Introduction
1. Habitats and environmental factors
1.1 Air environment
1.2 Aquatic environment
1.3 Environmental factors
2. Adaptation
2.1 Plant adaptation to atmospheric pollution
2.2 Plant adaptation to soil salinity
2.2.1 Plants and heavy metals
2.3 Plant adaptation to biotic factors
2.4 Plant adaptation to abiotic factors
2.4.1 Temperature effect
2.4.2 Effect of light on plants
3. Research part
Conclusion
Used information resources when performing educational and research work
10.Sbio. info First bio community: information portal: [Electronic. resource] // Biotic factors of the environment and the types of interactions of organisms caused by them [website] Access mode: www.sbio. info/page. php? id=159 (04/02/10)
Photo No. 1. Aspen leaf from the park.
Photo #2. A sheet located next to the roadway.
Photo #3. Dust on sticky tape from a leaf from the park.
Photo #4. Dust on sticky tape from a sheet next to the roadway.
Photo #5. Lichen on a tree trunk in a forest park.
Sexual reproduction in seed plants, which include flowering and gymnosperms, is carried out using seeds. In this case, it is usually important that the seeds are at a sufficiently remote distance from the parent plant. In this case, it is more likely that young plants will not have to compete for light and water both among themselves and with an adult plant.
Angiosperms (they are flowering) plants in the process of evolution of the plant world solved the problem of seed distribution most successfully. They "invented" such an organ as the fetus.
Fruits serve as an adaptation to a certain method of dispersal of seeds. In fact, most often the fruits are distributed, and the seeds along with them. Since there are a lot of ways to distribute fruits, there are many varieties of fruits. The main methods of distribution of fruits and seeds are as follows:
with the help of the wind
animals (including birds and humans),
self-spreading,
with the help of water.
The fruits of plants that are dispersed by the wind have special devices that increase their area, but do not increase their mass. These are various fluffy hairs (for example, poplar and dandelion fruits) or pterygoid outgrowths (like maple fruits). Thanks to such formations, the seeds soar in the air for a long time, and the wind carries them farther and farther from the parent plant.
In the steppe and semi-desert, plants often dry up, and the wind breaks them off at the root. Rolled by the wind, withered plants scatter their seeds over the area. Such "tumbleweed" plants, one might say, do not even need fruits to spread seeds, since the plant itself spreads them with the help of wind.
With the help of water, the seeds of aquatic and semi-aquatic plants are distributed. The fruits of such plants do not sink, but are carried away by the current (for example, in alder growing along the banks). And it doesn't have to be small fruits. In the coconut palm, they are large, but light, so they do not sink.
Adaptations of plant fruits to distribution by animals are more diverse. After all, animals, birds and humans can distribute fruits and seeds in different ways.
The fruits of some angiosperms are adapted to cling to the fur of animals. If, for example, an animal or man will pass next to the burdock, then several prickly fruits will catch on to it. Sooner or later, the animal will drop them, but the burdock seeds will already be relatively far from their original place. In addition to burdock, an example of a plant with hook fruits is a string. Its fruits are of the achene type. However, these achenes have small spikes covered with denticles.
Succulent fruits allow plants to distribute their seeds with the help of animals and birds that eat these fruits. But how do they spread them if the fruit and seeds along with it are eaten and digested by the animal? The fact is that it is mainly the juicy part of the pericarp of the fetus that is digested, but the seeds are not. They come out of the digestive tract of the animal. The seeds are far from the parent plant and are surrounded by droppings, which, as you know, are a good fertilizer. Therefore, a juicy fruit can be considered one of the most successful achievements in the evolution of wildlife.
Man played a significant role in seed dispersal. So the fruits and seeds of many plants were accidentally or deliberately brought to other continents, where they could take root. As a result, now we can, for example, observe how plants characteristic of Africa grow in America, and in Africa - plants whose homeland is America.
There is a variant of seed distribution using spreading, or rather self-spreading. Of course, this is not the most effective method, since the seeds are still close to the mother plant. However, this method is often observed in nature. Usually seed scattering is characteristic of fruits of the pod, bean and box type. When a bean or pod dries up, its wings are twisted in different directions, and the fruit cracks. Seeds fly out of it with little force. This is how peas, acacia and other legumes spread their seeds.
The fruit of the box (for example, in a poppy) sways in the wind, and seeds spill out of it.
However, self-spreading is not limited to dry seeds. For example, in a plant called mad cucumber, seeds fly out of their juicy fruit. It accumulates mucus, which, under pressure, is ejected along with the seeds.
Sunlight is one of the most important environmental indicators for plant life. It is absorbed by chlorophyll and used in the construction of primary organic matter. Almost all houseplants photophilous, i.e. thrive best in full light, but vary in shade tolerance. Taking into account the relation of plants to light, they are usually divided into three main groups: photophilous, shade-tolerant, shade-indifferent.
There are plants that adapt quite easily to sufficient or excess light, but there are also those that develop well only under strictly defined light parameters. As a result of the adaptation of the plant to low light, its appearance changes somewhat. The leaves become dark green and slightly increase in size (linear leaves lengthen and become narrower), the stem begins to stretch, which at the same time loses its strength. Then the growth gradually decreases, because the production of photosynthesis products, going to the building bodies of the plant, sharply decreases. With a lack of light, many plants stop blooming. With an excess of light, chlorophyll is partially destroyed, and the color of the leaves becomes yellow-green. In strong light, plant growth slows down, they turn out to be more squat with short internodes and wide short leaves. The appearance of a bronze-yellow leaf color indicates a significant excess of light, which is harmful to plants. If prompt action is not taken, burns may occur.
The effect of ionizing radiation is manifested in the effect of radiation on a plant organism at different levels of organization of living matter. The direct action consists in the radiation-chemical ionization of molecules together with the absorption of radiation energy, i.e. puts molecules in an excited state. Indirect exposure is accompanied by damage to molecules, membranes, organelles, cells as a result of exposure to water radiolysis products, the number of which sharply increases as a result of irradiation. The effectiveness of radiation damage depends significantly on the oxygen content in the environment. The lower the oxygen concentration, the lower the damage effect. In practice, it is generally accepted that the limit of lethal oxygen doses characterizes the radioresistance of organisms. In an urban environment, plant life is also affected by the location of buildings. From this we can conclude that plants need light, but each plant is photophilous in its own way.
Plant development is closely related to environmental conditions. The temperatures characteristic of a given area, the amount of precipitation, the nature of soils, biotic parameters and the state of the atmosphere - all these conditions interact with each other, determine the nature of the landscape and the type of plants.
Each contaminant affects plants in a different way, but all contaminants affect some basic processes. First of all, systems that regulate the flow of pollutants are affected, as well as chemical reactions responsible for the processes of photosynthesis, respiration and energy production. In the course of my work, I realized that the plants that grow near the roads are significantly different from the plants that grow in parks. Dust that settles on plants clogs pores and interferes with respiration processes, and carbon monoxide leads to yellowing, or discoloration of the plant and dwarfing.
I conducted my research on the example of aspen leaves. In order to see how much dust remains on the plant, I needed sticky tape, which I glued to the outside of the leaf. The leaf from the park is slightly polluted, which means that all its processes are functioning normally. [cm. application, photo No. 1,3]. And the leaf, which was in close proximity to the road, is very dirty. It is smaller than its normal size by 2 cm, has a different color (darker than it should be), and therefore has been exposed to atmospheric pollutants and dust. [cm. application, photo No. 2,4].
Another indicator of environmental pollution is the absence of lichens on plants. In the course of my research, I found out that lichens grow on plants only in ecologically clean places, for example: in the forest. [cm. application, photo No. 5]. It is difficult to imagine a forest without lichens. Lichens settle on the trunks, and sometimes on the branches of trees. Lichens grow especially well in our northern coniferous forests. This testifies to clean air in these areas.
Thus, we can conclude that lichens do not grow at all in the parks of large cities, tree trunks and branches are completely clean, and outside the city, in the forest, there are quite a lot of lichens. The fact is that lichens are very sensitive to air pollution. And in industrial cities it is far from clean. Factories and factories emit many different harmful gases into the atmosphere, it is these gases that destroy lichens.
In order to stabilize the situation with pollution, we first of all need to limit the release of toxic substances. After all, plants, like us, need clean air to function properly.
Based on the research I have done and the sources I have used, I have come to the conclusion that the plant environment has environmental issues that need to be addressed. And the plants themselves take part in this struggle, they actively purify the air. But there are also climatic factors that do not have such a detrimental effect on plant life, but force plants to adapt and grow in suitable climatic conditions for them. I found out that the environment and plants interact, and without this interaction, plants would die, since all the components necessary for their life, plants draw from their habitat. Plants can help us deal with our environmental problems. In the course of this work, it became more clear to me why different plants grow in different climatic conditions and how they interact with the environment, as well as how plants adapt to life directly in the urban environment.
Genotype - the genetic structure of an individual organism, the specific set of genes that it carries.
Denaturation is a characteristic change in protein substances in their structure and natural properties when the physical and chemical conditions of the environment change: with an increase in temperature, a change in the acidity of the solution, etc. The reverse process is called renaturation.
Metabolism is a metabolism, chemical transformations that occur from the moment nutrients enter a living organism to the moment when the end products of these transformations are released into the external environment.
