipitation. At the same time, it constantly changes its shape. Therefore, the amount of water does not change - it is constantly renewed. This is the water cycle in nature. It connects the geological and biotic cycle of substances.
Water cycle in nature In the biosphere, water, changing its state, goes through small and large circulations. Evaporation from the ocean surface, condensation in the atmosphere, and precipitation back into the ocean is a small turnover. When some of the water vapor is transferred from the ocean to land by air currents, this water participates in a large circulation. Some of it evaporates and remains in the atmosphere, the rest, along with streams, rivers and groundwater, ends up back into the ocean. This completes the big cycle and starts all over again.
Most active
Within the boundaries of the biosphere, there is a continuous instantaneous exchange of oxygen from the air with living organisms, which serves as the main source of life. It is very complex, entering into various combinations of mineral and organic substances. At the present moment in the development of the biosphere, a period has come when the amount of oxygen released is almost equal to the amount absorbed. Carbon is included in the cycle of substances due, among other things, to photosynthesis. Synthesis and its components are the basis for air renewal in the biosphere.
Oxygen cycle in nature Essential Nitrogen
During the decay of organic matter, part of the nitrogen contained in them is converted into ammonia, which is processed by plants living in the soil back into nitric acid. It enters into a micro-reaction with the organisms contained in the soil and is converted into nitrates. This is a form accessible to plants. This creates a small nitrogen cycle.
Nitrogen cycle However, some nitrogen is released into the atmosphere during decay and forms free nitrogen. In addition, this form appears due to the combustion of organic substances, the burning of coal, and firewood.
Do not allow the natural balance of azotobacter to be disturbed. Some of them live on the roots of legumes, forming small tubers. By releasing atmospheric nitrogen from the air, they convert it into nitrogen compounds, which are transferred to plants. Later, plants transform them into proteins, fats, carbohydrates and other substances. This is how the nitrogen cycle occurs.
By using plants without allowing them to go through the stage of decay, people create a nitrogen deficiency. To avoid this, people have learned to add nitrogen fertilizers to the soil, thereby compensating nature for the lost balance.
Essential sulfur
Its importance in the cycle is invaluable. Sulfur serves as a source of energy for sulfur bacteria, without which water purification is impossible. In nature, these bacteria are widespread. It is an important component in the construction of many types of proteins. The cycle of substances in the earth's crust also cannot do without sulfur. The contribution of sulfur to the large cycle of substances is the microorganisms that feed on it and convert amino acids. The main anthropogenic suppliers of sulfur into the large cycle of substances are decomposing plants and animal organisms. They release sulfur gas. This completes the sulfur cycle.
Sulfur cycle Biosphere
All representatives of living nature, including humans, form biomass. It is constantly changing, participating in processes occurring in the environment.
Plants are called producers, animals are called consumers. Protozoa and other microorganisms that decompose organic matter into inorganic matter are called decomposers. They are also called destroyers.
The process of decomposition is the destruction of organic matter.
Let's figure out what role representatives play in the cycle of substances different groups and what is the role of producers:
- blue-green bacteria and plants convert sunlight into energy chemical bonds. In this way, organic matter is born from inorganic elements;
- omnivores that can eat plants. This includes humans. They consume plants (organic matter), processing them internally and producing inorganic matter at the output;
- carnivores eat herbivores, organic matter also enters them, but not by plants, but in a different form;
- apex predators capable of feeding on carnivores. This is the last movement of organic matter within living organisms;
- protozoa, fungi and microorganisms that decompose the remains of living beings. During this process, they convert organic matter into inorganic form - salts, water, minerals and carbon dioxide;
- all these elements are used again by plants.
In the cycle of substances, microorganisms play the largest role; destroyers are considered the initial link of the phenomenon.
As can be seen from this diagram, consumers in the process of cycling substances in the biosphere use food connections, an important component of the chain. However, everything starts with plants and ends with them.
Diversity of plants in nature In addition to the closed cycle, there is also an open cycle of substances.
Ecosystems
In short, ecosystems are natural complexes, formed by the environment habitat and the totality of organisms (biocenoses) living in it. They are a component that ensures the circulation of substances in the biosphere. They are studied by a science called ecology.
People of different professions work in this field. Currently, the global cycle of substances is disrupted by human actions due to the destructive activities of anthropogenic influence.
Ecosystems undergo many biochemical cycles during their development. Moreover, if the cycle is not closed, then one ecosystem can transform into another over time. This situation is influenced by the circulation of substances in the biocenosis.
Let's consider how the cycle of substances and the transformation of energy are based in ecosystems of various types.
Meadow
Various vegetation: grass, flowers, small plants are producers. Flying and crawling insects feed on grass and pollen. Birds feed on these insects. After their death, decomposers deal with the remains, and the products of the latter’s activity become constituent elements of new producers, plants. It turns out that consumers in the meadow ecosystem participate in the cycle of substances and the transformation of organic matter into inorganic matter.
Lake
Each lake has its own ecosystem. The producers here are plankton and duckweed, which, in addition to the function of processing organic matter, fill the water with oxygen. There are a lot of consumers or consumers. These are plant-eating fish, crustaceans, tadpoles and larvae. They are followed by predatory fish and waterfowl. Sooner or later, some of them end up at the bottom in the form of remains, and then small invertebrates and bacteria, decomposers, take over them. Since there are much more decomposers in lakes than consumers, they cannot process all the remains that end up on the bottom. This results in an open cycle of substances and energy flow in the ecosystem. If the circuit is not completely closed, then the conditions in the ecosystem gradually change. This is why small lakes eventually turn into swamps.
Cycle of substances in the lake ecosystem The circulation of substances in an aquarium follows the same pattern.
Swamp
When the lake begins to overgrow, moss appears near the shores - sphagnum. With its appearance, the cycle of substances in the swamp begins. Since sphagnum floats on the surface, a very cold layer of water without oxygen forms underneath it, in which microorganisms cannot exist. Moss branches die and sink to the bottom, forming peat. The thickness of the peat cushion reaches 5 meters - this is where the inhabitants of the swamps live. Since the cycle of substances in the swamp is also not closed, after many, many years the swamp turns into a forest, which explains the constant formation and then overgrowing of swamps. But until this happens, the swamp maintains the groundwater level and is a necessary component in the circulation of substances in the biosphere.
Technogenic cycle of substances
The difference between the technogenic cycle and the biotic cycle is that it is always open. It's more of a resource cycle. This does not have the best effect on the standard of living of various organisms within the biosphere. For example, the rate of decrease in water volume in such a cycle is much greater than in the biotic one. The same can be said about other elements consumed in the process. This data depends on the level of the organization.
Conclusion
The sun is a source of energy that ensures the circulation of substances. It supplies the planet with renewable energy, which in turn is constantly being transformed. There are many cycles that are being studied by scientists for the first time. Even knowing the principles of circulation cycles, experts come to ever new conclusions and discoveries. One gets the impression that man does not know even a tenth of those secrets of nature that are hidden from his sight. The quality of life of future generations depends on how quickly we can solve these mysteries. There is only one main conclusion: the circulation of substances and the transformation of energy in the ecosystem is the key to life on the planet. Life on Earth is impossible without a cycle.
Without a cycle, life on earth is impossible The article shows what role the cycles of matter and energy play in the geographic envelope and in the biosphere. Therefore, we think it is clear that wildlife organizations need human protection.
Thanks to food chains, in the ecosystem, along with the movement of energy, various chemical elements are also transported. As with energy flows, driving force The cycle of matter is driven by solar energy. This is due to the fact that the accumulation of certain chemical substances occurs in the biomass of organisms, and, therefore, during the transfer of energy through food chains, the transfer of substances contained in the biomass also occurs. The flow of substances accompanies the flow of energy in the ecosystem, which, in turn, originates from the energy of sunlight. The circulation of chemicals is also determined by the influence of abiotic components of the ecosystem (for example, climatic factors), as well as active human economic activities. Flows of substances in an ecosystem are united by the concept biogeochemical cycle. Biogeochemical cycle - circulation in the biosphere of chemical elements and not organic compounds along characteristic paths from the external environment into organisms and from organisms into external environment. The chemical elements involved in the cycle are not evenly distributed throughout the entire ecosystem. In addition, they can be found in various chemical forms. Therefore, when studying biogeochemical cycles, two parts should be distinguished.
1) Reserve fund - a large mass of slowly moving substances, mostly not associated with organisms. It is concentrated in the earth's crust, atmosphere and hydrosphere. The movement of substances in the reserve fund occurs due to the influence of abiotic factors of the ecosystem.
2) Exchange fund. It is an inorganic substance found in living organisms. It is characterized by the rapid movement of chemical elements between organic and inorganic environments.
