The concept of soil biota. Soil biota is the biological world of the soil. Distribution of animals in the soil
soil biota - soil biological world
What is soil biota? Who is the most important?
If you ask a gardener, which of the living things in the soil are most beneficial to plants? What makes the soil fertile? Which living being maximizes fertility? Most will answer, of course, earthworms. Is it so? Who else is working for our harvest?
I in previous articles, from different angles, highlighted the role of microorganisms invisible to our eyes. Not just saprophytes that decompose soil organics and minerals, but nitrogen fixers that live in the rhizosphere, and which the plant attracts with its top dressing and which provide it with deficient nitrogen from the air. As well as fungi - symbionts that make scarce phosphorus available to plants.
Let's leave the rhizosphere. Let's talk about everything else. Let's imagine that leaves have fallen on the soil, or a cow has passed in a meadow and left a "flat cake". The transformation of organic material in the soil is carried out by successive living organisms. At first, literally in a matter of days, the sugar microflora will consume sugar, then, with a slight lag, the amino acid microflora will absorb the energy of the protein. Then they will be replaced by hundreds of species of living beings that destroy cellulose, this process reaches a peak in a month, and subsides by the end of the year. And the microorganisms that destroy lignin will work for several years. And, in the end, humus will accumulate in the soil, the structure and fertility of the soil will improve if the gardener does not greatly interfere with this.
So, the number of bacteria in the soil reaches colossal proportions (from 1 to 10 billion cells per 1 g of soil, and in the root zone, in the rhizosphere, 100 times more). It never remains constant during the growing season, as it depends on the input of organic matter, soil properties, its moisture content and temperature. Therefore, even within one month, from 6 to 10 peaks of maximum abundance, followed by a 3-fold decrease, can be recorded in the soil. The bulk of bacteria is concentrated in the upper layers rich in organic matter. The total biomass of bacteria in the soil is approximately from 1 to 5-7 t/ha. Bacteria die, are born, species change, and all this hundreds of times per season, and this is the “best food” for our plants.
The second place in importance should be given to mushrooms. It is they who are the first to begin to destroy coarse organic matter, high molecular weight carbohydrates, inaccessible to plants. In 1 g of soil of different types, from 10 to 300 thousand fungi are found. Their preferred habitat is limited to the surface layer of soil. The total length of fungal mycelium in soils of cold and temperate climates is measured from several hundred to thousands of meters per 1 g of soil. The maximum biomass of fungi (mycelia + spores) was noted in soddy-podzolic soils and is more than 200 g/m2. In some soils, the fungal biomass is estimated at 100-1000 kg/ha. This is about 5 times less than bacteria, but much more, for example, than the biomass of earthworms.
Few people know that after fungi, algae are not far behind in terms of their effect on soil fertility. If bacteria and fungi destroy organic matter, then algae, like higher plants, are producers of organic matter. Currently, about 2000 species of algae are known to occur in different types of soils. The largest amount of algae is concentrated in the upper soil horizon, limited by the depth of penetration of sunlight. Usually 1 g of soil contains from 5 thousand to 1.5 million cells. But under favorable conditions, the number of algae per 1 cm2 of the soil surface can reach 40 million, and the biomass can reach 1.5 and even 2 t/ha. During mass reproduction, algae colonies become clearly visible, as they give the soil a green tint or form a green crust several millimeters thick on it. Plants actively attract algae to their rhizosphere, as they accumulate nitrogen from the air and alkalize the soil, reducing acidity. And most importantly, they stick soil particles together with their mucus and threads, quickly improving its structure.
Briefly, about soil animals. The smallest and most numerous- these are microscopic unicellular: flagellates, rhizomes, amoeba and ciliates. All of them live in soil pores and capillaries filled with water, but unlike organisms living in water bodies, soil animals are able to remain viable for a long time with a lack of water and low temperatures. About 600 species of protozoa have been found in the soils of Russia. In the arable land of the Moscow region, 38 species of flagellates, 27 species of naked amoebas, 54 species of testate amoebas and 26 species of ciliates were found. In one gram of soil there can be up to 15 thousand shell rhizomes and up to 200 thousand flagellates, the live weight of flagellates was 50, and ciliates- over 200 kg/ha. The total biomass of protozoa reaches 300-400 kg/ha.
Microfauna also includes small multicellular organisms (rotifers, tardigrades, nematodes, mites and springtails). These organisms live in water films or in soil pores filled with moist air. The most numerous and superior in biomass are nematodes. In the soil, there are from 1 to 2.5 million individuals per 1 m2. The total biomass of springtails and mites is small and amounts to 10-20 kg/ha. Nematode at five- ten times more.