Osmoregulation is a set of physicochemical and physiological processes that ensure the relative constancy of the osmotic pressure (OD) of the liquids of the internal environment.
Protoplasm - the contents of a living cell, including its nucleus and cytoplasm; the material substratum of life, the living substance of which organisms are composed.
Thylakoids are membrane-bound compartments within chloroplasts and cyanobacteria. The light-dependent reactions of photosynthesis take place in the thylakoids.
Stomata - a slit-like opening (stomatal fissure) in the epidermis of above-ground organs of plants and two cells limiting it (closing).
Phytophages are herbivorous animals, which include thousands of species of insects and other invertebrates, as well as large and small vertebrates.
Phytoncides are biologically active substances formed by plants that kill or inhibit the growth and development of bacteria, microscopic fungi, and protozoa.
Photosynthesis is the formation of organic substances by green plants and some bacteria using the energy of sunlight. During photosynthesis, carbon dioxide is absorbed from the atmosphere and oxygen is released.
1. Akhiyarova G.R., Veselov D.S.: "Hormonal regulation of growth and water metabolism under salinity" // Abstracts of the participants of the 6th Pushchino school - conference of young scientists "Biology - science of the XXI century", 2002.
2. Big encyclopedic dictionary. - 2nd ed., revised. and additional - M .: Great Russian Encyclopedia, 1998. - 1456 p.: ill. Edited by Prokhorov A.M. Ch. editor Gorkin A.P.
3. Vavilov P.P. Crop production, 5th ed. - M .: Agropromizdat, - 1986
4. Vernadsky V.I., Biosphere, vol. 1-2, L., 1926
5. Volodko I.K.: “Trace elements and resistance of plants to adverse conditions”, Minsk, Science and technology, 1983.
6. Danilov-Danilyan V.I.: "Ecology, nature conservation and environmental safety" M.: MNEPU, 1997
7. Drobkov A. A.: "Microelements and natural radioactive elements in the life of plants and animals", M., 1958.
8. Wikipedia: information portal: [Electron. resource] // Habitat [website] Access mode: http://ru. wikipedia.org/wiki/Habitat (10.02.10)
9. Everything about the Earth: information portal: [Electron. resource] // Water shell [site] Access mode: http://www.vseozemle.ru/2008-05-04-18-31-40.html (23.03.10)
10.Sbio. info First bio community: information portal: [Electronic. resource] // Biotic factors of the environment and the types of relationships of organisms caused by them [website] Access mode: http://www.sbio. info/page. php? id=159 (04/02/10)
Photo No. 1. Aspen leaf from the park.
Photo #2. A sheet located next to the roadway.
Photo #3. Dust on sticky tape from a leaf from the park.
Photo #4. Dust on sticky tape from a sheet next to the roadway.
Photo #5. Lichen on a tree trunk in a forest park.
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Creating the most favorable growth conditions for each vegetable crop is more available in greenhouses, but even then not always. In the open ground, such conditions can either alternate in periods of growth (months and weeks), or be combined in a random optimal coincidence of several environmental conditions and care methods.
And, nevertheless, despite the obvious unfavorability in individual years, the plants still produce annual yields that generally satisfy the owners of gardens.
The ability of crops to produce crops in almost any combination of climatic factors and any lack of care lies in their biological adaptability to growing conditions.
Examples of such adaptations (adaptive abilities) include rapid growth (early maturity), a very deep or widely branched root system closer to the soil surface, a large number of fruit ovaries, mutually beneficial community of roots with microorganisms and others.
In addition to these, there are many other mechanisms of adaptation of plants to the prevailing external conditions and opposition to them.
They will be discussed.
Thirty years ago, Moldovan scientists, having studied 200 plant species (including the majority of vegetables), came to the conclusion that they have peculiar physiological “refrigerators” in the intercellular spaces of the leaves.
Up to 20-40% of moisture in the form of steam generated inside the leaf, and part of the steam absorbed by the leaf from the outside air, condenses (settles) on the cells of internal tissues and protects them from excessive overheating at high outdoor temperatures.
With a sharp increase in air temperature and with a decrease in moisture supply (insufficient or delayed watering), vegetable coolers intensify their activity, due to which carbon dioxide absorbed by the leaf is involved in the process, leaf temperature decreases and water consumption for evaporation (transpiration) decreases.
With a short exposure to heat, the plant will successfully cope with such an unfavorable factor.
Overheating of the sheet can occur when it absorbs excess thermal solar radiation, which is called near infrared in the spectrum of sunlight. Sufficient content of potassium in the leaves helps to regulate such absorption and prevent its excess, which is achieved by timely periodic feeding of this element.
In case of death of plants from freezing with a strong root system, dormant buds awaken in them, which under normal conditions would not have shown themselves in any way.
Developing new shoots often allow you to get yields that are not worse than without such stress.
Dormant buds also help plants recover when part of the leaf mass is poisoned (ammonia, etc.). To protect against the toxic effects of ammonia, the plant produces an additional amount of organic acids and complex nitrogen compounds, which help restore vital activity.
With any abrupt changes in the environment (stressful situations), systems and mechanisms are strengthened in plants that allow them to more rationally use the available biological resources.
They allow you to hold out, as they say, until better times.
Plants turned out to be adapted even to small doses of radioactive radiation.
Moreover, they absorb them for their own benefit. Radiation enhances a number of biochemical processes, which contributes to the growth and development of plants. And an important role in this is played, by the way, ascorbic acid (vitamin C).
The change of light time by darkness, the alternation during the day of light intensity and its spectral characteristics (due to cloudiness, dustiness of the air, and the height of the sun) forced the plants to adapt their physiological activity to these conditions.
They change the activity of photosynthesis, the formation of proteins and carbohydrates, create a certain daily and daily rhythm of internal processes.
Plants are “accustomed” to the fact that with decreasing light the temperature decreases, to the alternation of the air temperature during the day and at night, while maintaining a more stable soil temperature, to different rhythms of absorption and evaporation of water.
With a temporary lack of a number of nutrients in the plant, the mechanism of their redistribution from old leaves to young, growing and tops of the shoots operates.
The same happens with the natural death of the leaves. Thus, there is a saving food products with their secondary use.
In greenhouses, where light conditions are often worse than in open ground (due to shading by the coating, the absence of certain parts of the spectrum), photosynthesis is generally less intense than in open ground.
But greenhouse plants have adapted to compensate for it due to a more developed sheet surface And great content in chlorophyll leaves.
Under normal growth conditions, to increase plant mass and form crops, everything happens in concert and is adapted to ensure that the receipt of substances from photosynthesis is greater than their consumption for respiration.
All adaptive systems and reactions of plants to certain conditions of existence serve one goal - to maintain a constant internal state (biological self-regulation), without which no living organism can do.
And the proof of the best adaptability of any crop is its yield at an acceptable level in the most unfavorable year.
E. Feofilov, Honored Agronomist of Russia
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The harsher and more difficult the living conditions, the more ingenious and diverse the adaptability of plants to the vicissitudes of the environment. Often the adaptation goes so far that the external environment begins to completely determine the shape of the plant. And then plants belonging to different families, but living in the same harsh conditions, often become so similar in appearance to each other that it can be misleading about the truth of their family ties - hotcooltop.com.
For example, in desert areas for many species, and, above all, for cacti, the shape of the ball turned out to be the most rational. However, not everything that has a spherical shape and is studded with prickly thorns is cacti. Such an expedient design, which makes it possible to survive in the most difficult conditions of deserts and semi-deserts, also arose in other systematic groups of plants that do not belong to the cactus family.
Conversely, cacti do not always take the form of a ball or column dotted with thorns. One of the most famous cactus experts in the world, Kurt Backeberg, in his book The Wonderful World of Cacti, talks about how these plants can look like, placed in certain habitat conditions. Here is what he writes:
“The night in Cuba is full of mysterious rustles and sounds. Large bats, like shadows, silently rush past us in complete darkness, only the space around the old, dying trees glows, in which myriads of fireflies perform their fiery dance.
The impenetrable tropical night with its oppressive stuffiness tightly enveloped the earth. The long journey we had made on horseback had robbed us of our last strength, and now we, having climbed under Mosquito nets Let's try to get some rest. The ultimate goal of our expedition is the land of amazingly beautiful green cacti of the Ripsaliaceae group. But now the time has come to saddle the horses. And although we do this simple operation in the early morning, sweat literally floods our eyes.
Soon our small caravan sets off again. After several hours on the road, the greenish gloom of the virgin forest begins to gradually dissipate.
Our eyes open up to the horizon full of sunshine, completely covered with shrubs. Only in some places the tops of stunted trees rise above it, and sometimes you can see single powerful trunks crowned with huge crowns.
However, how strange the tree branches look!
They have, as it were, a double veil: swaying from the breaths of a warm surface breeze, long thread-stalks of one of the species of bromeliads (Tillandsia usneoides) hang from the branches almost to the ground, somewhat similar to long fabulous beards strewn with silver gray hair.
Between them hangs a mass of thin rope plants intertwined into balls: this is the habitat of colonies of leafless epiphytes, cacti related to ripsaliaceae. As if fleeing from the lush terrestrial vegetation, they tend to climb higher into the crowns of trees, closer to the sunlight. What a variety of forms! Here are thin thread-like stems or bulky fleshy outgrowths covered with delicate fluff, there are strongly overgrown shoots resembling ribbed chains in appearance.