By their nature, biogeochemical cycles are also divided into two categories. The first of them is the circulation of gaseous substances with a reserve fund in the atmosphere or hydrosphere. The other is a sedimentary cycle (i.e., the circulation of solids) with a reserve fund in the earth’s crust. The circulation of gaseous substances is distinguished by its ability to maintain certain concentrations of certain gases, and the concentrations will be approximately the same at all points of the atmosphere and hydrosphere. In sedimentary cycles, the flow rate of substances is much lower than in the gaseous cycle, since the bulk of them are concentrated in the earth’s crust, which is characterized by its low mobility and low activity. Because of this, the ability for self-regulation in the sedimentary cycle is not as great as in the case of the circulation of gaseous substances.
The biogeochemical cycle diagram can be depicted in combination with a simplified diagram of the energy flow of the food chain driving the cycle of substances. This scheme is a ring directed from autotrophs to heterotrophs, and then closing on the autotrophs. From this image it is clear that when studying biogeochemical cycles, the main attention is paid to the reserve fund, that is, the part of the cycle that is physically and chemically separated from living organisms.
Scheme of biogeochemical cycle.
When depicting the biogeochemical cycles of individual substances, the emphasis is on the exchange between organisms and the reserve fund, as well as on the routes of movement of substances within the ecosystem. In this regard, any ecosystem can be represented as a series of blocks through which various substances pass, and in which these substances can remain for various periods of time. Mineral cycles in an ecosystem usually involve three blocks: living organisms, dead organic detritus, and available inorganic substances. Examples of biogeochemical cycles include the nitrogen, phosphorus, and sulfur cycles. The concentration of nitrogen and phosphorus in an ecosystem often directly affects the number of organisms in the ecosystem (i.e. they are limiting factors), and the sulfur cycle can serve as a clear illustration of the connections that have developed between the atmosphere, hydrosphere and the earth’s crust.
The reserve fund of the nitrogen cycle is concentrated in the atmosphere. Atmospheric nitrogen, thanks to the activity of nitrogen-fixing bacteria, as well as through atmospheric phenomena, enters the soil or water in the form of compounds with other elements (the so-called nitrates). Nitrogen is then absorbed by producers, and then by consumers. When dead organic matter is decomposed by decomposers and together with animal excrement products, nitrogen-containing ammonia gas accumulates in soil and aquatic environments. Subsequently, under the influence of various bacteria, nitrogen either returns to the atmosphere or ends up in the soil and water as part of nitrates. Moreover, nitrates dissolved in water can settle at the bottom of reservoirs, and in this case the nitrogen contained in them falls out of the cycle of substances.
Diagram of the nitrogen cycle.
Unlike nitrogen, the reserve fund of the phosphorus cycle is rocks and other sediments formed over millions of years. The phosphorus compounds they contain ( phosphates) undergo gradual dissolution, after which phosphorus passes from dissolved phosphates to plants and then to animals. After the decomposition of dead organic matter, the phosphorus contained in it ends up as part of the compounds contained in water and soil, and again enters the exchange pool of the cycle. However, some of the animal remains (primarily bone tissue) eventually combine with phosphate rocks or sediments at the bottom of reservoirs. In the latter case, phosphorus falls out of the biogeochemical cycle. But the return of phosphorus to the cycle occurs in much smaller quantities than the loss from it. Human activities also lead to large losses of phosphorus, which may result in a deficiency of this element in the future.
One of the main features of the sulfur cycle is that its reserve fund is located both in the soil and in the atmosphere. In the form of compounds with metals ( sulfides) it occurs in the form of ores on land and is part of deep-sea sediments. These compounds are converted into a soluble form available for absorption by organisms by so-called chemosynthetic bacteria, which are capable of obtaining energy by oxidizing reduced sulfur compounds. As a result, so-called sulfates that are used by plants. Deeply buried sulfates are involved in the cycle by another group of microorganisms that reduce sulfates to hydrogen sulfide.
Diagram of the phosphorus cycle.
Finally, it is necessary to consider the biogeochemical cycles of carbon and water. Carbon is of exceptional importance for living matter. Millions of organic compounds are created from carbon in an ecosystem. Carbon from atmospheric carbon dioxide is assimilated through the process of photosynthesis carried out by plants and converted into organic compounds of plants and then animals. At the next stage of the cycle, organic mass, as a result of respiration and decomposition, turns into carbon dioxide or settles in the form of organic deposits (for example, peat), which, in turn, give rise to many other compounds - coal, oil. A very small part of the total mass of carbon is involved in the active cycle of carbon dioxide in living matter. A huge amount of carbon dioxide is preserved in the form of fossil limestones and other rocks.
There is a fluid equilibrium between atmospheric carbon dioxide and ocean water. Organisms absorb calcium carbonate, create their skeletons, and then layers of limestone are formed from them. The atmosphere is replenished with carbon dioxide due to the processes of decomposition of organic substances, carbonates, etc. Particularly powerful sources are volcanoes, whose gases consist mainly of water vapor and carbon dioxide, and human combustion of fossil fuels.
During the water cycle, moisture evaporates from the surface of reservoirs and enters the air, after which it is transported by air currents over long distances. Subsequently, water is released from the atmosphere through precipitation. Some of them dissolve rocks and thus make the compounds contained in them available for absorption by producers. Due to precipitation, a groundwater fund is also formed. We should not forget about the consumption of water by living organisms. Particular attention should be paid to the fact that reservoirs lose more water through evaporation than they receive through precipitation. In addition, human activities are reducing groundwater recharge. Consequently, water is a difficult-to-renew resource that requires very rational use.
Diagram of the sulfur cycle.
Carbon cycle diagram.
Diagram of the water cycle.
Thus, the main property of substance flows in ecosystems is their cyclicity. Substances in ecosystems undergo a complex multi-stage cycle, first reaching living organisms, then into the abiotic environment and again returning to the organisms. At the same time, part of the mass of substances may fall out of biogeochemical cycles for a long time. Biogeochemical cycles of substances accompany energy flows in ecosystems. Human intervention in these processes can adversely affect the state of individual ecosystems and the biosphere as a whole.
The vital activity of a biogeocenosis is possible only under the condition of a constant flow of energy and the circulation of substances in it (biotic circulation). However, since in the life activity of biogeocenosis, along with living organisms great value have chemical and geological factors, the circulation of substances in a biogeocenosis should be considered from the perspective of the biogeochemical cycle, which is not identical to the biotic cycle, which implies the extraction by living organisms of large quantities of mineral substances from the surrounding inanimate nature and the return of their chemical elements to the environment after their death, i.e. e. circulation of substances between the hydrosphere, lithosphere, atmosphere and living organisms.
The cycle of substances is never completely closed in a circle, because part organic and inorganic substances is carried outside the biogeocenosis and at the same time their reserves can be replenished due to influx from outside. Incomplete closure of cycles on geological time scales leads to the accumulation of elements in various natural spheres of the Earth. In this way, minerals are accumulated - coal, oil, gas, limestone, etc.
The constant flow of energy into the ecosystem occurs due to solar radiation, which is converted by photosynthetic organisms into the energy of chemical bonds of organic compounds. The transfer of energy through food chains obeys the second law of thermodynamics: the transformation of one type of energy into another involves the loss of some energy. At the same time, its redistribution is subject to a strict pattern: the energy received by the ecosystem and assimilated by producers is dissipated or, together with their biomass, is irreversibly transferred to consumers of the first, second, etc. orders, and then to decomposers with a drop in energy flow at each trophic level. In this regard, there is no energy cycle.
We can talk about the cycle of substances only in a very narrow sense of the biotic cycle: the supply of biogenic elements (carbon, oxygen, nitrogen, etc.) to living organisms and the return of these same biogenic elements to the environment (i.e., the consumption and return of biogenic elements occurs according to circle).
In biogeocenosis, the circulation of substances occurs both between geospheres (atmosphere, hydrosphere, earth's crust, granite, basalt and other spheres) within 10-20 km (in some places 50-60 km) from the Earth's surface, and between some geospheres and living organisms. Directly continuous circulation of substances is observed in the atmosphere, hydrosphere, upper part of the solid lithosphere and in the biosphere. Human activity has now added to the geological force in this cycle.
Thus, two main cycles are distinguished:
- large (geological) - lasting millions of years, lies in the fact that rocks are subject to destruction, and weathering products (including water-soluble nutrients) are carried by water flows into the World Ocean, where they form marine strata and only partially return to land with precipitation. Geotectonic changes, processes of subsidence of continents and rise of the seabed, movement of seas and oceans over a long period of time lead to the fact that these strata return to land and the process begins again.