Enchitreids are the most numerous organisms in the soil. These are small annelids 5-30 mm long. Their number per 1 m2 is from 2 to 10, and in meadow soils- up to 120 thousand individuals. The biomass of enchytraids under favorable conditions for reproduction can reach 500 kg/ha. Enchytreids lead a mobile lifestyle. They move along the passages being made or through natural soil pores, which allows them to penetrate to a relatively large depth. Enchitreids feed on dead parts of plants, but there are also predatory species among them that eat potato nematodes.
Centipedes are representatives of the arthropod class. Their sizes range from 1.5 to 2 mm in small species and from 10 to 15 cm in the largest. The total number of centipedes in the meadow soil layer is 15-20 cm- 4873 ind./m2. In the southern warm soils, not millipedes predominate, but wood lice. According to the nature of the food, centipedes and wood lice are saprophages and predators. And all of them release their excrement into the soil, the quality is no worse than earthworms and make the same moves, thereby improving the permeability of the soil for air and water to a depth of 1 meter.
Macrofauna. This group of soil animals includes earthworms, insectivores, rodents and excavators. The most studied organisms, in terms of their role in soil formation, are earthworms. About 100 species of earthworms are found in the soils of our country, but only 16 species are widespread. The life expectancy of earthworms in natural conditions is 2-3 years. Main focus point- humus layer of the soil. Very often they go deep into the lower horizons. It is believed that in cultivated soils the number of earthworms should be at least 1.0 million individuals, and their weight should be 0.5-0.6 t/ha. Everyone understands that their number depends on the introduced organic matter, on the load of pesticides and mineral fertilizers, and on the minimum tillage.
The main food source for earthworms are plant residues and ingested soil containing organic matter and various kinds of microorganisms. In 24 hours, earthworms process such an amount of soil that is comparable to their body weight. Food residues and ingested soil after passing through the intestines are thrown onto the surface of the soil or in underground passages in the form of coprolites.- rounded lumps of soil with a diameter of 1-5 mm. In fields and meadows, earthworms annually deposit from 20 to 80 t/ha of coprolites. It is believed that the entire humus horizon of the soil where earthworms live is completely mixed in 100 years. The effect of soil mixing is of particular importance with minimal surface tillage. We contribute to a faster accumulation of organic matter in the upper horizons, and earthworms move it to the lower ones, which naturally has a positive effect on plant growth. Although more important is the aeration of the soil by the passages of the worms and the fact that they carry effective microorganisms into new soil layers.
I have listed the main representatives of the flora and fauna of the soil and their quantitative role in the accumulation of soil fertility. But it's more important to understand something else. Living organisms that inhabit the soil do not exist on their own, but are part of biological associations, or rather ecosystems. Soil ecosystems, in terms of their laws and functioning, almost do not differ from ordinary terrestrial and aquatic ecosystems that are familiar to us. They have all the main structural components interconnected by direct and reverse material and energy bonds.
I will give a small example from the life of the microworld invisible to us. So, algae have a positive effect on the vital activity of bacteria and protozoa. Enrichment of soil with cyanobacteria contributes to an increase in the number and biomass of protozoa by 1.5-2 times, and their species such as ciliates by 4-8 times. Algae also stimulate the growth of most fungi. Fungi, in turn, enhance the nitrogen-fixing activity of bacteria and algae being in close symbiosis with them.
The vital activity of protozoa to a large extent depends on the presence of microorganisms, which are their main source of nutrition.
Now imagine. We applied herbicides to kill only weeds and, without our eyes noticing, destroyed soil algae. And the whole chain of the most important ties collapsed from beginning to end. Bacteria, protozoa, fungi, and earthworms and all other helpers for our plants have drastically decreased in numbers along the chain. And this niche was occupied by pests and diseases.
Another example. Certain types of microorganisms, and in particular algae, eaten by soil animals are not digested in their bodies and are discarded with excrement. Being in this environment, they use the easily available nutrients contained in it, and therefore develop very quickly. This is how the selection and reproduction of selected individuals occurs.
I will end with a quote from one clever book:
“… The excretory function at the roots depends on many environmental factors. But the most remarkable thing is that it can be stimulated by microorganisms of the rhizosphere. This suggests the existence of a very close relationship between plants and microorganisms, which goes beyond simple interaction. They can be considered as a single system consisting of two blocks, between which there is a permanent two-way connection, allowing each of them to regulate the functions of the other to one degree or another. In other words, the excretory function of the root system of plants and microorganism cells, through which information is exchanged, should be considered as one of the evolutionary acquisitions, allowing them to be less dependent on environmental conditions ... "
(Ivanov V.P. Plant secretions and their significance in the life of phytocenoses)
Living organisms are an essential component of the soil. Their number in well-cultivated soil can reach several billion per 1 g of soil, and their total mass can be up to 10 t/ha. Most of them are microorganisms. The dominant value belongs to plant microorganisms (bacteria, fungi, algae, actinomycetes).
soil structure. The soil rich in microorganisms is glued together by mineral and organic colloidal particles into small lumps that do not fit tightly to each other, which allows air to penetrate deep into the soil, and water not to linger on the surface and wet the soil. Clay rich in humus crumbles into small lumps.