The complex interweaving of climbing plants of the most bizarre forms: spiral, jagged, twisted, wavy - seems like a bizarre work of art. During the flowering period, all this green mass is hung with elegant wreaths or decorated with a variety of colors of the smallest specks. Later, the plants put on colorful necklaces of bright white, cherry, golden yellow and dark blue berries.
Cacti, which have adapted to live in the crowns of forest giants and whose stems, like vines, hang down to the ground, are widespread in the tropical forests of Central and South America.
Some of them even live in Madagascar and Ceylon.
Climbing cacti is not a striking example of the ability of plants to adapt to new living conditions? But he is not the only one among many hundreds of others. Common inhabitants of the tropical jungle are climbing and climbing plants, as well as epiphytic plants that settle in the crowns of woody plants.
All of them strive to get out of the eternal twilight of the dense undergrowth of virgin tropical forests as soon as possible. They find their way up to the light without creating powerful trunks and support systems that require huge building material costs. They calmly climb up, using the "services" of other plants that act as supports - hotcooltop.com.
In order to successfully cope with this new task, plants have invented various and technically quite advanced organs: clinging roots and leaf petioles with outgrowths on them, thorns on branches, clinging inflorescence axes, etc.
Plants have lasso loops at their disposal; special disks with the help of which one plant is attached to another with its lower part; movable cirriform hooks, first digging into the trunk of the host plant, and then swelling in it; various kinds of squeezing devices and, finally, a very sophisticated gripping apparatus.
We have already given a description of the structure of banana leaves given by G.
Haberlandt. No less colorfully he describes rattan - one of the varieties of climbing palms:
"If you get off footpath Botanical Garden in Bogor (Java Island) and go deeper into the thickets, then after a few steps you can be left without a hat. Dozens of hooks scattered everywhere will cling to our clothes and numerous scratches on the face and hands will call for greater caution and attention. Looking around and looking closely at the “grasping” apparatus of plants, in the zone of action of which we found ourselves, we found that the petioles of graceful and very complex rattan leaves have long, up to one or two meters, exceptionally flexible and elastic processes, dotted with numerous hard and, moreover, the same semi-movable spikes, each of which is a hook-hook bent and tilted back.
Any palm leaf is equipped with such a fearsome hook-shaped thorn, which is not so easy to part with what is hooked on it. The elastic limit of the "hook", consisting almost entirely of strong bast fibers, is extremely high.
“You can hang a whole bull on it,” my companion remarked jokingly, drawing attention to my attempts to at least approximately determine the weight that such a “line” is able to withstand. In many palm trees related to rattan, the elongated axes of inflorescences have become such tools for capturing.
The wind easily throws flexible inflorescences from side to side until a support tree trunk is in their way. Numerous hooks-hooks allow them to quickly and securely hook on the bark of a tree.
Firmly fixed with the help of overgrown leaves on several trees standing next to each other (often spikes in the lower part of the leaf petiole or even in the leaf sheath serve as additional means of retention), the completely smooth, snake-like trunk of the rattan, like a loach, climbs up, pushing through numerous branches , sometimes spreading to the crowns of neighboring trees, in order, in the end, to break through with young leaves to the light and rise above the crown of the supporting tree.
There is no further way for him: in vain his shoots will seek support in the air. Aging leaves gradually die off, and the palm gets rid of them. Deprived of "anchors-hooks", palm shoots slide down under the weight of their own weight until the uppermost leaves with their thorns again catch on any support.
At the foot of the trees, one can often see numerous shoots of a palm tree, twisted into loops, completely bare, without leaves, often as thick as the arm of an adult. It seems that the shoots, like snakes, are crawling around in search of a new support. In the Bogor Botanical Garden, the longest rattan trunk reaches 67 meters. Rattans 180 meters long, and sometimes even up to 300 meters long, are found in the impenetrable wilds of tropical rainforests!
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1 . Adaptivesyndromeatplantsonactionstressors
There are three main groups of factors that cause stress in plants: physical - insufficient or excessive humidity, light, temperature, radioactive radiation, mechanical influences; chemical - salts, gases, xenobiotics (herbicides, insecticides, fungicides, industrial wastes, etc.); biological - damage by pathogens or pests, competition with other plants, the influence of animals, flowering, fruit ripening. a set of adaptive reactions of the body that are of a general protective nature and arise in response to adverse effects that are significant in strength and duration - stressors. The functional state that develops under the influence of stressors is called stress. The adaptation syndrome was proposed by the Canadian physiologist-endocrinologist Hans Selye (1936). In the development of A. s. usually there are 3 stages. The 1st stage of anxiety lasts from several hours to 2 days and includes two phases - shock and anti-shock, the last of which mobilizes the body's defense reactions. During the 2nd stage A. s. - stages of resistance - the body's resistance to various influences is increased. This stage either leads to stabilization of the condition and recovery, or is replaced by the last stage of A. s. - a stage of exhaustion, which can end in the death of the organism.
In the first phase, significant deviations in the physiological and biochemical processes are observed, both symptoms of damage and a protective reaction appear. The value of protective reactions lies in the fact that they are aimed at eliminating (neutralizing) the resulting damage. If the exposure is too great, the organism dies even in the alarm stage during the first hours. If this does not happen, the reaction passes into the second phase. In the second phase, the body either adapts to new conditions of existence, or the damage intensifies. With the slow development of adverse conditions, the body adapts to them more easily. After the end of the adaptation phase, plants normally vegetate under unfavorable conditions already in an adapted state with a generally reduced level of processes. In the phase of damage (exhaustion, death), hydrolytic processes intensify, energy-forming and synthetic reactions are suppressed, and homeostasis is disturbed. With a strong stress intensity exceeding the threshold value for the organism, the plant dies. With the termination of the stress factor and the normalization of environmental conditions, the processes of reparation, i.e., restoration or elimination of damage, are switched on. The adaptation process (adaptation in the broad sense) proceeds constantly and carries out the "adjustment" of the organism to changes in the external environment within the limits of natural fluctuations of factors. These changes can be both non-specific and specific. Nonspecific are the same type of reactions of the body to the action of heterogeneous stressors or different organisms to the same stress factor. Specific reactions include responses that differ qualitatively depending on the factor and genotype. The most important nonspecific response of cells to the action of stressors is the synthesis of specific proteins.
Stress is a general non-specific adaptive response of the body to the action of any adverse factors. There are three main groups of factors that cause stress in plants: physical - insufficient or excessive humidity, light, temperature, radioactive radiation, mechanical stress; chemical - salts, gases, xenobiotics (herbicides, insecticides, fungicides, industrial wastes, etc.); biological - damage by pathogens or pests, competition with other plants, the influence of animals, flowering, fruit ripening.
2 . TypesadaptationatplantsWithexamples
Adaptation (adaptation) of a plant to specific environmental conditions is ensured by physiological mechanisms (physiological adaptation), and in a population of organisms (species) - due to the mechanisms of genetic variability, heredity and selection (genetic adaptation). Environmental factors can change regularly and randomly. Regularly changing environmental conditions (change of seasons) develop in plants genetic adaptation to these conditions. Adaptation is the process of adapting living organisms to certain environmental conditions. There are the following types of adaptation:
1. Adaptation to climatic and other abiotic factors (leaf fall, cold resistance of coniferous trees).
2. Adaptation to obtaining food and water (long roots of plants in the desert).
4. An adaptation that ensures the search and attraction of a partner in animals and pollination in plants (smell, bright color in flowers).
5. Adaptation to migrations in animals and seed dispersal in plants (wings of seeds for wind transport, spines of seeds).
Various plant species provide stability and survival in adverse conditions in three main ways: through mechanisms that allow them to avoid adverse effects (dormancy, ephemera, etc.); through special structural devices; due to physiological properties that allow them to overcome the harmful effects of the environment. Annual agricultural plants in temperate zones, completing their ontogeny in relatively favorable conditions, overwinter in the form of stable seeds (dormancy). Many perennial plants overwinter as underground storage organs (bulbs or rhizomes) protected from freezing by a layer of soil and snow. Fruit trees and shrubs of temperate zones, protecting themselves from the winter cold, shed their leaves.
Protection from adverse environmental factors in plants is provided by structural adaptations, features of the anatomical structure (cuticle, crust, mechanical tissues, etc.), special protective organs (burning hairs, spines), motor and physiological reactions, and the production of protective substances (resins, phytoncides , toxins, protective proteins).