- small (biotic) - (part of a large one), occurs at the ecosystem level and consists in the fact that nutrients, water and carbon accumulate in the substance of plants, are spent on building the body and on the life processes of both these plants themselves and other organisms (both rule of animals) that eat these plants (consumers). The decay products of organic matter under the influence of decomposers and microorganisms (bacteria, fungi, worms) again decompose into mineral components that are accessible to plants and are drawn into the flow of matter by them.
which are collectively called the biogeochemical cycle. Almost all chemical elements are involved in such cycles, and primarily those that are involved in the construction of a living cell, for example, the human body, which consists of oxygen (62.8%), carbon (19.37%), hydrogen (9.31%). ), nitrogen (5.14%), calcium (1.38%), phosphorus (0.64%) and about 30 more elements.
The most intense biogeochemical cycle. In nature, carbon exists in two main forms - in carbonates (limestone, chalk, marble) and organic minerals(oil, coal, natural gas). All these substances have low chemical activity and therefore are used only to a very small extent by living organisms. Only those parts of carbon that are found in the atmosphere, hydrosphere, and living organisms participate in the biotic cycle.
IN atmospheric air carbon is contained in the form of carbon dioxide, which accounts for 0.03%. The latter is absorbed by plants and goes into the formation of organic matter during photosynthesis. Plants are eaten by herbivorous animals, in whose bodies carbon in organic compounds passes through a chain of metabolic reactions. Some of it accumulates in their body, some is removed with waste products. Carbon dioxide is released during the respiration of animals and plants. Dead plants and animals are exposed to decomposer microorganisms (bacteria, fungi), which, decomposing them, convert carbon-containing substances into carbon dioxide, which is returned to the atmosphere. At the same time, methane (CH 4), water and nitrogen compounds (NH 4, CO(NH 2) 2, NO 2, NO 3) are returned to the biotic cycle. Huge amounts of methane are released by methane bacteria that live in soil and swamps. In addition, carbon reserves in the atmosphere are replenished due to volcanic activity and human combustion of fossil fuels.
Most of the carbon dioxide entering the atmosphere is absorbed by the oceans and seas (since it is highly soluble in water)
CO 2 + H 2 0 --> H 2 CO 3 --> H + + HCO 3 -
and is deposited as water-insoluble calcium carbonate after the carbonate ion (HCO 3 -) combines with calcium
Ca 2+ + HCO 3 - --> Ca 2 CO 3 + H +
Calcium carbonate falls into the bottom sediments of water bodies. It is also absorbed by aquatic organisms and used by them to build shells (molluscs) or outer coverings of the body (crustaceans). Ordinary chalk is formed by the compacted remains of fossil mollusk shells. Thus, a share of excess CO 2 is absorbed by the World Ocean and removed from the biotic cycle. However, the ability of the World Ocean to absorb excess CO 2 is not unlimited and is currently believed to be close to exhaustion. Accordingly, the atmospheric part of CO 2 is slowly but steadily increasing. According to calculations, in 2025, 26 billion tons of carbon in the composition of carbon dioxide will be released into the Earth's atmosphere, which corresponds to an annual increase of 3.4%.
Oxygen cycle is closely interconnected with the carbon cycle since both elements are part of carbon dioxide and are the most important components of all organic compounds - carbohydrates, fats and proteins, nucleic acids, high-energy compounds.
In quantitative terms, the main component of living matter is oxygen, the circulation of which is complicated by its ability to enter into various chemical reactions, mainly oxidation reactions. As a result, many local cycles occur between the atmosphere, hydrosphere and lithosphere.
Oxygen contained in the atmosphere is of biogenic origin and is considered a product of photosynthesis, which maintains its content in the atmosphere at about 21% In addition, large number oxygen is found in the most common minerals earth's crust- sand rocks (SiO 2), iron (Fe 2 O 3) and aluminum (Al 2 O 3) ores, which, however, does not participate in the biotic cycle, because These substances have low chemical activity and are therefore used only to a very small extent by living organisms. The biotic cycle primarily involves only those parts of oxygen that, like carbon, are found in the atmosphere, hydrosphere, and living organisms.
Free oxygen is used for respiration by all aerobic microorganisms and is used for the oxidation of organic substances, resulting in the release of final product oxidation - carbon dioxide. As part of carbon dioxide, oxygen returns to the external environment and this cycle ensures the circulation of all biogenic elements, since the release of energy from organic and inorganic compounds accompanied by their splitting during oxidative reactions. In some respects, the oxygen cycle resembles the reverse carbon dioxide cycle.
Note that, starting from a certain concentration, oxygen is very toxic to cells and tissues (even in aerobic organisms). But a living anaerobic organism cannot withstand (this was proven in the last century by L. Pasteur) an oxygen concentration that exceeds the atmospheric one by 1%.
The consumption of atmospheric oxygen and its replacement by plants during the process of photosynthesis occurs quite quickly. Calculations show that it takes about two thousand years to completely renew all atmospheric oxygen. On the other hand, it takes two million years for all the water molecules in the hydrosphere to be photolyzed and re-synthesized by living organisms.
Part of the oxygen entering the atmosphere can be fixed by the lithosphere in the form of carbonates, sulfates, iron oxide, the rest circulates in the biosphere in the form of gases or sulfates dissolved in oceanic and continental waters.
Thus, the carbon and oxygen cycle are interconnected by the processes of photosynthesis and respiration: during photosynthesis, carbon dioxide is absorbed (fixed by organisms), and the carbon contained in it is used to form organic substances with the participation of water, light and photosynthetic pigments. The released oxygen is formed by the splitting of water, and the released carbon dioxide is formed due to respiration and decomposition of organic compounds.
The processes of photosynthesis on the one hand, respiration and decomposition of organic compounds on the other, mutually balance each other. Therefore, the amount of carbon and oxygen participating in the biotic cycle remains fairly constant. The involvement in this system of carbon formed as a result of geological processes (volcanic eruptions, fires and chemical interaction with various compounds) is insignificant, however, if the production and destruction of organic matter is disrupted, prerequisites are possible for the increased formation of organic minerals (bital coals, oil shale, etc.) .d.), and to slow down this process.
Anthropogenic factors (industrial development, burning of fossil fuels, wars, plowing of the soil during agriculture, reduction in forest area - tropical forests of the Amazonian lowland, Tropical Africa and Southeast Asia, which are the main producers of oxygen on the planet, etc.) can more clearly disrupt balance between these biotic elements. Over the past 100 years, albeit slightly, the oxygen content in the atmosphere has been decreasing. This does not pose a danger to the respiration of living organisms either now or in the distant future, but it does lead to a decrease in the ozone content in the upper layers of the atmosphere (" ozone holes"), which contributes to an increase in the flux of hard ultraviolet radiation reaching the Earth's surface.
An increase in CO 2 concentration in the atmosphere causes the greenhouse effect. It is due to the fact that CO 2 and other greenhouse gases, such as methane, prevent the heat flow emitted by the earth's surface heated by the sun's rays from going into outer space. This leads to a constant increase in the temperature of the above-ground layer of the atmosphere and, so far, to a very slow (up to 1-2 mm per year) rise in the level of the World Ocean, a significant reduction in the area of permanent ice in the Arctic Ocean, a retreat to the north of the edge of the Arctic ice and the southern borders of the tundra and forest-tundra zones .
On the other hand, an increase in the content of dust, smoke and other solid pollutants in the atmosphere can reduce the temperature of the surface layers of the atmosphere, since dust reflects the sun's rays into outer space, which reduces their heating of the earth's surface (mirror effect). Mathematical modeling consequences of a military conflict, even with limited use of nuclear weapons, showed that smoke and dust in the atmosphere can lead to a decrease in the average temperature on the Earth's surface by 5-6 ° C, which will cause the onset of a new ice age ("nuclear winter").
The future of humanity largely depends on which of the possible scenarios for the development of atmospheric processes ("global flood" or "ice age") can be realized as a result of human intervention.
Nitrogen is one of the main biogenic elements that is part of proteins. Living organisms contain an average of 3% nitrogen. On Earth, nitrogen reserves are enormous. In the atmosphere alone, its content by volume is 79%.
Gaseous nitrogen arises as a result of the oxidation reaction of ammonia formed during volcanic eruptions (this is juvenile nitrogen, which was not previously part of the biosphere) and the decomposition of biological waste. However, in a free state, it is not absorbed by either higher plants or animals. Molecular nitrogen has a very weak reactivity; it is not toxic, but does not support life processes. The very name “nitrogen” translated from ancient Greek means “lifeless” (a is a negative particle, “zoon” is life).