Soil structure is the most important condition for the synthesis of humus, increasing soil fertility, and its health.
The passages of microscopic and earthworms, the cavities of dead plant roots also improve the aeration and permeability of the soil. The addition of lime to heavy clayey acidic soil also improves its permeability and structure.
The task of the gardener is not to destroy the structure of the soil during its cultivation, and to additionally use agricultural techniques that improve the structure of the soil.
Animal organisms are represented by protozoa (flagellates, rhizomes, ciliates), as well as worms. Mollusks and arthropods (arachnids, insects) are quite widespread in the soil.
Soil organisms destroy the dead remains of plants and animals entering the soil. One part of the organic matter is completely mineralized, and the products of mineralization are assimilated by plants, while the other part passes into the form of humic substances and living bodies of soil organisms.
Some microorganisms (nodule and free-living nitrogen-fixing bacteria) assimilate atmospheric nitrogen and enrich the soil with it.
Soil organisms (especially fauna) contribute to the movement of substances along the soil profile, thorough mixing of the organic and mineral parts of the soil.
The most important function of soil organisms is the creation of a strong cloddy structure of the soil of the arable layer. The latter to a decisive extent determines the water-air regime of the soil, creates conditions for high soil fertility.
Finally, soil organisms secrete various physiologically active compounds in the course of their vital activity, contribute to the transfer of some elements into a mobile form and, conversely, to the fixation of others into a form inaccessible to plants.
In cultivated soil, the functions of soil organisms are reduced to maintaining an optimal nutritional regime (partial fixation of mineral fertilizers with subsequent release as plants grow and develop), soil structuring, and elimination of unfavorable environmental conditions in the soil.
In intensive agriculture, environmental conditions can sometimes decisively determine effective soil fertility. There are close and diverse links between all soil organisms in it. Moreover, this entire system is in a state of continuously changing equilibrium. Some groups of microorganisms make simple food requirements, others are complex. Between some groups there are symbiotic (mutually beneficial) links, between others - antibiotic. Microorganisms in the latter case release substances into the soil that inhibit the development of other microorganisms.
Of practical importance is the ability of some microorganisms to have a detrimental effect on representatives of phytopathogenic microflora.
It is possible to enhance the activity of desirable microorganisms by introducing organic matter into the soil. In this case, there is an outbreak in the development of soil saprophytes, which, in turn, stimulate the development of microorganisms that inhibit phytopathogenic species. For the normal functioning of soil organisms, first of all, energy and nutrients are needed. For the vast majority of microorganisms, such an energy source is the organic matter of the soil. Therefore, the activity of soil microflora mainly depends on the input or presence of organic matter in the soil.
To assess the activity of soil biota, the indicator is used soil biological activity. By biological activity is understood, in some cases, the total biogenicity of the soil, determined, as a rule, by counting the total number of soil microorganisms. If we keep in mind the imperfection of the methods used in this case, and the small multiplicity of determinations over time, then the results of the analysis give an approximate picture of the biological activity of the soil.
Another point of view regarding the methods for determining the biological activity of the soil is to take into account the results of the activity of soil organisms. This approach is especially important in agronomy. However, it is methodologically difficult to bring the exceptionally diverse activity of soil flora and fauna to a common denominator.
The most universal indicator of the activity of soil organisms is their production of carbon dioxide. Therefore, taking into account the carbon dioxide released by the soil is paramount among other biochemical methods for determining the biological activity of the soil.
Soil structure- an important indicator of the physical condition of fertile soil. It determines the favorable structure of the arable layer of the soil, its water, physico-mechanical and technological properties and water-hydrological constants. Particles of the solid phase of the soil, as a rule, stick together into lumps (aggregates). The ability of soil to disintegrate into aggregates of various sizes is called structure. In soil science, soil structure is an important morphological feature: the size of the aggregates is used to judge the genetic characteristics of both the entire soil and its individual horizons. According to the classification of S. A. Zakharov, the following types of structure are distinguished: lumpy, lumpy, nutty, granular, columnar, prismatic, platy, lamellar, leafy, scaly.