Structural adaptations include small-leaved and even the absence of leaves, a waxy cuticle on the surface of leaves, their dense omission and immersion of stomata, the presence of succulent leaves and stems that retain water reserves, erectoid or drooping leaves, etc. Plants have various physiological mechanisms that allow them to adapt to unfavorable conditions. environmental conditions. This is the self-type of photosynthesis of succulent plants, minimizing water loss and essential for the survival of plants in the desert, etc. The ways of plants surviving in the steppe
It is known that the overwhelming majority of steppe plants are characterized by the development of strong pubescence of stems, leaves, and sometimes even flowers. Because of this, the steppe herbage has a dull, grayish or bluish color, contrasting with the bright emerald green of the meadow communities. Many representatives of the genus Euphorbia can serve as examples of widespread plant species with a bluish wax coating. A general reduction in the evaporating surface also contributes to a decrease in water consumption, which is achieved due to the development of narrow leaf blades in many steppe grasses and sedges, which, moreover, in dry weather can fold along , reducing the evaporating surface. A similar property was noted, in particular, in some species of feather grass. The reduction of the evaporating surface in many steppe plants is also achieved due to strongly dissected leaf blades. A similar phenomenon can be observed when comparing many closely related species of Umbelliferae, as well as in wormwood from the Compositae family. A number of plants solve the problem of lack of moisture by developing deep root systems, which make it possible to obtain water from deeper soil horizons and thus maintain relative independence from sudden changes in moisture that occur during the growing season. This group includes many steppe plants - alfalfa, some astragalus, kermeks, as well as a number of species from the Compositae family.
The ability of a plant to endure the action of adverse factors and produce offspring under such conditions is called resistance or stress tolerance. Adaptation (lat. adaptio - adaptation, adjustment) is a genetically determined process of formation of protective systems that ensure an increase in stability and the flow of ontogenesis in previously unfavorable conditions for it. Adaptation includes all processes (anatomical, morphological, physiological, behavioral, population, etc.). However, the key factor is the time given to the body to respond. The more time allowed for a response, the greater the choice of possible strategies.
With sudden action extreme factor the answer should follow immediately. In accordance with this, three main adaptation strategies are distinguished: evolutionary, ontogenetic, and urgent.
3 . evolutionaryadaptationatplants
Evolutionary (phylogenetic) adaptations are adaptations that arise during the evolutionary process (phylogenesis) on the basis of genetic mutations, selection and are inherited.
An example is the anatomical and morphological features of plants living in arid hot deserts of the globe, as well as in saline areas (adaptation to moisture deficiency). Biorhythms are the body's biological clock. Most of the biological rhythms in plants, animals and humans have been developed in the course of the evolution of life on Earth under the influence of various environmental factors, primarily cosmic radiation, electromagnetic fields, etc.
Phylogenetic adaptation is a process that lasts for several generations, and for this reason alone, according to Yu. Malov, it cannot be a property of one single organism. The homeostasis of an organism as a basic property is the result of phylogenetic adaptation. The uniformity of the representatives of the human species is manifested not in the strict similarity of the morphological and functional characteristics of individual individuals, but in accordance with their external environmental conditions. The difference in the structure of organs and tissues is not yet a negation of the norm. It is important whether this structure and its functions correspond to variations in the external environment. If the structure corresponds to the fluctuations of external factors, then it ensures the viability of the organism and determines its health. The content of the concept of adaptation covers not only the ability of living systems to reflect, through change, environmental factors, but also the ability of these systems in the process of interaction to create mechanisms and models for active change and transformation of the environment in which they live.
4 . ontogeneticadaptationatplants
Ontogenetic adaptation is the ability of an organism to adapt in its individual development to changing external conditions. There are the following subspecies:
genotypic adaptation - selection of a hereditarily determined (change in genotype) increased adaptability to changed conditions (spontaneous mutagenesis), phenotypic adaptation - with this selection, variability is limited by the rate of reaction determined by a stable genotype.
Ontogenetic, or phenotypic, adaptations ensure the survival of a given individual. They are associated with genetic mutations and are not inherited. The formation of such adaptations requires a relatively long time, so they are sometimes called long-term adaptations. A classic example of such adaptations is the transition of some C3 plants to the CAM type of photosynthesis, which helps conserve water, in response to salinity and severe water scarcity.
Ontogenetic adaptation is the ability of an organism to adapt in its individual development to changing external conditions. The following subspecies are distinguished: genotypic adaptation - selection of a hereditarily determined (genotype change) increased adaptability to changed conditions (spontaneous mutagenesis) phenotypic adaptation - with this selection, variability is limited by the reaction rate determined by a stable genotype. Ontogenetic or phenotypic adaptations ensure the survival of a given individual. They are associated with genetic mutations and are not inherited. A classic example of such adaptations is the transition of some C3 plants to the CAM type of photosynthesis, which helps to conserve water, in response to salinity and severe water deficiency. In plants, non-hereditary adaptive reactions - modifications - can also be a source of adaptation. Ontogeny of an individual begins from the moment of its formation. This event of an individual can be the germination of a spore, the formation of a zygote, the beginning of fragmentation of the zygote, the emergence of an individual in one way or another during vegetative reproduction (sometimes the beginning of ontogenesis is attributed to the formation of initial cells, for example, oogonia). In the course of ontogenesis, growth, differentiation and integration of parts of the developing organism occur. The ontogenesis of an individual can end with its physical death or its reproduction (in particular, during reproduction by division). Each organism in the period of individual development is an integral system, therefore, ontogenesis is an integral process that cannot be decomposed into simple constituent parts without loss of quality. The degree of possible variability during the implementation of the genotype is called the reaction norm and is expressed by the totality of possible phenotypes when various conditions environment. This determines the so-called ontogenetic adaptation, which ensures the survival and reproduction of organisms, sometimes even with significant changes in the external environment. Moisture and shade tolerance, heat resistance, cold resistance and other environmental features specific types plants were formed in the course of evolution as a result of long-term action of appropriate conditions. So, heat-loving plants and plants of a short day are characteristic of the southern latitudes, less demanding for heat and plants of a long day - for the northern ones.
5 . Urgentadaptationatplants
Urgent adaptation, which is based on the formation and functioning of shock protective systems, occurs with rapid and intense changes in living conditions. These systems provide only short-term survival under the damaging effect of the factor and thus create conditions for the formation of more reliable long-term mechanisms of adaptation. Shock defense systems include, for example, the heat shock system, which is formed in response to a rapid increase in temperature, or the SOS system, the trigger for which is DNA damage.
Urgent adaptation is an immediate response of the body to the influence of an external factor. Long-term adaptation is a gradually developing response of the body to the action of an external factor. The first, initial, provides imperfect adaptation. It starts from the moment of action of the stimulus and is carried out on the basis of existing functional mechanisms (for example, increased heat production during cooling).
6 . Activeadaptation
Formation of protective mechanisms, while prerequisite survival is the induction of the synthesis of enzymes with new properties or new proteins that provide cell protection and metabolism in previously unsuitable conditions for life. The end result of this adaptation is to expand the ecological boundaries of plant life.
7 . Passiveadaptation
- "leaving" from the damaging effect of the stressor or coexistence with it. This type of adaptation is of great importance for plants, because, unlike animals, they are not able to escape or hide from the action of a harmful factor. Passive adaptations include, for example, the transition to a dormant state, the ability of plants to isolate "aggressive" compounds such as heavy metals in aging organs, tissues or vacuoles, i.e. coexist with them. The real “escape” from the acting factor is the very short ontogeny of ephemeral plants, which allows them to form seeds before the onset of unfavorable conditions. So, for example, in response to an increase in air temperature, the plant “leaves” the active factor, lowering the temperature of tissues due to transpiration, and at the same time actively protects cellular metabolism from high temperature by synthesizing heat shock proteins.
In the process of adaptation, the plant goes through two different stages:
1) fast initial response;
2) a much longer stage associated with the formation of new isoenzymes or stress proteins that ensure the flow of metabolism under changed conditions.
The rapid initial response of a plant to a damaging effect is called a stress response, and the phase following it is called a specialized adaptation. When the stressor ceases, the plant enters a state of recovery.
8 . ClassificationplantsVdependenciesfromtheirtemperatureoptimum
According to the degree of adaptation of plants to conditions of extreme heat deficiency, three groups can be distinguished:
1) non-cold-resistant plants - are severely damaged or die at temperatures that have not yet reached the freezing point of water. Death is associated with inactivation of enzymes, impaired metabolism of nucleic acids and proteins, membrane permeability, and cessation of the flow of assimilates. These are plants of tropical rainforests, algae of warm seas;
2) non-frost-resistant plants - tolerate low temperatures, but die as soon as ice begins to form in the tissues. With the onset of the cold season, they increase the concentration of osmotically active substances in the cell sap and cytoplasm, which lowers the freezing point to - (5-7) ° C. The water in the cells can cool below freezing without immediate ice formation. The supercooled state is unstable and lasts most often for several hours, which, however, allows plants to endure frosts. These are some evergreen subtropical plants - laurels, lemons, etc.;
3) ice-resistant, or frost-resistant, plants - grow in areas with a seasonal climate, with cold winters. During severe frosts, the above-ground organs of trees and shrubs freeze through, but nevertheless remain viable, since in the cells crystal ice is not formed. Plants are prepared for the transfer of frost gradually, undergoing preliminary hardening after the growth processes are completed. Hardening consists in the accumulation in cells of sugars (up to 20-30%), derivatives of carbohydrates, some amino acids and other protective substances that bind water. At the same time, the frost resistance of the cells increases, since the bound water is more difficult to be drawn off by the ice crystals formed in the extracellular spaces.
Thaws in the middle, and especially at the end of winter, cause a rapid decrease in plant resistance to frost. After the end of winter dormancy, hardening is lost. Spring frosts, which come suddenly, can damage shoots that have begun to grow, and especially flowers, even in frost-resistant plants.