Eukaryotes can only use “fixed nitrogen”, which is part of inorganic and organic substances, such as ammonia (NH 4), nitrites (NO 2 - ) and nitrates (NO 3 - ), as well as proteins.
Free (molecular) nitrogen is converted into organic compounds by nitrogen-fixing bacteria and blue-green algae. In addition, a small part of free nitrogen under the influence of electrical discharges in the atmosphere can be converted in combination with water into nitrous and nitric acids. The latter, entering the soil, form salts. In a bound state, nitrogen (in the form of nitrate ions (NO 3 - ) and ammonium ions (NH 4 +)) is absorbed by plants [show] and is used for protein synthesis.
Its fertility greatly depends on the amount of fixed nitrogen in the soil. Even in Ancient Greece and Rome they knew that legumes (beans, peas) sharply increase soil fertility, while other crops reduce it. The founder of botany, Theophrastus, and the Roman scientists Cato, Varro, Pliny the Elder and Virgil wrote about this. However, only in 1830 the French agricultural chemist J.B. Boussingault discovered that legumes enriched the soil with nitrogen, but mistakenly believed that plants for some reason were able to fix molecular nitrogen from the atmosphere. In fact, legumes obtain nitrogen through symbiotic nitrogen fixation thanks to nodule bacteria, which was shown by M.S. Voronin in 1866 and confirmed by G. Gelriegel.
Nodule bacteria are special nitrogen-fixing bacteria on the root system of plants of the legume family. They got their name because of their ability to form special thickenings (nodules) on the roots. Nodule bacteria are the most active consumers of nitrogen, converting it into nitrates. Currently, about 13 thousand species of leguminous plants are known, on the roots of which nitrogen-fixing bacteria settle. In addition, the latter also settle on the roots of about 200 species of plants from other families, for example, alder, sea buckthorn, etc.
Among nitrogen-fixing bacteria there are also free-living species that live in soil, water, bottom silt, etc. Some species are even found in the rumen of ruminants.
Some actinomycetes and cyanobacteria also fix nitrogen. Therefore, the latter are able to live in bodies of water that contain almost no nutrients, for example, in geothermal springs. High rice yields in the countries of Southeast Asia are largely due to the fact that cyanobacteria intensively develop in flooded rice fields, enriching the bottom silt with bound nitrogen.
Nitrogen-fixing cyanobacteria form mutualistic associations with some moss species, such as sphagnum moss, Azolla aquatic fern, gymnosperms and flowering plants. Symbiont nitrogen fixation is estimated on average at 100-200 kg per ha per year, while its fixation by free-living organisms is only 1-5 kg per ha per year.
It is believed that the biological fixation of nitrogen in the biosphere is 150 million tons. By comparison, global production of nitrogen fertilizers in 2000 was 85 million tons.
The biological nitrogen fixation mechanism is controlled by a small group of compactly located 20 genes (nif system). Its structure is almost the same for different groups of nitrogen fixers (bacteria, cyanobacteria). Some viruses are able to tear off the nif system from the DNA molecule of a nitrogen-fixing bacterium and attach it to the DNA of other bacterial species. It is assumed that the nif system arose relatively recently in a single species of bacteria; it was then transferred by viruses to other types of bacteria and cyanobacteria.
Plants with nitrogen-fixing symbionts are often pioneer species that settle in nitrogen-poor soils in the early stages of succession. As a result of their activity, the content of fixed nitrogen in the soil can increase so much that it ceases to be a limiting factor for other plant species. Therefore, during the process of succession, such soils are quickly populated by other plant species, which then displace the pioneer species. Therefore, leguminous plants almost never dominate in climax communities. For the same reason, in agriculture It is impossible to grow legumes in the same field for several years in a row. Their crops are suppressed by weeds that grow intensively in nitrogen-enriched soils. Therefore, leguminous plants are sometimes called “suicide plants” or “kamikaze plants.”
Plant proteins are consumed by animals and humans as food. In their bodies, proteins are broken down into amino acids and urea, which is then released into the external environment. After the death of organisms, putrefactive (ammonifying) bacteria decompose nitrogen-containing compounds into ammonia, and chemosynthesizing (nitrifying) bacteria convert ammonia into nitrogen and nitrogen salts. nitric acids, which can again be absorbed by plants. These reactions release energy, which is used by nitrifiers to form ATP and synthesize organic compounds. Therefore, nitrification processes are sometimes called “nitrogen respiration.”
Denitrifying bacteria break down ammonia to free nitrogen. The result is a depletion of soil and water in nitrogen compounds and a replenishment of molecular nitrogen in the atmosphere. A certain amount of nitrogen compounds settles in deep-sea sediments and is excluded from the cycle for a long time (millions of years). These losses are compensated by the entry of nitrogen into the atmosphere with volcanic gases. This closes the nitrogen cycle.
The activities of nitrogen-fixing and denitrifying bacteria mutually balance each other. Therefore, the amount of atmospheric nitrogen fixed by nitrogen fixers is approximately equal to the amount returned by denitrifiers to the atmosphere, which makes it possible to maintain nitrogen reserves in the biosphere at a constant level. The cycle period of the entire supply of nitrogen in the biosphere is estimated at approximately 1000 years.
Human agricultural activity, aimed at obtaining high yields of agricultural crops, changes the balance of nitrogen in the biogeocenosis due to the introduction of nitrogen fertilizers into the soil. These can be either organic fertilizers - peat chips, rotted leaves, waste products of living organisms (guano - bird excrement), or mineral fertilizers (superphosphate, ammonium nitrate, etc.), the industrial production of which is constantly growing.
The widespread and, in some cases, incorrect use of mineral fertilizers (nitrogen, phosphorus, potassium) in agriculture leads to their leaching from the soil into water bodies by precipitation and groundwater. A particularly large amount of nitrogen compounds accumulates in stagnant bodies of water - ponds, low-flow lakes, as well as in wells that take water from the uppermost aquifer, increasing the maximum permissible concentration nitrogen in drinking water.
An increase in the content of nutrients in a reservoir leads to their eutrophication and intensive development of autotrophic organisms, primarily planktonic algae. A clear example of this is the bloom of reservoirs, which has such unpleasant consequences, such as a decrease in the recreational properties of water bodies, deterioration in water quality, and the death of many species of aquatic organisms, including fish. Therefore, in recent years Unconventional methods are being developed to increase the nitrogen content in the soil:
- The cultivation of a number of strains of nitrogen-fixing bacteria has been established at factories for protein and vitamin preparations. Their concentrated culture, combined with mineral fertilizers, is applied to the soil or added to livestock feed.
- Experiments are being done to introduce genes of nitrogen-fixing bacteria, which regulate nitrogen fixation, into other types of soil bacteria.
- Research is being carried out to develop strains of nitrogen-fixing bacteria that could develop on the roots of cultivated plants, for example, cereals, cruciferous plants and nightshades.
Quantitatively, water is the most common inorganic component of living matter. At three states of aggregation it is present in everyone components biosphere: atmosphere, hydrosphere and lithosphere. If water in various hydrogeological forms is evenly distributed over the corresponding regions of the globe, then layers of the following thickness are formed:
- for the World Ocean 2700 m,
- for glaciers 100 m,
- for groundwater 15 m,
- for superficial fresh water 0.4 m,
- for atmospheric moisture 0.03 m.
The water cycle is a closed cycle that can occur in the absence of life, but living organisms modify it.
Atmospheric moisture plays the main role in the circulation and biogeochemical cycle of water, despite the relatively small thickness of its layer. Under the influence of solar energy, water evaporates from the surface of reservoirs and is transported over long distances by air currents. Falling onto the land surface in the form of precipitation, it is spent on seepage (infiltration), evaporation and runoff.
Percolation is especially important for terrestrial ecosystems because it helps supply water to the soil and, by promoting the breakdown of rocks, makes their constituent minerals available to plants, microorganisms and animals. During the process of infiltration, water, eroding the upper soil layer, along with chemical compounds dissolved in it and suspended organic and inorganic particles, enters aquifers, underground rivers, seas and oceans.
Evaporation of water occurs in two ways: a significant amount of water is released by the plants themselves with their foliage after extracting it from the soil; the other part of the water evaporates from the soil surface. Evapotranspiration (trees and soil) play main role in the water cycle on continents.
Water flow is the process of rain, melt and groundwater flowing into reservoirs, occurring along the earth's surface (surface runoff) and in the thickness of the earth's crust (underground runoff). Runoff is also an integral part of the moisture cycle on Earth and consists of three phases: high water, floods, and low water. A special feature of runoff is its variability in space and time. There are channel and slope drainages. As vegetation density decreases, runoff becomes a major cause of soil erosion.