Chernozems, for example, in their natural state are characterized by a distinct granular structure, gray forest soils are nutty. Well-cultivated sod-podzolic soils acquire a lumpy structure, while uncultivated podzols are distinguished by platy and leafy.
In agriculture, the following classification of structural aggregates has been adopted: lumpy structure - lumps of more than 10 mm, macrostructure - from 0.25 to 10 mm, microstructure - less than 0.25 mm. Favorable sizes of macro- and micro-aggregates for arable soil are largely conditional. In more humid conditions, the optimal sizes of structural aggregates increase, while in drier conditions they decrease. However, under conditions of erosion hazard, an increase in the size of aggregates up to 1-2 mm in diameter acquires special agronomic importance in arid regions.
The formation of structural aggregates in the soil, according to N. A. Kachinsky, occurs as a result of the following processes: mutual precipitation (coagulation) of colloids, coagulation of colloids under the influence of electrolytes. These processes, however, manifest themselves against the background of more general physical-mechanical, physico-chemical and biological factors of structure formation.
Of great importance is the mechanical separation of the soil mass into lumps (aggregates), which under natural conditions occurs under the influence of the root systems of plants, the vital activity of the soil biota, under the influence of periodic freezing - thawing, moistening and drying of the soil, and in cultivated soils and the impact of tillage tools. .
The state of the soil structure directly determines the parameters of the structure of the arable layer. The following conditions are necessary for the formation of a strong soil structure: a sufficient amount of mineral and organic colloids; sufficient content of alkaline earth bases in the soil; favorable hydrothermal conditions in the soil; impact on the soil mass of plant roots; impact on the soil of soil fauna (earthworms, insects, excavators, etc.).
The structural state is the most reliable, integral indicator of soil fertility (its agrophysical factors).
soil fertilization determines the interaction of introduced substances with the soil and the impact of soil microorganisms, which determine various transformations that affect the ability of fertilizer to move in the soil, the solubility of the food elements contained in it and their availability to plants. These transformations depend on the properties of the soil and fertilizers. For example, on sandy soils, the rate of decomposition of incoming organic fertilizers, with the equality of other factors, is higher than on loamy and clayey ones.
Soil types
Different types of soils were formed in connection with the predominance of one or another soil-forming factor. The following soils are distinguished on the territory of Russia:
tundra soils
weakly podzolic and podzolic soils (comprise most of the soils of Russia).
Gray forest soils (typical for the more southern region of Russia).
Chernozems (beginning in the Tambov region) occupy a small area of chestnut soils.
Brown, solonchak soils are characteristic of the southern steppe and desert areas.
The concept of the diversity of the living world for a long time was limited to dividing it into two kingdoms: plant and animal organisms, respectively, the flora and fauna of the Earth. This idea came from Aristotle and was "legitimized" in the "System of Nature" by K. Linnaeus. The main distinguishing features of these kingdoms were in the type of nutrition (heterotrophic and holozoic in animals, autotrophic and osmotrophic in plants); the presence of a rigid cell wall (in plants) or its absence (in animals); mobile or immobile lifestyle. And although these signs were not always found in organisms attributed to these two kingdoms, nevertheless, the bulk of their representatives corresponded to this characteristic. Microscopic organisms were divided between these two kingdoms as follows: algae, fungi and bacteria were classified as plants, protozoa as animals. In a more detailed study of unicellular microscopic organisms, difficulties arose in dividing them into animals and plants: in some,
combinations of features characteristic of representatives of both the one and the other kingdom. For example, some unicellular flagellates contain chlorophyll and are capable of photosynthesis like plants, while at the same time, by the nature of the organization of the cell, they should be classified as protozoa; slime molds (myxomycetes) in the amoeba stage are phagotrophs like protozoa, and in the stage of formation of fruiting bodies they are similar to fungi.
To avoid the difficulties that arise in the classification of such objects, it was proposed to create a third kingdom of wildlife - the kingdom of protists (E. Haeckel), which included algae, protozoa, fungi and bacteria. The result was a mixed kingdom, the main characteristic of which was the relative simplicity of biological organization. From an evolutionary standpoint, it is clear that the members of this kingdom are the descendants of those organisms that existed before the division of animals and plants into two major branches of the development of life.
A turning point in the ideas about the diversity and evolution of the living world was the establishment of differences in the fine structure of all cells, the discovery of the prokaryotic and eukaryotic types of cellular organization. Cytological differences initially detected using an electron microscope, mainly in the nuclear apparatus, were then supported by biochemical data on the composition
cell walls and the mechanisms of operation of cell components that provide the synthesis of informational macromolecules. The gap between Procaryota (pre-nuclear organisms) and Eucaryota (true nuclear organisms) turned out to be much larger than the differences between plants and animals. At the same time, the kingdom of protists turned out to be divided: bacteria and blue-green algae moved to prokaryotes, and protozoa, fungi and other algae - to eukaryotes.