According to the degree of adaptation to high temperatures, the following groups of plants can be distinguished:
1) non-heat-resistant plants are damaged already at + (30-40) ° С (eukaryotic algae, aquatic flowering, terrestrial mesophytes);
2) heat-tolerant plants tolerate half an hour heating up to + (50-60) ° С (plants of dry habitats with strong insolation - steppes, deserts, savannas, dry subtropics, etc.).
Some plants are regularly affected by fires, when the temperature briefly rises to hundreds of degrees. Fires are especially frequent in savannahs, in dry hardwood forests and shrubs such as chaparral. There is a group of pyrophyte plants that are resistant to fires. Savannah trees have a thick bark on their trunks, impregnated with refractory substances that reliably protect internal tissues. The fruits and seeds of pyrophytes have thick, often lignified integuments that crack when scorched by fire.
9 . Heat resistanceplants
Heat resistance (heat tolerance) - the ability of plants to endure the action of high temperatures, overheating. This is a genetically determined trait. According to heat resistance, three groups of plants are distinguished.
Heat-resistant - thermophilic blue-green algae and bacteria of hot mineral springs, capable of tolerating temperatures up to 75-100 ° C. The heat resistance of thermophilic microorganisms is determined high level metabolism, high content RNA in cells, cytoplasmic protein resistance to thermal coagulation.
Heat-tolerant - plants of deserts and dry habitats (succulents, some cacti, members of the Crassula family), withstanding heating by sunlight up to 50-65 ° C. The heat resistance of succulents is largely determined by the increased viscosity of the cytoplasm and the content of bound water in the cells, and reduced metabolism.
Non-heat-resistant - mesophytic and aquatic plants. Mesophytes of open places endure short-term exposure to temperatures of 40-47°C, shaded places - about 40-42°C, aquatic plants withstand temperatures up to 38-42°C. Of the agricultural crops, heat-loving plants of southern latitudes (sorghum, rice, cotton, castor beans, etc.) are the most heat-tolerant.
Many mesophytes tolerate high air temperatures and avoid overheating due to intensive transpiration, which reduces the temperature of the leaves. More heat-resistant mesophytes are distinguished by increased viscosity of the cytoplasm and increased synthesis of heat-resistant enzyme proteins.
Heat resistance largely depends on the duration of high temperatures and their absolute value. Most agricultural plants begin to suffer when the temperature rises to 35-40°C. At these and higher temperatures, the normal physiological functions of the plant are inhibited, and at a temperature of about 50 ° C, protoplasm coagulation and cell death occur.
Exceeding the optimal temperature level leads to partial or global denaturation of proteins. This causes the destruction of the protein-lipid complexes of the plasma membrane and other cell membranes, leading to the loss of the osmotic properties of the cell.
Under the action of high temperatures in plant cells, the synthesis of stress proteins (heat shock proteins) is induced. Plants in dry, light habitats are more resistant to heat than shade-loving ones.
Heat resistance is largely determined by the phase of growth and development of plants. High temperatures cause the greatest harm to plants in the early stages of their development, since young, actively growing tissues are less stable than old and “resting” ones. Resistance to heat in various plant organs is not the same: underground organs are less resistant, shoots and buds are more resistant.
10 . Physiological and biochemicalbasicsnon-specificAndspecificreactionsonstress
Nonspecific are the same type of reactions of the body to the action of heterogeneous stressors or different organisms to the same stress factor. Specific reactions include responses that differ qualitatively depending on the factor and genotype.
The primary nonspecific processes occurring in plant cells under the action of any stressors include the following:
1. Increased membrane permeability, depolarization of the membrane potential of the plasmalemma.
2. Entry of calcium ions into the cytoplasm from cell walls and intracellular compartments (vacuole, endoplasmic reticulum, mitochondria).
3. Shift in the pH of the cytoplasm to the acid side.
4. Activation of the assembly of actin microfilaments of the cytoskeleton, resulting in an increase in the viscosity and light scattering of the cytoplasm.
5. Increased oxygen uptake, accelerated consumption of ATP, development of free radical processes.
6. An increase in the content of the amino acid proline, which can form aggregates that behave like hydrophilic colloids and help retain water in the cell. Proline can bind to protein molecules, protecting them from denaturation.
7. Activation of the synthesis of stress proteins.
8. Increased activity of the proton pump in the plasmalemma and, possibly, in the tonoplast, which prevents adverse shifts in ion homeostasis.
9. Strengthening the synthesis of ethylene and abscisic acid, inhibition of division and growth, absorption activity of cells and other physiological processes occurring under normal conditions.
11 . Showgeneticsubsequencereactionsonstress
The concept of specificity and nonspecificity of adaptive reactions is used, firstly, by determining the attitude of an organism (species, variety) to various stressors, and secondly, by characterizing the reaction of various organisms (species, varieties) to the same stressor. The most important nonspecific response of cells to the action of stressors is the synthesis of specific proteins. Protein-coding genes have been identified and it has been shown that stress induces the expression of a number of genes. This makes it possible to judge which genes are responsible for resistance. Stress proteins are synthesized in plants in response to various influences: anaerobiosis, high and low temperatures, dehydration, high salt concentrations, the action of heavy metals, pests, as well as wound effects and ultraviolet radiation. Stress proteins are diverse and form groups of high and low molecular weight proteins. Proteins with the same molecular weight represented by different polypeptides. This is due to the fact that each group of proteins is encoded not by one gene, but by a family of related genes. After completion of protein synthesis, various modifications can occur, such as reversible phosphorylation. The protective role of stress proteins in a plant is confirmed by the facts of cell death upon the introduction of inhibitors of protein synthesis during the period of stressor action. On the other hand, changes in the structure of the gene, damaging the synthesis of proteins, lead to a loss of cell resistance. As a result of a change in the action of a factor or factors, the cell life switches to a stress program. This is carried out simultaneously at many levels of regulation. The expression of genes whose activity is characteristic of cell life under normal conditions is inhibited, and stress response genes are activated. Activation of stress genes occurs due to the reception of the signal and the corresponding signal chain. Abiotic stress factors (excess salts, elevated temperature, etc.) seem to activate receptors in the plasma membrane. There, a signal chain begins, which through various intermediates, such as protein kinases, phosphatases, leads to the formation of a transcription factor. These factors in the nucleus activate genes by binding to specific promoters. The sequence of reactions is as follows: stress signal -> receptor in the plasma membrane -> signal chain in the cytosol -> transcription factor in the nucleus -> stress-induced gene promoter -> mRNA -> protein -> protective role in the plant.
12 . Whatsuchcross-adaptation?
Cross or cross - adaptations are adaptations in which the development of resistance to one factor increases resistance to a concomitant one.
13 . ClassificationplantsByrelationTolight.Examples
In relation to light, all plants, including forest trees, are divided into the following ecological groups:
heliophytes (light-loving), requiring a lot of light and able to tolerate only slight shading (photophilous include almost all cacti and other succulents, many representatives of tropical origin, some subtropical shrubs) pine, wheat, larch (powerful cuticle, many stomata);
sciophytes (shade-loving) - on the contrary, they are content with insignificant lighting and can exist in the shade (various conifers, many ferns, some decorative leafy plants belong to shade-tolerant ones);
shade-tolerant (facultative heliophytes).
Heliophytes. light plants. Inhabitants of open habitats: meadows, steppes, upper tiers of forests, early spring plants, many cultivated plants.
small size of leaves; seasonal dimorphism occurs: leaves are small in spring, larger in summer;
leaves are located at a large angle, sometimes almost vertically;
leaf blade shiny or densely pubescent;
form scattered stands.
Sciophytes. Can't stand strong light. Habitat: lower darkened layers; inhabitants of the deep layers of water bodies. First of all, these are plants growing under the canopy of the forest (oxalis, kostyn, gout).
They are characterized by the following features:
leaves are large, tender;
dark green leaves;
leaves are mobile;
the so-called leaf mosaic is characteristic (that is, a special arrangement of leaves, in which the leaves do not obscure each other as much as possible).
Shade-tolerant. They occupy an intermediate position. They often thrive in normal lighting conditions, but can also tolerate dark conditions. According to their characteristics, they occupy an intermediate position.
The reasons for this difference must be sought, first of all, in the specific features of chlorophyll, then in the different architectonics of the species (in the structure of the shoots, the arrangement and shape of the leaves). By arranging the trees of the forest according to their need for light, which is manifested in their competition when they grow together, and putting the most light-loving in front, we will get approximately the following rows.
1) Larch, birch, aspen, alder
2) ash, oak, elm
3) spruce, linden, hornbeam, beech, fir.
It is a remarkable and biologically important circumstance that almost all trees can tolerate more shading when young than when they are more mature. Further, it should be noted that the ability to tolerate shading is in a certain dependence on the fertility of the soil.
Plants are divided into:
1. long-day 16-20 hours day length - temperate zone, northern latitude,
2. short-day night is equal to day - equatorial latitudes,
3. neutral - American maple, medicinal dandelion, etc.
14 . Peculiaritiesshade-tolerantplantsAndtheircharacteristic
Shade-tolerant plants, plants (mainly woody, many herbaceous under the canopy of hardwoods, greenhouses, etc.), which tolerate some shading, but develop well in direct sunlight. Physiologically, T. r. characterized by a relatively low intensity of photosynthesis. Leaves T. r. have a number of anatomical and morphological features: the columnar and spongy parenchyma are poorly differentiated, the cells contain a small number (10–40) of chloroplasts, the surface area of which varies between 2–6 cm2 per 1 cm2 of leaf area. A number of plants under the forest canopy (for example, hoof, gout, etc.) in early spring, before the leaves of the tree layer open, are physiologically photophilous, and in summer, with a closed canopy, they are shade-tolerant.