Water also participates in the biological cycle, being a source of oxygen, which enters the atmosphere, and hydrogen, which is fixed in the form of organic compounds. However, photolysis of water in plant cells during photosynthesis does not play a significant role in the cycling process. Also, the water consumed by animals, which is released into the external environment along with metabolic products, does not play a significant role.
| Content | |
| in organic nature | in an inorganic natural environment |
|
|
| Sulfur is an extremely active chemical element of the biosphere and migrates in different valence states depending on the redox conditions of the environment. | |
From natural sources, sulfur enters the atmosphere in the form of hydrogen sulfide, sulfur dioxide and particles of sulfate salts. Technogenic emissions of sulfur into the atmosphere (mainly in the form of oxides) occur during the combustion of fossil fuels. Reactions that lead to acid precipitation occur in the atmosphere:
2SO 2 + O 2 --> 2SO 3 ,
SO 3 + H 2 O --> 2H + + SO 4 2- .
With water runoff, sulfur enters the World Ocean and is absorbed by marine life. Especially a lot of sulfur accumulates in shellfish. The sulfur cycle in the seas occurs thanks to sulfate-reducing bacteria. Some of them accumulate sulfur in their bodies, and after the death of the bacterium, all the sulfur remains at the bottom of the ocean.
On continents, the sulfur cycle occurs thanks to plants. Chemosynthetic bacteria, capable of obtaining energy by oxidizing reduced sulfur compounds, convert sulfur into a form available for absorption by plants. Plants synthesize sulfur-containing amino acids - cysteine, cystine, methionine, which are supplied to food. When plants die, sulfur again passes into the soil, where bacteria reduce organic sulfur to mineral sulfur, and then again oxidize to sulfates, which are absorbed by plant roots. Deeply buried sulfates are involved in the cycle by another group of microorganisms that reduce sulfates to hydrogen sulfide (Fig. 77).
From the rocks of the earth's crust, inorganic phosphorus is partially washed out by sediments and enters river systems, seas and oceans, and is partially absorbed by plants, which, with its participation, synthesize various organic compounds and are thus included in trophic chains. Phosphorus moves through food chains from plants to all other organisms in the ecosystem. Organic phosphates are then returned to the ground along with excreta or corpses, where they are again exposed to microorganisms and converted into forms used by green plants. The circulation here takes place under natural optimal conditions with a minimum of losses.
In water sources, due to the constant sedimentation of organic substances, part of the phosphorus settles in deep-sea sediments and is turned off from the cycle until tectonic movements that can lift sedimentary rocks to the surface. The other part of phosphorus is included in the cycle, promotes the development of phytoplankton and living organisms and, thanks to fishing, is returned to land in small quantities.
In addition, human activities have a great influence on the phosphorus cycle. The extraction of large quantities of phosphate ores for mineral fertilizers leads to a decrease in the amount of phosphorus in one biogeocenosis and an increase in another. Runoff from fields, farms and municipal waste containing phosphorus from detergents, lead to an increase in phosphate ions in water bodies, to a sharp growth of aquatic plants and an imbalance in aquatic ecosystems.
Cycle of radioactive substances
Since 1944, man began to introduce radioactive substances into the biogeochemical cycle. The importance of some of them can be illustrated by the example of strontium-90. In the cycle of sediment formation and erosion, strontium moves along with calcium. Calcium makes up 7% of the material carried by rivers. Strontium enters the biological cycle system along with calcium. In the Far North, where large amounts of radioactive fallout fell, lichens absorb almost 100% of the radioactive particles falling to the ground. Reindeer that feed on lichens concentrate strontium in their bodies, and it then accumulates in the tissues of people who eat the meat of these animals; The body of some people already contains 1/3-1/2 of the permissible dose of strontium. This problem also exists in other areas. In Europe and North America, there has been a steady increase in strontium content in the bones of children and adults who received it in milk from cows, which in turn received it from plants. Accumulation radioactive isotopes in organisms is often used to determine the trophic relationships of organisms in communities.
Conclusion
Thus, biotic and geological cycles make it possible to maintain the existence of life on earth. At the same time, the intensity of vital activity of all three main components organic world- producers (manufacturers), consumers (consumers) and decomposers (destroyers) - are necessarily in mutual equilibrium and, experiencing the influence of factors of inanimate nature, change environmental conditions through their activities, i.e. their habitat. This leads to a change in the structure of the entire community - the biocenosis.
PEDAGOGICAL UNIVERSITY OF "THE FIRST SEPTEMBER"
CHERNOVA N.M.
Course “For biology teachers about the basics of ecology”
Course curriculum
Newspaper no. |
Educational material |
Lecture 1. Why should you study ecology? |
|
Lecture 2. Organism and environment |
|
Lecture 3. Ecological adaptations |
|
Lecture 4. Environment-forming role of organisms |
|
Lecture 5. Biocenoses |
|
Lecture 6. Populations |
|
Lecture 7. Ecosystems |
|
Lecture 8. Biosphere |
|
Final work. |
|
Lecture 7. Ecosystems
The condition for the existence of all living organisms is the flow of matter and energy. In their life activities, organisms use the energy of chemical bonds organic molecules, of which their bodies are composed. They either synthesize these molecules themselves from simple inorganic substances that are obtained from the environment, or transform them from compounds coming from the bodies of other organisms. Accordingly, all living beings are divided into autotrophic And heterotrophic . Autotrophs use either the energy of sunlight for synthesis ( phototrophs), or the energy of chemical bonds of inorganic substances ( chemotrophs). Heterotrophs are energetically dependent on other organisms, because able to transform only organic compounds.
Already from this simple diagram given in school textbooks, the close material-energy dependence of organisms on each other is obvious. The vast majority of species in nature are heterotrophs. This is a significant part of bacteria, protozoa, all fungi and animals. They exist, ultimately, at the expense of autotrophic organisms, which include all plants, some bacteria and some protozoa. However, photosynthetic organisms, being independent from others in terms of energy sources, need the assistance of heterotrophs in providing themselves with substances. They can use only a limited range of inorganic compounds (for example, carbon - in the composition of carbon dioxide; nitrogen, phosphorus, potassium - only in the composition of certain salts, etc.). These compounds involved in the process of organic synthesis are called nutrients, or nutrients. Their supply in the environment is always limited. This is easy to see from the example of a rapid drop in crop yields if plant products are taken out of the fields and no fertilizers are applied to the soil. Nutrients enter the environment due to the activity of heterotrophs, decomposing plant residues and other dead organic matter. The respiration of all living creatures returns carbon dioxide necessary for phototrophs to the atmosphere.
This mutual material-energy dependence connects species in biocenoses with each other and the surrounding inanimate nature, from where nutrients and energy come and where metabolic products are removed. In biocenoses, a cycle of nutrients arises and is maintained, called biological cycle . Life on Earth has existed for billions of years without depleting the necessary elements. According to Academician V.R. Williams, the only way to make a finite quantity infinite is to make it rotate along a closed curve. This method was found by nature at the dawn of the development of life, and it is the biological cycle that is the main reason for the preservation of life on the planet.
Any cells of nature in which the biological cycle of matter occurs are called ecosystems. The structure of any ecosystem must contain four components necessary for the implementation of the biological cycle: biogenic elements in the environment and three groups of organisms with different functions: producers, consumers and decomposers. Producers create biological products - organic substances from biogenic elements, consumers convert them into organic compounds own bodies, A decomposers again decompose these compounds into molecules digestible by producers.
In the majority natural ecosystems The function of producers is performed by green plants, consumers are animals, and decomposers are fungi and bacteria. However, strictly speaking, any organism is partially inherent in the function of a decomposer, since both animals and plants excrete part of their metabolic products in the form of simple inorganic molecules - carbon dioxide, ammonia, salts, etc. In the same way, both fungi and heterotrophic bacteria use part of the consumed organic matter to build their bodies, i.e. act as consumers. Therefore, appropriate names are given to certain groups of organisms according to the predominant role they play in ecosystems.
In nature, one can distinguish ecosystems of very different scales, with varying degrees of isolation and intensity of the biological cycle, different durations of existence - from temporary, ephemeral, to permanent and stable. For example, a drying puddle can function as a temporary ecosystem, in which unicellular algae, small filter feeders - rotifers, daphnia crustaceans and, of course, bacteria have developed. A decaying stump, overgrown with moss and lichen and inhabited by fungi, bacteria and invertebrate animals, is also a small, temporary ecosystem. A pond, lake, sea and ocean can be considered as ecosystems of successively increasing degrees of complexity, with at different times existence in the biosphere. Small ecosystems are part of larger ones, and together they represent components of the global ecosystem of the Earth - biosphere .