Based on the two main characteristics of a living thing - the type of nutrition and the type of structure - then their different combinations appear
Rice. 1. Kingdoms of wildlife
in the seven Groups of organisms that exist on Earth, from which four kingdoms of living nature are formed (Fig. 1). Plants (Plantae) unite photosynthetic eukaryotic organisms (from unicellular algae to vascular plants with a tissue structure of the body). Primary producers of organic substances. Animals (Animalia) combine eukaryotic organisms with a holozoic type of nutrition from unicellular protozoa to complex organisms with a tissue structure of the body and the presence of specialized organs. Consumers of organic substances at different trophic levels. Mushrooms (Mycota) are eukaryotic organisms with an osmotrophic type of nutrition, unicellular and mycelial, sometimes forming false tissues. Major decomposers of organic matter.
Prokaryotes (Procaryotae) - pre-nuclear microscopic organisms, mainly unicellular and mycelial. According to the type of nutrition, they are divided into two groups: phototrophic and osmotrophic (in other words, autotrophs and heterotrophs). Accordingly, in ecological chains they act as either producers or decomposers.
The four-kingdom system is also preserved when all unicellular eukaryotes are combined into one kingdom of protests (Protista). Algae, fungi and protozoa get into it. Between these groups there are intermediate forms that blur the boundaries between them. The loss of pigments in unicellular algae makes them indistinguishable from fungi; flagellar forms of algae and protozoa are difficult to unequivocally attribute to one or the other; slime molds in the vegetative stage of amoebae feed holozoically, but form sporangia with spores at the stage of reproduction, like fungi.
Representatives of all the kingdoms of living nature live in the soil, no matter how many of these kingdoms we single out. The root systems of higher plants develop in the soil, lower plants - algae - live on the surface of the soil and in the upper layers of the soil layer. Animals of different size groups use the soil as a habitat in different ways: some live in it permanently, populating its pores, interaggregate spaces and water films; others make passages, burrows and caves in the soil, greatly changing its composition; still others only temporarily go into the soil, using it as a shelter or a place where the stage of winter dormancy takes place. The protozoa show their activity mainly in the water phase of the soil. Microscopic organisms - fungi, bacteria, actinomycetes - attach themselves to the surface of soil particles and form more or less complex growths on them - colonies. Some bacteria lead a mobile lifestyle, actively moving in aqueous solutions that fill the capillaries.
The totality of the living inhabitants of the soil is called the soil biota. This term has no taxonomic meaning and does not carry any ecological burden. Biota is a collective concept for the whole complex of organisms living in the soil, sometimes called edaphon. This complex is extremely diverse and differs in soils of different types.
Below we consider soil biota by taxonomic groups in order of their ecological importance in the biological cycle of substances: from producers to decomposers.
More on the topic Chapter 1 SOIL BIOTA:
- Chapter Two PARTICIPATION OF SOIL MICROORGANISMS IN THE TRANSFORMATION OF SUBSTANCE AND ENERGY IN THE BIOSPHERE
- Chapter 2 PARTICIPATION OF SOIL MICROORGANISMS IN THE CYCLES OF BASIC NUTRIENTS IN THE BIOSPHERE AND SOIL FORMATION PROCESSES
Transgenic plants and soil biota
A.G. Viktorov, Candidate of Biological Sciences, Institute of Ecology and Evolution named after V.I. A.N. Severtsov RAS
The first pest-resistant plants created using genetic engineering methods were introduced into cultivation in the 90s of the last century. These genetically modified plants (Bt-cultures) carry the genes of the gram-positive aerobic spore-forming bacterium Bacillus thuringiensis, which synthesizes parasporal (localized next to the spore) crystalline formations containing d-endotoxins - Cry proteins that kill insect larvae of different orders. I note that preparations from a mixture of cells, spores and parasporal crystals have been used for more than half a century (the first industrial insecticide "Sporein" was created in France in 1938). Since then, they have been considered one of the most environmentally friendly plant protection products, since this class of pesticides is toxic to warm-blooded animals only at concentrations several thousand times higher than the doses used in a single field treatment.
Currently, about thirty Bt crops are used in agriculture. The most popular of them are corn, cotton, potatoes, canola hybrid (from the English canada oil low acid - Canadian slightly acidic oil), rice, broccoli, peanuts, eggplant, tobacco. Most varieties of transgenic corn carry the Cry1Ab protein gene, which protects against a dangerous pest - the larvae of the corn or stem borer (Ostrinia nubilalis).