Shade-tolerant plants - plants that are tolerant of shading, growing mainly in shady habitats (unlike light-loving plants, heliophytes), but also developing well in open areas with more or less direct sunlight (unlike shade-loving plants, sciophytes) . Shade-tolerant plants are considered in plant ecology as an intermediate group between heliophytes and sciophytes; they are defined as facultative heliophytes.
Features of the morphology and physiology of shade-tolerant plants
The mosaic arrangement of the leaves contributes to a better capture of diffused light. sugar maple leaves
Shade-tolerant plants are characterized by a relatively low intensity of photosynthesis. Their leaves differ from the leaves of heliophytes in a number of important anatomical and morphological features. In the leaf of shade-tolerant plants, columnar and spongy parenchyma are usually poorly differentiated; characterized by enlarged intercellular spaces. The epidermis is rather thin, single-layered, the cells of the epidermis may contain chloroplasts (which is never found in heliophytes). The cuticle is usually thin. Stomata are usually located on both sides of the leaf with an insignificant predominance on the reverse side (in photophilous plants, as a rule, stomata are absent on the front side or are located mainly on the reverse side). Compared with heliophytes, shade-tolerant plants have a significantly lower content of chloroplasts in leaf cells - on average, from 10 to 40 per cell; the total surface of leaf chloroplasts slightly exceeds its area (2-6 times; while in heliophytes, the excess is tens of times).
Some shade-tolerant plants are characterized by the formation of anthocyanin in the cells when growing in bright sun, which gives a reddish or brownish color to the leaves and stems, which is uncharacteristic in the natural habitat. In others, when growing in direct sunlight, a paler color of the leaves is noted.
The appearance of shade-tolerant plants also differs from light-loving ones. Shade-tolerant plants usually have wider, thinner, softer leaves to capture more diffused sunlight. In shape, they are usually flat and smooth (whereas heliophytes often have folded, tubercular leaves). The horizontal arrangement of foliage is characteristic (in heliophytes, leaves are often located at an angle to the light) and leaf mosaic. Forest grasses are usually elongated, tall, have an elongated stem.
Many shade-tolerant plants have a high plasticity of their anatomical structure, depending on the illumination (first of all, this concerns the structure of the leaves). For example, in beech, lilac, and oak, leaves formed in the shade usually have significant anatomical differences from leaves grown in bright sunlight.
Some root crops (radishes, turnips) and spicy plants (parsley, lemon balm, mint) are shade-tolerant. Regarding shade-tolerant common cherry (one of the few shade-tolerant fruit trees); some berry bushes are shade-tolerant (currants, blackberries, some varieties of gooseberries) and herbaceous plants(garden strawberries, lingonberries).
Some shade-tolerant plants are valuable fodder crops. Vetch grown for these purposes is also used as green manure.
15. Light-lovingplantsAndtheiranatomical and physiologicalpeculiarities
Light-loving plants, heliophytes, plants growing in open places and not enduring long-term shading; For normal growth, they need intense solar or artificial radiation. Mature plants are more photophilous than young ones. K S. r. include both herbaceous (large plantain, water lily, etc.) and woody (larch, acacia, etc.) plants, early spring - steppes and semi-deserts, and from cultivated - corn, sorghum, sugar cane, etc. . have a number of anatomical, morphological and physiological features: relatively thick leaves with small-celled columnar and spongy parenchyma and a large number of stomata. Leaf cells contain from 50 to 300 small chloroplasts, the surface of which is tens of times greater than the surface of the leaf. Compared with shade-tolerant plants, the leaves of S. r. contain more chlorophyll per unit area and less - per unit mass of the leaf. A characteristic physiological sign of S. p. - high intensity of photosynthesis, (heliophytes).
Plants that do not tolerate long-term shading. These are plants of open habitats: steppe and meadow grasses, rock lichens, plants of alpine meadows, coastal and aquatic (with floating leaves), early spring herbaceous plants of deciduous forests.
Light-loving trees include: saxaul, honey locust, black locust, albizia, birch, larch, Atlas and Lebanese cedars, Scots pine, common ash, Japanese sophora, white mulberry, squat elm, Amur velvet, walnut, black and white poplar, aspen , common oak; to shrubs - narrow-leaved sucker, amorpha, oleander, etc. Leafy, golden, white-variegated forms of tree species and shrubs are more demanding of light. In light-loving plants, the leaves are usually smaller than in shade-tolerant ones. Their leaf blade is located vertically or at a large angle to the horizontal plane, so that during the day the leaves receive only gliding rays. This arrangement of leaves is typical for eucalyptus, mimosa, acacia, and many steppe herbaceous species. The surface of the leaf is shiny (laurel, magnolia), covered with a light wax coating (cacti, spurge, crassula) or densely pubescent, there is a thick cuticle. The internal structure of the leaf is distinguished by its features: the palisade parenchyma is well developed not only on the upper, but also on the lower side of the leaf, the mesophyll cells are small, without large intercellular spaces, the stomata are small and numerous. photophilous plants. characterized by a high intensity of photosynthesis, slowing down growth processes, more sensitive to the lack of light. Demanding for light changes with the age of the plant and depends on environmental conditions. The same species is more shade tolerant when young. When moving (in culture) a tree species from warm regions to colder regions, its need for light increases, which is also affected by the nutritional conditions of plants. On fertile soil plants can thrive with less intense light, on poor soil the need for light increases.
16. Shade-lovingplantsAndtheiranatomical and physiologicalpeculiarities
Plants that can't stand strong light. These include, for example, many forest herbs (oxalis, maynik, etc.). When felling the forest, once in the light, they show signs of oppression and die. The highest intensity of photosynthesis is observed in such plants under moderate lighting.
17. InfluencetemperatureonheightAnddevelopmentplants.Classificationplants
Most agricultural plants begin to suffer when the temperature rises to 35--40°C. At these and higher temperatures, the normal physiological functions of the plant are inhibited, and at a temperature of about 50 ° C, protoplasm coagulation and cell death occur. Exceeding the optimal temperature level leads to partial or global denaturation of proteins. This causes the destruction of the protein-lipid complexes of the plasma membrane and other cell membranes, leading to the loss of the osmotic properties of the cell. As a result, there is a disorganization of many cell functions, a decrease in the rate of various physiological processes. So, at a temperature of 20°C, all cells undergo the process of mitotic division, at 38°C, mitosis is observed in every seventh cell, and an increase in temperature to 42°C reduces the number of dividing cells by 500 times (one dividing cell per 513 non-dividing cells). At maximum temperatures, the consumption of organic substances for respiration exceeds its synthesis, the plant becomes poorer in carbohydrates, and then begins to starve. This is especially pronounced in plants of a more temperate climate (wheat, potatoes, many garden crops).
Photosynthesis is more sensitive to high temperatures than respiration. At suboptimal temperatures, plants stop growing and photoassimilating, which is due to a violation of the activity of enzymes, an increase in respiratory gas exchange, a decrease in its energy efficiency, an increase in the hydrolysis of polymers, in particular protein, and poisoning of the protoplasm with decay products harmful to the plant (ammonia, etc.). In heat-resistant plants, under these conditions, the content of organic acids that bind excess ammonia increases.
Enhanced transpiration provided by a powerful root system can serve as a way to protect against overheating. As a result of transpiration, the temperature of plants sometimes decreases by 10–15°C. Withering plants, with closed stomata, die more easily from overheating than adequately supplied with water. Plants tolerate dry heat more easily than humid heat, since during heat with high air humidity, the regulation of leaf temperature due to transpiration is limited.
An increase in temperature is especially dangerous with strong insolation. To reduce the intensity of exposure to sunlight, plants arrange their leaves vertically, parallel to its rays (erectoid). At the same time, chloroplasts actively move in the cells of the leaf mesophyll, as if moving away from excessive insolation. Plants have developed a system of morphological and physiological adaptations that protect them from thermal damage: a light surface color that reflects insolation; folding and twisting of leaves; pubescence or scales that protect deeper tissues from overheating; thin layers of cork tissue that protect the phloem and cambium; greater thickness of the cuticular layer; a high content of carbohydrates and a low content of water in the cytoplasm, etc. Under field conditions, the combined effect of high temperatures and dehydration is especially detrimental. With prolonged and deep wilting, not only photosynthesis is inhibited, but also respiration, which causes a violation of all the basic physiological functions of the plant. High temperatures cause the greatest harm to plants in the early stages of their development, since young, actively growing tissues are less stable than old and “resting” ones. Heat resistance in various plant organs is not the same: underground organs are less stable, shoots and buds are more. Plants react very quickly to heat stress by inductive adaptation. During the formation of generative organs, the heat resistance of annual and biennial plants decreases. The harmful effect of elevated temperatures is one of the most important reasons for the significant reduction in yields of early spring crops when their sowing is delayed. For example, in wheat in the tillering phase, spikelet differentiation occurs in the growth cone. High temperature of the soil and air leads to damage to the growth cone, speeds up the process and reduces the time for passing IV-V stages, as a result, the number of spikelets per spike, as well as the number of flowers per spike, decreases, which leads to a decrease in yield.