The completeness of the cycle of substances in ecosystems can be very different. Being largely dependent on the ratio and characteristics of producers, consumers and decomposers, it also depends on factors external to the ecosystem, for example, climate change, weather or anthropogenic impact. In a drying puddle, atoms of carbon, nitrogen and other biogenic elements can complete several cycles, moving from the bodies of organisms to the external environment and back, but most of them then leave this cycle, entering the soil or air and moving into other cycles. Ecosystems such as mature oak forests or feather grass steppes can maintain the cycling of their elements for a long time, returning to plants the substances necessary for photosynthesis and exist for thousands of years if external forces do not disrupt their composition and structure. But even in the largest and most stable ecosystems, the biological cycle is not completely closed. Part of the substance can fall out of it for a long time, settling on the ocean floor, in soils, swamps, etc., while the other part escapes to other ecosystems, carried by water, wind, and living organisms. As a result, all ecosystems of the planet are interconnected.
In some types of ecosystems - flowing - stability is maintained not so much by the cycle of nutrients, but by the balance of the supply and removal of substances. Rivers are a typical example of such ecosystems.
The continuity and unity of living and inanimate nature has long been recognized by researchers. Many terms have been proposed to designate individual areas of the environment where this unity is most clearly manifested (for example, microcosm– for the lake, etc.). Term ecosystem was proposed in 1935 by the English botanist A. Tansley and established itself as a universal concept applicable to natural formations of various ranks, in which the exchange of substances and energy is maintained between the abiotic environment and the community of organisms inhabiting it. Almost simultaneously, Russian geobotanist V.N. Sukachev proposed the term biogeocenosis to denote a similar system that occurs within a phytocenosis, i.e. units of vegetation cover. Both terms have taken root in science and are used in a similar sense with minor differences. Not every ecosystem can be called a biogeocenosis - the boundaries of the latter are determined in nature by phytocenosis, i.e. a certain plant association (for example, spruce-sorrel forest, spruce-green moss forest, pine-white moss forest, mixed-grass meadow, sphagnum bog, etc.). The term ecosystem applicable not only to natural cells of different scales, but also to man-made ones: aquariums, greenhouses, fields, ponds, cabins spaceships etc., if they contain the necessary components that ensure at least temporary, partial biological circulation of substances.
Ecosystem research began to develop fully only in the 1950s, after methods for accounting for the flow of matter and energy in biocenoses were developed.
Any circulation of matter requires energy. The main mechanism for the implementation of the biological cycle is the food connections of organisms. The transfer of energy when one organism feeds another is subject to certain laws. If, for example, a herbivorous animal (goat, rabbit, locust, horse, etc.) ate an entire plant, the energy value of which we take as 100%, then part of this energy will return to the external environment as part of undigested tissue excreted in excrement. The main share of energy absorbed by an animal organism is used to maintain the functioning of cells, the vital activity of the organism as a whole, and is gradually converted into heat, which is dissipated in the surrounding space. (According to the second law of thermodynamics, any transformation of energy from one state to another is accompanied by the transition of part of it to heat, and all chemical reactions in cells obey this law). Another, smaller, portion of the energy absorbed from food can be stored in the body in a chemically bound form as part of the body’s weight gain.
According to average data, the portion of the plant’s energy “retained” in the body of the animal that ate it does not exceed 10%. A predator that has eaten a herbivore, under the same conditions, will retain in its body, respectively, no more than 1% of the energy originally contained in the plant. Thus, solar energy bound by the plant during photosynthesis is almost completely returned to the environment in the form of heat through two links of trophic links.
A specific sequence of organisms feeding on each other, in which the fate of the initial portion of energy can still be discerned, is called trophic chain , or power circuit . Although food connections in biocenoses are diverse and the general trophic network connecting species living together consists of many intertwining trophic chains, each of these chains includes only a few links. Food chains cannot be long, since the energy supplied to them quickly runs out. It can be traced in only four, maximum six, links. Energy cannot be transferred indefinitely and cannot circulate in an ecosystem in a circle, like nutrients. She must do it all over again. Life in general exists on the flow of energy. A figurative expression of the functioning of an ecosystem can be the wheel of a water mill: constant rotation (cycle of matter) in streams of water constantly coming from outside (energy flow).
The place occupied by an organism in the food chain is called trophic level . Food chains always begin with autotrophic organisms (in the vast majority of cases, plants) that create organic matter. They represent the first trophic level. On the second there are herbivorous organisms, on the third and further there are carnivores. Predators and species with a mixed type of diet can occupy different levels in different trophic chains. The sparrow that pecked the grain represents the second link in the food chain, and the sparrow that ate the insect represents the third or fourth, depending on whether the insect was herbivorous or predatory.
So, on average, only 10% of the energy received at the previous one transfers from one trophic level to another. This pattern, called in ecology ten percent rule, is extremely important for understanding how ecosystems function and for competent environmental management. It underlies the creation of secondary biological products in nature.
Biological products They call the amount of organic matter that is created per unit of time at a certain trophic level. There are primary and secondary biological products. The primary one is created by plants from inorganic components. Gross primary production is determined by the rate of photosynthesis, which depends on both the plant species and environmental conditions. Plants spend a significant part of gross primary production (on average 50–60%) on maintaining their own vital functions, and the rest goes to growth - increasing mass. This part contained in the created biomass is called pure primary production. Due to pure primary production, all heterotrophic organisms of the biocenosis ultimately exist.
Secondary biological products is an organic substance created by heterotrophs, i.e. processors. It arises from primary pure production and, according to the rule of energy transfer through food chains, is no more than 10% of plant energy. Thus, in nature, 10 times more solar energy is spent to create 1 kg of mass of a herbivore than to create 1 kg of plant mass, and at least 100 times more for 1 kg of predator mass.
On the planet - in the depths of the ocean, in places where hot mineral springs emerge and in some other conditions - ecosystems have been preserved where primary biological production is created not by photosynthetic organisms, but by chemosynthetic bacteria. However, in these communities, food chains develop according to similar ecological rules, with large energy losses during the transition from one link to another.
In agriculture, the laws of energy transfer through food chains are expressed in the well-known fact that it is much cheaper to grow 1 kg of wheat than to produce 1 kg of beef or pork. For the same reason, predatory animals are not bred for meat, and among domesticated herbivores, those that most efficiently process food for their own growth are used for this purpose: chickens, turkeys, ducks, pigs, large and small cattle, etc. As already said, 10% is an average value, and specific living organisms can be characterized by different values of this indicator. Among farm animals, for example, in pigs, the efficiency of using 1 kg of feed per 1 kg of live weight gain can reach 20% or more. For other species, despite the efforts of breeders, such results cannot be achieved. Pheasants and peacocks are bred almost exclusively for decorative purposes, since the proportion of energy used for growth is only 2–3%.
The “ten percent rule” defines the so-called pyramid of biological production in ecosystems. A tenfold decrease in the amount of organic matter created per unit of time across trophic levels can be schematically depicted in the form of steps of a pyramid of the appropriate scale. It is also called the energy pyramid because the output is equivalent to the energy contained in it.
Such a pyramid often does not work out if one evaluates not production, but biomass or the number of organisms at different trophic levels. Product, we recall, is the amount of organic matter that is created per unit of time, while biomass is an indicator reflecting the amount available on at the moment. This could be, for example, the total mass of all plants per hectare of forest, the mass of stem wood, the total weight of a herd of elk in a given forest, or the total weight of all animals in the ecosystem being studied. Term biomass applicable to a single organism - a tree, an elk, a person.
With high productivity, the total biological production of biomass of organisms of a certain trophic level can be very low if these organisms are quickly eaten by representatives of the next level. For example, single-celled algae in the ocean reproduce in favorable conditions at high speed, i.e. They are highly productive, but at any given moment they are always small in weight, because they are eaten away at no less speed by zooplankton and various filter feeders. Animals of the second and third trophic levels increase their mass tens of times slower, but the total weight of fish and bottom animals is higher than phytoplankton, since predators eat them at a slower rate. The pyramid of biomass in the ocean turns out to be upside down. Thus, the configuration of biomass pyramids in ecosystems is determined not by the ratio of energy transfer through food chains, but by how quickly or slowly the created products move to the next trophic level.
The productivity of land and ocean ecosystems is the basis for human life support. People need both plant and animal food, since the human body does not produce a number of essential amino acids, which he should receive mainly from animal proteins. Not only agricultural crops are used for the needs of human society, but also all those primary biological products that support animal husbandry and commercial species of marine and terrestrial animals. In addition to meeting human nutritional needs, primary biological products (for example, in the form of wood, etc.) are used in many industries, construction, transport, energy, and medicine. In conditions of a population explosion and rapid growth in the number of people on Earth, it is very important to assess the real capacity of the environment for the population of the entire planet and its individual territories. Therefore, after methods for assessing biological products were developed, the first task was to assess its scale in different parts land and ocean and on the planet as a whole.