In 2001, genetically modified crops already occupied more than 12 million hectares in the world, with about half of them accounted for by transgenic corn. 99% of all Bt crops are grown in four countries: USA, Argentina, Canada and Chile. In the USA, the field area of Bt-corn in 2000 was more than 8 million hectares (about a quarter of the plantations), and Bt-cotton - 2.4 million hectares (about half of the crops). The economic benefit of such plants is clear: according to the US Environmental Protection Agency, the use of only Bt-crops in this country leads to an annual reduction in the use of synthetic insecticides on an area of about 3 million hectares and saves $ 2.7 billion. USA .
Until recently, ecologists warned about the possible negative impact of transgenic crops on the environment. Proponents of the genetic modification of plants, on the contrary, convinced of their complete environmental safety, based on the results of laboratory tests and the experience of growing these crops in natural conditions. (As it turned out later, the methods and test objects used in some laboratory experiments were not adequate to the tasks set, but more on that later.) Only now, a decade after the start of the industrial cultivation of transgenic crops, it becomes more or less obvious what kind of damage they can inflict on the environment.
There is growing evidence that the use of Bt plants may have a long-term negative effect, the economic impact of which is still difficult to assess. First, Bt corn produces 1500 to 2000 times more endotoxin than a single field treatment with chemicals containing Bt toxin. Secondly, the cultivation of Bt-corn leads to the accumulation of Bt-toxins in the soil as a result of the action of many factors: root excretion, pollen deposition, decomposition of plant residues. Thirdly, the decomposition of transgenic plants is much slower than conventional crops, and the biological activity of soils occupied by genetically modified plants is noticeably lower than in the control plots.
Bt toxins in soil
After harvesting transgenic corn, about ten percent of Bt toxins remain in crop residues in the fields. And only with their decomposition does the degradation of Cry-proteins occur in vivo. According to Swiss researchers, the concentration of Cry1Ab toxin in plant residues decreases sharply (to 20-38% of the amount in living plants) two months after harvest and remains at about the same level during the winter. Only with the onset of spring does the further degradation of Bt-toxin begin, however, even after 200 days, 0.3% of its initial amount remains in the fields. The maximum period during which the Cry-proteins that are in the soil as a result of root excretion and decomposition of plant residues are preserved reaches 350 days. Bt-toxins remain biologically active for such a long time (actually up to a year) due to the fact that they are in a bound state with surface-active soil particles (clay, humus, etc.); this is what protects them from decomposition by microorganisms.
These results were obtained relatively recently and are fundamentally different from earlier ones carried out in the laboratory, when it was found that 50% of Bt toxins decompose one and a half days after entering the soil and 90% within 15 days. If the plant residues were not in contact with the soil, then 50% degradation of Cry proteins was observed within 25.6 days, and 90% - 40.7 days. Such strong differences in the rate of decomposition of Bt toxins are obviously due to the fact that under laboratory conditions, experiments were carried out at a constant room temperature, while in nature, except for the cold winter period, characteristic of the middle zone, where transgenic corn mainly grows , there are also diurnal temperature fluctuations. In addition, in laboratory experiments, corn leaves were ground, sieved and lyophilized, which provided a significantly larger area for colonization by microorganisms. Naturally, nothing like this happens in nature, and it is clear that it is necessary to extrapolate the results of laboratory experiments with Bt toxins to natural conditions with extreme caution.
Although the input of Cry proteins into the soil with secretions from the roots of transgenic plants is not as high as after the decomposition of plant residues left in the fields after harvesting, this factor cannot be disregarded. It is interesting to note that if the root shoots of canola, tobacco, and cotton do not release Bt toxins at all, then all 12 studied transgenic corn varieties obtained using three independent genetic engineering operations (Bt11, MON810, and Bt176) produce Cry proteins almost in the same quantities. In addition, the insecticidal activity of corn secretions was the highest - significantly higher than that of rice and potatoes. Although a certain amount of Cry proteins can enter the soil as a result of peeling or mechanical damage to the roots, it is with their secretions that the main part of Bt toxins enters the soil. In support of this, it suffices to say that no damage to the root surface was noted in corn, rice, and potatoes grown in hydroponics; nevertheless, Cry proteins were still recorded in the nutrient solution.
lignin
It has been noted that plants with a high content of Bt toxins are not attractive even to those phytophages for which these toxins are not poisonous. So, in experiments with the cellar, or rough, woodlice (Porcellio scaber), which were offered eight varieties of corn (two transgenic and six isogenic control lines), it turned out that this animal clearly prefers non-transgenic plants. In addition, it is known that the plant remains of transgenic plants decompose much more slowly compared to non-genetically modified isogenic lines. The reasons for this are currently being studied. It is assumed that this is due to the increased content of lignin in transgenic plants. Perhaps this also explains their food unattractiveness, however, unfortunately, the authors did not investigate the relationship between these varieties of corn and their lignin content.