The development of plants, their growth and other physiological processes take place under certain temperature conditions. Moreover, each type of plant has temperature minima, optima and maxima for each physiological process. Therefore, heat is an important ecological factor that determines the life of an individual plant, the distribution of plant species over the earth's surface, and the formation of vegetation types.
For each plant species, two temperature limits must be distinguished: minimum and maximum, i.e., temperatures at which life processes in plants cease, and the optimum temperature, which is most favorable for plant life. For various physiological processes (photosynthesis, respiration, growth) in the same plant species, the position of these boundaries is not the same. It is also different for phenological phases in tree species. For example, the growth of spruce and fir shoots begins at temperatures from +7 to +10°C, and flowering begins at higher temperatures, above +10°C. Such species as alder, aspen, hazel, willow bloom at lower temperatures, and their shoot growth occurs much later at higher temperatures.
For all life processes of plants, it is characteristic that the optimal temperatures for them are closer to the maximum than to the minimum. If the growth of pine occurs within the temperature range from +7 to +34°, then the optimum temperature is from +25 to +28°.
Seeds of many plants, including woody ones, require preliminary exposure to low temperatures for timely normal germination. The stratification of seeds of some woody plants is based on this principle: ash, linden, euonymus, hawthorn. Also, after the action of low temperatures, the blooming of leaf and flower buds in woody plants occurs faster.
Higher temperatures are better tolerated by plants if they contain little water (especially plant seeds and spores) or if they are dormant (desert plants).
Protection against overheating of plants is transpiration, which significantly lowers the body temperature of the plant. The accumulation of salts in plant cells also increases the resistance of their protoplasm to coagulation under the action of high temperature. This is especially common in desert plants (saxaul, saltwort). In sprouts and annual seedlings of woody plants, high temperature, in addition to drying, sometimes causes opal of the root neck.
The minimum temperature has a large amplitude for various plant species. So, some tropical plants are damaged by cold already at a temperature of + 5 °, and die below zero (for example, some orchids). The reason for the death of plants from the cold is mainly the loss of water by the cells. Ice crystals formed in the intercellular spaces draw water out of the cells, drying them out and destroying them. Therefore, plants and their parts that contain little water are more tolerant of low temperatures (for example, lichens, dry seeds and plant spores).
In many cases, it is not the low temperature itself, which leads to freezing, that is harmful to the plant, but rapid thawing or alternating thawing with freezing. However, some plants, such as sphagnum mosses, although they contain a lot of water, can freeze and thaw quickly without harm to life.
Very low winter temperatures (-40 - 45 °) are tolerated by some tree species without harm (pine, larch, Siberian cedar, birch, aspen), other species are damaged. However, the nature and extent of damage are different. In European spruce, one-year-old needles and even resting buds are partially or completely damaged. In oak, ash, maple, dormant buds die off; in this case, the trees remain without leaves for a long time, until the end of June, until the dormant buds germinate and restore normal crown leafing. Sometimes the resting buds remain intact, but the cambium of the trunk and branches is very badly damaged by frost, which is especially dangerous, because after that the buds open in the spring, but soon the young shoots wither and the tree dies off completely. This is observed in some poplars, young trees of black alder, apple trees.
When the outer parts of the trunk are supercooled during sharp drops in temperature in winter, sometimes a longitudinal rupture of the trunk surface occurs and frost cracks form, which weakens the tree and spoils the quality of the wood. Coniferous trees sometimes they suffer from early spring heating, when the thawed needles begin to evaporate water, and water does not yet flow from the frozen parts of the trunk and roots. This phenomenon is called sunburn, it leads to browning of younger, usually one-year-old needles.
Trees react differently to late spring frosts, which occur at the beginning of the growing season, when the temperature in the lower layers of the atmosphere (up to a height of 3–4 m) drops to -3–5 ° at night. Then, in young trees, shoots that have just appeared after bud break are damaged to such an extent that sometimes they die completely; such species include spruce, fir, oak, ash.
In relation to heat, woody plants naturally growing or bred in the USSR are classified as follows:
1. Completely cold-resistant, completely undamaged by low winter temperatures, enduring frosts down to -45-50 °, and some even lower, not damaged by late spring frosts. Such woody plants include Siberian and Dahurian larches, Scotch pine, Siberian spruce, Siberian and dwarf cedars, common juniper, aspen, downy and warty birch, gray alder, mountain ash, goat willow, fragrant poplar.
2. Cold-resistant, enduring severe winters, but damaged by very severe frosts (below - 40 °). In some, the needles are damaged, in others, resting buds. Some species of this group are damaged by late spring frosts. These include European spruce, Siberian fir, black alder, small-leaved linden, elm, elm, Norway maple, black and white poplars.
3. Relatively thermophilic with a longer growing season, as a result of which their annual shoots do not always have time to become woody and are partially or completely beaten by frost; all plants are severely damaged by very low winter temperatures; many of them are damaged by late spring frosts. Such species include summer and winter oaks, common ash, large-leaved linden, hornbeam, birch bark, velvet tree, Manchurian walnut, euonymus, Canadian poplar.
4. Heat-loving with an even longer growing season, their shoots often do not ripen and die from frost. In severe prolonged frosts in such plants, the completely aerial part dies, and its renewal occurs from dormant buds at the root neck. Such species include pyramidal poplar, walnut, real chestnut, mulberry, white acacia.
5. Very heat-loving, which do not tolerate or do not tolerate prolonged frosts down to -10-15 °. At this temperature for several days they either die completely or are badly damaged; these include real cedar, cypress, eucalyptus, citrus fruits, cork oak, large-flowered magnolia, silk acacia.
A sharp boundary between these groups cannot be drawn; many woody plants occupy an intermediate position. The increase in cold resistance of the same species also depends on the growing conditions. However, all this does not exclude the need for a comparative characterization and classification of woody plants in relation to heat.
18. Cold resistanceatplants
Ecological groups of plants: hydatophytes, hydrophytes, hygrophytes, mesophytes and xerophytes. General characteristics of ultraviolet radiation and its role in the evolution of living things. Influence of UV radiation on the content of photosynthetic pigments. The concept of plant stress.
term paper, added 11/07/2015
Consideration and analysis of the main groups of factors that can cause stress in plants. Acquaintance with the phases of the Selye triad in the development of stress in plants. Investigation and characterization of the physiology of plant stress resistance using defense systems.
test, added 04/17/2019
Stress as a set of non-specific adaptive reactions of the body to the impact of adverse factors. oxidative stress. Psychological reactions of the population living in radioactively contaminated territories to the radiation threat.
presentation, added 05/03/2017
Activation of certain enzymatic systems of plants with the help of trace elements. The role of soil as a complex edaphic factor in plant life, the ratio of trace elements. Classification of plants depending on the need for nutrients.
term paper, added 04/13/2012
Definition of the concepts "drought" and "drought resistance". Examine the response of plants to drought. The study of plant types in relation to the water regime: xerophytes, hygrophytes and mesophytes. Description of the mechanism of adaptation of plants to environmental conditions.
abstract, added 05/07/2015
The essence of the concept of "photoperiodism". Neutral, long-day, short-day plants. Light and its role in plant life. Ecological groups of plants in relation to light. Plant adaptation to light regime. Localization of photoperiodic reactions.
term paper, added 05/20/2011
Characteristics of the main groups of plants in relation to water. Anatomical and morphological adaptations of plants to the water regime. Physiological adaptations of plants confined to habitats of different moisture content.
term paper, added 03/01/2002
Taxonomic units of the plant world, plant systematics, their importance in the nutrition of wild animals and humans. The structure and functions of the leaf epidermis; classification, biological significance of the kidneys. Ecological groups of plants in relation to soil composition.
control work, added 02/06/2012
Effect of light on nutrition and evaporation. The importance of light for the distribution of plants. The strength of the light and the direction of the light rays. Classification of plants in relation to light. Leaf direction and lighting. Differences in the anatomical structure.
abstract, added 01/21/2003
Cardinal temperature points. The process of photosynthesis with the help of light. circadian cycles. Growth movements: typification, possible mechanisms. Plant adaptations to temperatures. Neoplasm of specific proteins resistant to dehydration.
The adaptability of plant ontogenesis to environmental conditions is the result of their evolutionary development (variability, heredity, selection). During the phylogenesis of each plant species, in the process of evolution, certain needs of the individual for the conditions of existence and adaptability to the ecological niche he occupies have been developed. Moisture and shade tolerance, heat resistance, cold resistance and other ecological features of specific plant species have been formed in the course of evolution as a result of long-term exposure to appropriate conditions. So, heat-loving plants and plants of a short day are characteristic of the southern latitudes, less demanding for heat and plants of a long day - for the northern ones.
In nature, in one geographical region, each plant species occupies an ecological niche corresponding to its biological characteristics: moisture-loving - closer to water bodies, shade-tolerant - under the forest canopy, etc. The heredity of plants is formed under the influence of certain environmental conditions. The external conditions of plant ontogenesis are also important.
In most cases, plants and crops (plantings) of agricultural crops, experiencing the action of certain adverse factors, show resistance to them as a result of adaptation to the conditions of existence that have developed historically, which was noted by K. A. Timiryazev.