Since the late 1960s. scientists different countries for 10 years they worked under the general International Biological Program (IBP), assessing gross and net biological production in various types of ecosystems. As a result of this gigantic work, a map of the productivity of the globe was created. Refinement and addition of the obtained data continues to this day.
IN the most productive In Earth's ecosystems, an average of no more than 25 g of organic matter is synthesized per 1 m2 per day (in terms of the dry weight of gross production). Such highly productive ecosystems include tropical rainforests, river estuaries in arid regions, and coral reefs in tropical seas. Optimal conditions for photosynthesis are created here: a lot of heat, light, water, and enough nutrients. Interestingly, the main primary production on coral reefs is produced by symbiotic unicellular algae - zooxanthellae, living in the bodies of corals and other invertebrate animals in illuminated layers of water.
In his fields, a person can also achieve such a high yield of production of some agricultural plants, but provided that all limiting factors are removed, i.e. provided that there is a sufficient amount of regularly applied fertilizers, irrigation, soil loosening, and protection from pests. This is the so-called intensive farming, which is very expensive and often does not pay off in increased yields.
Under conditions of a sharp lack of any one or more factors affecting photosynthesis, ecosystems with low biological productivity. These include cold and hot deserts, tundras, saline soils, as well as central ocean areas, even in tropical climates. In the tundras and polar deserts there is a sharp lack of heat, and the polar night lasts a long time. In hot deserts, the limiting factor is primarily a lack of moisture, and in the central parts of the oceans, with an excess of heat, light and water, there is a lack of nutrients, mainly nitrogen and phosphorus. The main quantities of them are carried into the ocean from the continents and are intercepted by algae of the regional seas. The daily primary production of such ecosystems does not exceed 1 g of dry matter per 1 m2.
Most of the Earth's ecosystems are average productivity, supplying from 1 to 5 g/m2 of dry matter per day. These are areas of the northern taiga, mountain forests, meadows, deep lakes, shallow seas, arable lands, etc. In steppes, savannas, small lakes illuminated to the bottom, daily production can reach 10 g/m2 or more.
The created organic matter enters the food chain as part of either living plants or their dead parts. In the first case, the power circuits are called pasture, in the second – detrital. In different types of ecosystems, energy flows through grazing and detrital chains are different. In forests, normally all herbivorous species (insects, rodents, ungulates, etc.) use about 10% of the annual growth of plants, the rest falls into litter, forming the forest litter. Thousands of different species of organisms - bacteria, fungi, animals - work to destroy it in detrital food chains. In steppes and meadows, pasture chains can supply 50–70% of annual plant production; detritus chains are less developed here. Algae production is most intensively consumed in the oceans.
Dead, undecomposed, organic matter in ecosystems is called mortmass. Organisms that destroy mortmass belong to the destruction block of ecosystems. Slowing down their activity leads to the accumulation of dead organic matter on the soil surface (steppe rags, forest litter) or its burial (swamp peat, sapropel at the bottom of lakes, etc.).
Mortmass reserves indicate the rate of matter turnover in ecosystems different types. In forests, a clear indicator is the ratio of the mass of litter to the mass of annual litter. In tropical forests, the total biomass of vegetation is more than 5000 c/ha, more than 250 c/ha of leaves and branches fall annually, but no more than 25 c/ha of litter is present, i.e. its ratio to litter is 0.1, since it is very quickly destroyed by consumers (bacteria, fungi, ants, termites, etc.). In the oak forests of the middle zone, with an annual litter of 65 kg/ha, the ratio of litter mass to this value is about 4. Consequently, only by the end of the fourth year will the supply of nutrients that the plants used during the year be fully returned. For the spruce forests of the northern taiga, the delay in the decomposition of the annual portion of litter is already 15–17 years. In such forests, there is a thick layer of coniferous litter on the ground, and the cycle of matter is greatly slowed down. It is even more slowed down in swamp ecosystems, where thick layers of peat gradually accumulate. In the steppes the circulation is intense and the corresponding index approaches unity, and in savannas it is approximately 0.2.
Tilling the soil, sowing, caring for agricultural plants, and controlling weeds and pests require labor and, accordingly, energy consumption. As a result, agroecosystems, unlike natural ones, receive, in addition to solar energy, additional energy from humans. Without this energy investment they cannot exist. Each abandoned field is quickly transformed into a natural ecosystem.
One of the main difficulties in maintaining agroecosystems is maintaining the balance of the biological cycle of matter. Removed from fields large masses crops containing nutrients. If equal amounts of these elements are not returned to the soil in the form of mineral or organic fertilizers, field productivity will quickly decline.
Detailed studies reveal the high complexity of even an extremely simple agrocenosis. By trying to preserve the harvest, we break many food chains and imbalance the community. Essentially, all efforts to create high-purity products for the benefit of humans are a “struggle against nature,” which requires a lot of labor, money and knowledge. In modern agricultural science, the most progressive direction is greening of production, that is, the use of such methods and techniques that would contradict natural laws as little as possible. Excessive chemicalization of soils, the use of potent pesticides, and heavy equipment are the main obstacles to achieving environmentally conscious farming.
Natural ecosystems are subject to processes of self-development. They change their species composition, structure and appearance until a stable balance of energy intake and expenditure is established in them. This natural, directed process of changing ecosystems as a result of the interaction of organisms with each other and with the abiotic environment is called succession . There are primary and secondary successions.
Primary successions lead to the formation of stable communities in initially lifeless areas. Such areas constantly appear on modern land as a result of local events: talus in the mountains, retreat of glaciers, destruction of rocks, formation of sand deposits, retreat of the water line on the coasts, etc. Succession was first analyzed using vegetation as an example by the American botanist F. Clements at the beginning of the last century. He identified a number of stages in the succession process. First, a bare area appears that is not yet inhabited by any organisms. Then its settlement begins: representatives of different types plants from surrounding biotopes in the form of seeds, fruits, spores or other rudiments. At the next stage, there is a strict selection of species under abiotic conditions, since not all are able to take root in this extreme environment. Then the established species begin to change the environment with their life activity: plants are removed from the soil mineral compounds, include them in their bodies, leave litter, dead roots, change the moisture capacity of the substrate, affecting the microclimate. After this, having completely mastered and changed the habitat, plants begin to compete with each other, and selection occurs mainly due to biotic factors. The composition of the community is transformed, new species are introduced into it, more competitive in a changing environment. Naturally, changes in the composition of vegetation are accompanied by changes in the animal, fungal, and bacterial worlds. This process continues until such a composition of the community is selected in which changes in the environment caused by the activities of some species are compensated by others and the entire biocenosis becomes capable of maintaining a balanced circulation of matter. Such an ecosystem becomes stable and exists until climatic conditions change or other external forces throw it out of balance. Final sustainable stage succession Clements called menopause, or menopause, initial stages – pioneers, and the whole series of changing communities leading to menopause - successional series. A clear example of primary succession is the overgrowing of stagnant bodies of water, when wetlands gradually appear in their place, then grasses and shrubs develop, giving way to forest vegetation.
The main pattern of the succession process is a gradual slowdown in the transformation of ecosystems. The first stages of a succession series are the most fleeting and unstable. The closer to the climax community, the slower changes in the environment and species composition occur. Dumps created as a result of construction activities or mining are overgrown before human eyes. In the beginning, communities change very quickly. Coltsfoot appears on bare dumps, and weeds appear in the second or third year. After a few years, they are replaced by cereal vegetation, then by shrubs, and the forest gradually grows.
Primary succession is a fairly long process, since it is accompanied by soil formation. Climax communities arise only at the stage when a soil profile corresponding to a certain climate and underlying rock is formed. On different substrates, the pioneer stages of successional series vary greatly. For example, fouling of bare rocks usually begins with crustose lichens; colonization of loose sands - with sedges and grasses that are resistant to wind exposure of the root system; overgrowing of small reservoirs - with lush aquatic and coastal vegetation: egg capsules, pondweed, duckweed, cattails, etc. Gradually, more and more people are being introduced into communities common types, and at the menopause stage they become similar to each other. There are few truly stable communities in nature that reproduce themselves and do not change for centuries. They form typical ecosystems characteristic of climatic zones and mountain zones. These are, for example, spruce forests of the middle taiga, oak forests of the broad-leaved belt, feather grass-fescue steppes, moss-shrub tundra, etc.