Lignin is a high-molecular compound of aromatic nature - the main structural component of plants, filling the space between cells and "gluing" their primary membranes. It is lignin that provides the strength and rigidity of plant structures, as well as their water resistance. On the one hand, the increased content of lignin complicates the "work" of phytophages, on the other hand, it slows down the processes of decomposition of plant residues in the soil. During the decomposition of lignin, toxic low-molecular decomposition products (phenols, methanol, carboxylic acids) are released into the environment.
The content of lignin in the stems of Bt maize varieties is 33-97% higher than in its isogenic non-transgenic lines. A large scatter of data is associated with different lignin content in the three main lines of transgenic maize. An excess of lignin was also manifested at the morphological level. Vascular bundles and surrounding sclerenchyma cells containing lignin were almost two times thicker in Bt plants than in isogenic nontransgenic lines (21.5±0.84 mm and 12.4±1.14 mm, respectively). An increased accumulation of lignin is typical only for the stems of Bt-corn, while its amount in the leaves is approximately the same as in ordinary plants.
In addition, another curious circumstance was revealed: there was more lignin in corn grown in natural conditions than in laboratory ones. This once again confirms that a transgenic plant develops differently in an artificial environment than in nature.
As a result of further studies, it turned out that an excess of lignin is characteristic not only of Bt maize, but is a common property of all transgenic plants. In various genetically modified crops (rice, tobacco, cotton and potatoes) there is 10-66% more lignin than in their corresponding non-genetically modified isogenic lines.
earthworms
One of the main utilizers of plant litter in the middle lane is earthworms, mainly from the Lumbricidae family. They are found in almost all natural and anthropogenic ecosystems of the temperate zone and dominate them in terms of biomass (their abundance is especially high in the forest-steppe, mixed and broad-leaved forests - more than 300 individuals per 1 m2). Penetrating the soil with passages, earthworms loosen it, promoting aeration and moisture at depth, mix the soil layers, accelerating the decomposition of plant residues and thereby increasing soil fertility. The volume of soil carried by these animals ranges from 2 to 250 t/ha per year. The vertical distribution of earthworms along the soil profile is determined, on the one hand, by their ecology, and, on the other hand, by a complex of abiotic factors such as temperature, soil moisture, and the vertical gradient of organic matter distribution.
Toxins can affect earthworms in different ways, depending on the type of Lumbricidae and their stage of development. Juvenile individuals, unable to go deep into the soil, suffer from pollutants more than mature ones. But one of the largest species of Lumbricidae of the middle zone - the big creep (Lumbricus terrestris) - oddly enough, is also in the "risk group". The fact is that individuals of this species, hiding in deep (up to 3 m) burrows during the day, come to the surface of the soil at night for food - plant litter (in Russia, for such a lifestyle, this cosmopolitan received the popular name "big creep"). In fairness, we note that a small part of their diet is made up of plant roots. During such night journeys, some individuals can overcome up to 19 m. Approximately every third route ends in a hole, and every fourteenth route also has holes at the beginning of the path. In different ecosystems, during several autumn months, these earthworms are able to carry almost all plant litter into their burrows. This does not mean at all that lumbricides immediately eat everything, they store a significant part of their food in burrows and consume it as plant residues partially decompose. It is these features of the ecology of a large creep that determine the high level of its contact with both pollutants settling in the fields and with transgenic plants.
Lumbricides develop in the thickness of the soil and, of course, react to changes in its chemical composition, in particular, the ingress of pollutants that are able to penetrate into their body through the covers. Given the characteristics of nutrition, earthworms can swallow soil particles and the toxins contained in them, which means they can be exposed to them both from the outside and from the inside.
Surprisingly, detailed studies of the toxicity of Cry proteins to earthworms have not yet been carried out. True, about half a century ago, when testing the toxicity of Thuricide, containing B. thuringiensis var. kurstaki, it was found that only very high concentrations (10 thousand times higher than those recommended for field cultivation) caused 100% mortality of L. terrestris laboratory populations within two months. It would seem that these data are only indirectly related, but the lethal doses were only five to ten times higher than the concentration of Bt toxins in living transgenic plants. Histological studies of the dead Lumbricidae showed that the bacteria penetrated almost all tissues of the worms, where they sporulated and formed crystals. Later, such an unusual pathology was explained by the fact that diatomaceous earth was used in the experiments, which, damaging the intestinal epithelium, contributed to the penetration of bacteria as a whole (the space between the body wall and internal organs) of earthworms.
In another series of experiments, the effect of pesticides containing Bt-toxin on the earthworm Dendrobaena octaedra was studied: a ten-week exposure to the toxin at doses a thousand times higher than the field and approximately equal concentrations of toxins in living plants led to a significant inhibition of growth and reproduction, as well as more high mortality of worms. Unfortunately, in these experiments, a species was used that has nothing to do with the fields (usually it lives in the forest floor) and cannot encounter transgenic crops under natural conditions.
One of the first ecotoxicological experiments to study the effect of transgenic plants on earthworms was a standard laboratory test using artificial soil and a dung worm (Eisenia fetida). It turned out that extracts of transgenic maize leaves containing Bt-toxin did not affect the survival and development of these lumbricides in any way - they all survived until the end of the 14-day experiment and did not differ in body weight from control animals. According to the calculations of the authors, the concentration of Bt-toxin used in the experiment (0.35 mg of CryIA(b)-proteins per 1 kg of soil) was approximately 785 times higher than that which could be formed in the soil after harvesting. These results would make sense if the choice of earthworm species was adequate to the goals set. The authors did not take into account that E. fetida, like D. octaedra, does not encounter transgenic crops under natural conditions. Not to mention the fact that the dung worm, unlike the soil species proper, does not swallow soil particles, but feeds on decaying organic matter, so it is not clear how much Bt-toxins got into its digestive system and whether it got there at all.
40-day observations of laboratory populations of L. terrestris living in soil in which seeds of transgenic corn were germinated or its leaves were added did not reveal significant changes in either body weight or mortality of large creeps, although Bt toxins were found in them. intestines and castes (excrement). When the worms were transferred to clean soil, their intestines were cleared of the toxin within one to two days. Unfortunately, the authors of this work did not evaluate the effect of Bt toxins on the reproduction of Lumbricidae, as well as on juvenile, more sensitive to toxins, individuals. In addition, for such a large earthworm living for more than one year as a large creep, a 40-day period is clearly insufficient to detect sublethal effects. In another, somewhat later, similar experiment, but lasting already 200 days, it turned out that the body weight of L. terrestris fed on transgenic plant residues decreased by an average of 18%, while in the control group it increased by 4%.
Unfortunately, the migration of Bt toxins in trophic chains, in which earthworms serve as a food base for many predatory invertebrates, birds, and mammals, has not yet been studied. For example, in England, in the diet of red foxes (Vulpes vulpes), a large creep is on average 10-15%, and in areas where these earthworms are especially numerous, up to 60%. The Tawny Owl (Strix aluco), which can catch more than 20 worms in an hour, does not disdain large crawls. A special love for L. terrestris has also been noted in the European badger (Meles meles); more than 20 years ago, they were even considered specialized predators of earthworms. Subsequently, the hypothesis was rejected, but in fairness, we note that in some way this predator still has specialization - it manifests itself in the technique of capturing food.
For soil microorganisms (both pure and mixed cultures), the toxicity of Cry proteins was not revealed; the number of bacteria and fungi in soils containing the biomass of genetically modified and non-transgenic maize did not differ statistically. However, in experiments with soil microcosms in which soil invertebrates were absent, it was shown that in this case, too, the biodegradation of Bt crops (corn, rice, tobacco, cotton, and tomatoes) occurs much more slowly than in the control. This was evidenced by a significantly lower amount of carbon leaving the experimental soil microcosms in the form of CO2 compared to the control.
The reduced rate of degradation of transgenic plant residues requires further and comprehensive study, since the potential damage from this inherent property of Bt crops may have long-term environmental consequences. The peculiarities of the migration of Cry proteins along food chains require even closer attention. Finally, there is increasing evidence that agricultural pest populations are beginning to develop resistance to Bt toxins and are beginning to feed on transgenic plants.
The detection of Bt toxins in the root exudates of corn, rice, and cotton and their long-term persistence in the soil also suggests that special precautions must be taken before plants and animals genetically modified for the production of drugs (antibiotics, vaccines, hormones) , enzymes) and other biologically active substances will leave the walls of laboratories and find themselves in less controlled conditions of industrial production. Unlike Bt plants, the targets of these compounds are not insects, but mammals, including humans. Almost all of these substances are xenobiotics, but their ability to persist in the environment has not been sufficiently studied. It is clear, therefore, that the potential damage of growing transgenic plants synthesizing them in the environment cannot be even approximately estimated.
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For the preparation of this work, materials from the site http://vivovoco.rsl.ru were used.