In addition to primary successions, which form stable ecosystems in areas of the environment that were initially unaltered by life, many secondary, or restorative, successions occur in nature. These are those changes in communities that begin after partial disruption of already formed ecosystems - for example, after a forest or steppe fire, forest cutting, or plowing virgin soil. In such cases, ecosystems often retain soil, seeds or plant roots, and some animal species survive. The community is again beginning to develop towards a sustainable, climax. In geobotany such changes are called demutations. For example, in the middle taiga, in burnt areas and clearings, thickets of fireweed and raspberries develop, then small-leaved tree species, and only under their cover the spruce forest gradually grows and replaces them. The stages and sequence of this process may differ from primary succession: for example, the restoration of spruce species may be preceded not by birch forests, but by aspen forests. Regenerative successions proceed faster than primary successions.
Succession is observed in communities of different scales and in areas of different sizes. Overgrown, going through natural stages, are tree falls in forests, gopher beds in the steppes, mole outcrops, the bottom of dried puddles, etc. In these areas, along with the plants, their entire population changes. Such small-scale successions constantly occur in all large ecosystems, restoring local disturbances. In all cases when primary production in a system is not equal to its consumption, the succession process begins, conditions change and species change.
Ecological successions are mechanisms for the development, self-maintenance and restoration of natural ecosystems. Knowledge of their laws is extremely important for rational environmental management. On the one hand, successions restore anthropogenic disturbances in natural ecosystems. The restoration of forests, mixed-grass steppes, and the overgrowing of dumps, screes, and ravines can be accelerated if these processes are properly stimulated. In the south of our country, technologies have been developed that make it possible to transform a degraded steppe into a highly productive multi-species steppe in a matter of years. Succession can be limited by a lack of water, seeds, and the saturation of the environment with toxic compounds. In all cases, to speed up the restoration of soils and vegetation, it is necessary to understand the nature of the limiting factors.
On the other hand, in order to obtain harvests, a person has to fight against natural successions. From environmental laws it follows that an ecosystem cannot be both stable and accumulate an excess of primary production. All our agroecosystems - fields, vegetable gardens, orchards - are extremely unstable pioneer communities; they require constant human support, otherwise they quickly become involved in the natural process of ecological succession. People pay for agricultural harvests with environmental instability.
The competent organization of the landscape is a mosaic of diverse ecosystems, both sustainable and pioneer, designed to obtain an excess of clean products. Fields from horizon to horizon are anti-ecological; they must alternate with shelterbelts, forests, copses, ponds, pastures, meadows, etc. It is also impossible, in accordance with the old optimistic slogan, to turn the entire earth into a blooming garden; this is also anti-ecological. The garden is also a pioneering and unstable ecosystem, to maintain which you will also have to fight “against nature.” A person must maintain around him all the diversity of ecosystems on which the sustainability of the natural environment is built.
Questions and tasks for independent work
1. How do the concepts of biocenosis, ecosystem and biogeocenosis relate to each other?
2. Why can’t there be an energy cycle in ecosystems?
3. What are primary and secondary biological products?
4. How do agroecosystems differ from natural ecosystems and how are they similar to them?
5. What is ecological succession and what are its stages?
Literature
Chernova N.M., Bylova A.M. General ecology. – M.: Bustard, 1998–2005.
Odum Yu. Ecology. T.1–2. – M.: Mir. 1986.
Miller T. Life in the environment. T.1. – M.: Pangea, 1993.
Nebel B. Environmental Science. T.1. – M.: Mir, 1993.
All living organisms in the process of life are in constant and active interaction With environment. The essence of this interaction is the exchange of matter and energy. The vital activity of an ecosystem and the circulation of substances in it are possible only under the condition of a constant flow of energy. The main source of energy on Earth is solar radiation. The energy of the Sun is converted by photosynthetic organisms into the energy of chemical bonds of organic compounds. The transfer of energy through food chains obeys the second law of thermodynamics: the transformation of one type of energy into another occurs through the loss of part of the energy. At the same time, its redistribution is subject to a strict pattern: the energy received by the ecosystem and assimilated by producers is dissipated or, together with their biomass, is irreversibly transferred to consumers of the first, second and other orders, and then to decomposers with a decrease in the energy flow at each trophic level. In this regard, there is no energy cycle.
Unlike energy, which is used only once in an ecosystem, substances are used repeatedly due to the fact that their consumption and transformation occurs in a circle. This cycle is carried out by living organisms of the ecosystem (producers, consumers, decomposers) and is called the biological cycle of substances. Under biological cycle refers to the flow of chemical elements from the soil and atmosphere into living organisms, in which the incoming elements are converted into new complex compounds, and their return to the soil and atmosphere in the process of life.
Ecological systems of land and the World Ocean bind and redistribute solar energy, atmospheric carbon, moisture, oxygen, hydrogen, phosphorus, nitrogen, sulfur, calcium and other elements. The vital activity of plant organisms (producers) and their interactions with animals (consumers), microorganisms (decomposers) and inanimate nature provides a mechanism for the accumulation and redistribution of solar energy entering the Earth.
The most important aspect of the existence of life on Earth are cycles (biogeochemical cycles), which involve water and the main biogenic chemical elements - C, H, O, N, P, S, Fe, Mg, Mo, Mn, Cu, Zn, Ca, Na , K, etc. All cycles consist of two phases: organic(during which a substance or element is part of living organisms) and inorganic. Successive transitions of a substance from one phase to another occur countless times. So, for example, annually passes through the organic phase and returns to the inorganic 1/7 of all carbon dioxide and 1/4500 of the oxygen in the atmosphere; It is estimated that all water turns over in 2 million years.
As an example, consider the nitrogen cycle, one of the most important chemical elements of living organisms. Nitrogen is building material for proteins, nucleic acids, ATP components, chlorophyll, hemoglobin, etc.
Nitrogen is distributed extremely unevenly in the biosphere. The soil contains only 0.02 to 0.5% of it, and this is only due to the activity of microorganisms, some plants and the decomposition of organic matter. At the same time, millions of tons of nitrogen in the atmosphere are literally pressing on the Earth's surface. Figuratively speaking, up to 80 thousand tons of this element “hang” over each hectare of soil. Despite the fact that there is a lot of nitrogen in the atmosphere (78%), most plants are not able to assimilate it in a molecular state. Nitrogen becomes an “element of life” only in chemical compounds—easily soluble nitrate and ammonia salts. However, there is no nitrogen bound (at least into simple oxides) in the air.
The exception is the release of nitrogen into the atmosphere as a result of emissions from motor vehicles, thermal power plants, boiler houses, and industrial enterprises. When fossil fuels (oil, coal, gas) are burned into the Earth's atmosphere, nitrogen oxides (N 2 0, N0 2) are released, which pollute the environment.
Only a few prokaryotic (prenuclear) organisms—some types of bacteria and cyanobacteria—can directly use atmospheric nitrogen. Higher plants can use nitrogen only as a result of symbiotic relationships with nitrogen-fixing prokaryotic organisms - nodule bacteria, which settle in the tissues of the roots of plants from the legume family, such as peanuts, soybeans, lentils, beans, alfalfa, clover, lupine, etc. By fixing atmospheric nitrogen, they supply the host plant with nitrogen compounds available to it in the form of nitrates and nitrites.
Dead nitrogen-containing organic matter (proteins, nucleic acids, urea) are decomposed by ammonifying bacteria to ammonia. It dissolves easily in water. Some of it can be absorbed directly by plants, some is washed out of the soil, and the remaining ammonia is exposed to the action of specialized bacteria as a result of the process nitrification - oxidation of nitrogen-containing compounds. Plant roots receive nitrites and nitrates formed during the reaction
NH 4 + -> N0 2 - -> N0 3 -
In nature, the reverse process is also carried out - the reduction of nitrites and nitrates to gaseous nitrogenous products - denitrification, As a result of this process, denitrifying bacteria reduce the NO3 - ion to N 2. Denitrification occurs in several stages:
N0 3 - -> N0 2 -> - N 2 0 -> N2
Thus, denitrification removes fixed nitrogen from soil and water and returns it to the atmosphere as nitrogen gas. Denitrification closes the nitrogen cycle and prevents the accumulation of nitrogen oxides, which are toxic in high concentrations.
The cycle of substances is never completely closed. Some organic and inorganic substances are carried outside the ecosystem, and at the same time, their reserves can be replenished due to influx from outside. In some cases, the degree of repeated reproduction of some cycles of the circulation of substances reaches 90-98%. Incomplete closure of cycles on geological time scales leads to the accumulation of elements in various natural spheres of the Earth. This is how minerals accumulate - coal, oil, gas, limestone, etc.