1. Basic living environments.
When studying the environment (the habitat of plants and animals and human production activities), the following main components are distinguished: the air environment; aquatic environment (hydrosphere); fauna (human, domestic and wild animals, including fish and birds); flora (cultivated and wild plants, including those growing in water); soil (vegetation layer); subsoil (upper part of the earth's crust, within which mining is possible); climatic and acoustic environment.
The air environment can be external, in which most people spend a smaller part of their time (up to 10-15%), internal production (a person spends up to 25-30% of their time in it) and internal residential, where people stay most of the time (up to 60 -70% or more).
Outside air at the earth's surface contains by volume: 78.08% nitrogen; 20.95% oxygen; 0.94% inert gases and 0.03% carbon dioxide. At an altitude of 5 km, the oxygen content remains the same, while nitrogen increases to 78.89%. Often the air near the surface of the earth has various impurities, especially in cities: there it contains more than 40 ingredients that are alien to the natural air environment. Indoor air in dwellings, as a rule, has
elevated levels of carbon dioxide, and indoor air industrial premises usually contains impurities, the nature of which is determined by the production technology. Among the gases, water vapor is released, which enters the atmosphere as a result of evaporation from the Earth. Most of it (90%) is concentrated in the lowest five-kilometer layer of the atmosphere, with height its amount decreases very quickly. The atmosphere contains a lot of dust that gets there from the surface of the Earth and partly from space. During strong waves, the winds pick up water spray from the seas and oceans. This is how salt particles get into the atmosphere from the water. As a result of volcanic eruptions, forest fires, industrial facilities, etc. air is polluted by products of incomplete combustion. Most of all dust and other impurities are in the ground layer of air. Even after rain, 1 cm contains about 30 thousand dust particles, and in dry weather there are several times more of them in dry weather.
All these tiny impurities affect the color of the sky. Molecules of gases scatter the short-wavelength part of the spectrum of the sun's beam, i.e. purple and blue rays. So during the day the sky is blue. And impurity particles, which are much larger than gas molecules, scatter light rays of almost all wavelengths. Therefore, when the air is dusty or contains water droplets, the sky becomes whitish. At high altitudes, the sky is dark purple and even black.
As a result of the photosynthesis taking place on Earth, vegetation annually forms 100 billion tons of organic substances (about half is accounted for by the seas and oceans), assimilating about 200 billion tons of carbon dioxide and releasing about 145 billion tons into the environment. free oxygen, it is believed that due to photosynthesis, all the oxygen in the atmosphere is formed. The role of green spaces in this cycle is indicated by the following data: 1 hectare of green spaces, on average, purifies the air from 8 kg of carbon dioxide per hour (200 people emitted during this time when breathing). An adult tree releases 180 liters of oxygen per day, and in five months (from May to September) it absorbs about 44 kg of carbon dioxide.
The amount of oxygen released and carbon dioxide absorbed depends on the age of green spaces, species composition, planting density and other factors.
Equally important are marine plants - phytoplankton (mainly algae and bacteria), which release oxygen through photosynthesis.
The aquatic environment includes surface and ground waters. surface water mainly concentrated in the ocean, containing 1 billion 375 million cubic kilometers - about 98% of all water on Earth. The surface of the ocean (water area) is 361 million square kilometers. It is about 2.4 times the land area - a territory that occupies 149 million square kilometers. The water in the ocean is salty, and most of it (more than 1 billion cubic kilometers) retains a constant salinity of about 3.5% and a temperature of about 3.7 ° C. Noticeable differences in salinity and temperature are observed almost exclusively in the surface layer of water, and also in the outskirts and especially in mediterranean seas. The content of dissolved oxygen in water decreases significantly at a depth of 50-60 meters.
Groundwater can be saline, brackish (lower salinity) and fresh; existing geothermal waters have an elevated temperature (more than 30ºC).
For the production activities of mankind and its household needs, fresh water is required, the amount of which is only 2.7% of the total volume of water on Earth, and a very small share of it (only 0.36%) is available in places that are easily accessible for extraction. Most of fresh water found in snows and freshwater icebergs found in areas mainly of the Antarctic Circle.
The annual global river runoff of fresh water is 37.3 thousand cubic kilometers. In addition, a part of groundwater equal to 13 thousand cubic kilometers can be used. Unfortunately, most of the river flow in Russia, amounting to about 5,000 cubic kilometers, falls on the marginal and sparsely populated northern territories.
The climatic environment is an important factor, which determines the development of various species of the animal and plant world and its fertility. characteristic feature Russia is that most of its territory has a much colder climate than in other countries.
All considered components of the environment are included in
BIOSPHERE: the shell of the Earth, including part of the atmosphere, hydrosphere and upper part lithospheres, which are interconnected by complex biochemical cycles of matter and energy migration, the geological shell of the Earth inhabited by living organisms. The upper limit of the life of the biosphere is limited by the intense concentration of ultraviolet rays; lower - high temperature of the earth's interior (over 100`C). Its extreme limits are reached only by lower organisms - bacteria.
Adaptation (adaptation) of a plant to specific environmental conditions is provided by physiological mechanisms (physiological adaptation), and in a population of organisms (species) - due to the mechanisms of genetic variability, heredity and selection (genetic adaptation). Environmental factors can change regularly and randomly. Regularly changing environmental conditions (change of seasons) develop in plants genetic adaptation to these conditions.
In the natural conditions of growth or cultivation of a species, in the course of their growth and development, they are often affected by adverse environmental factors, which include temperature fluctuations, drought, excessive moisture, soil salinity, etc. Each plant has the ability to adapt to changing conditions. environmental conditions within the limits determined by its genotype. The higher the ability of a plant to change metabolism in accordance with the environment, the wider the reaction rate of this plant and the better the ability to adapt. This property distinguishes resistant varieties of agricultural crops. As a rule, slight and short-term changes in environmental factors do not lead to significant disturbances in the physiological functions of plants, which is due to their ability to maintain a relatively stable state under changing environmental conditions, i.e., to maintain homeostasis. However, sharp and prolonged impacts lead to disruption of many functions of the plant, and often to its death.
Under the influence of unfavorable conditions, the decrease in physiological processes and functions can reach critical levels that do not ensure the implementation of the genetic program of ontogenesis, energy metabolism, regulatory systems, protein metabolism and other vital functions of the plant organism are disrupted. When a plant is exposed to unfavorable factors (stressors), a stressed state arises in it, a deviation from the norm - stress. Stress is a general non-specific adaptive reaction of the body to the action of any adverse factors. There are three main groups of factors that cause stress in plants: physical - insufficient or excessive humidity, light, temperature, radioactive radiation, mechanical stress; chemical - salts, gases, xenobiotics (herbicides, insecticides, fungicides, industrial waste, etc.); biological - damage by pathogens or pests, competition with other plants, the influence of animals, flowering, fruit ripening.
The strength of stress depends on the rate of development of an unfavorable situation for the plant and the level of the stress factor. With the slow development of unfavorable conditions, the plant adapts better to them than with a short-term but strong effect. In the first case, as a rule, specific mechanisms of resistance are manifested to a greater extent, in the second - non-specific ones.
Under unfavorable natural conditions, the resistance and productivity of plants are determined by a number of signs, properties, and protective and adaptive reactions. Various plant species provide stability and survival in adverse conditions in three main ways: through mechanisms that allow them to avoid adverse effects (dormancy, ephemera, etc.); through special structural devices; due to physiological properties that allow them to overcome the harmful effects of the environment.
Annual agricultural plants in temperate zones, completing their ontogeny in relatively favorable conditions, overwinter in the form of stable seeds (dormancy). Many perennial plants overwinter as underground storage organs (bulbs or rhizomes) protected from freezing by a layer of soil and snow. Fruit trees and shrubs of temperate zones, protecting themselves from the winter cold, shed their leaves.
Protection from adverse environmental factors in plants is provided by structural adaptations, features of the anatomical structure (cuticle, crust, mechanical tissues, etc.), special protective organs (burning hairs, spines), motor and physiological reactions, and the production of protective substances (resins, phytoncides , toxins, protective proteins).
Structural adaptations include small-leaved and even the absence of leaves, a waxy cuticle on the surface of leaves, their dense omission and immersion of stomata, the presence of succulent leaves and stems that retain water reserves, erectoid or drooping leaves, etc. Plants have various physiological mechanisms that allow them to adapt to unfavorable conditions. environmental conditions. This is a self-type of photosynthesis in succulent plants, minimizing water loss and essential for the survival of plants in the desert, etc.
2. Adaptation in plants
Plant resistance to low temperatures is divided into cold resistance and frost resistance. Cold resistance is understood as the ability of plants to tolerate positive temperatures slightly higher than 0 C. Cold resistance is characteristic of plants of the temperate zone (barley, oats, flax, vetch, etc.). Tropical and subtropical plants are damaged and die at temperatures from 0º to 10º C (coffee, cotton, cucumber, etc.). For the majority of agricultural plants, low positive temperatures are not harmful. This is due to the fact that during cooling, the enzymatic apparatus of plants is not upset, resistance to fungal diseases does not decrease, and no noticeable damage to plants occurs at all.
The degree of cold resistance of different plants is not the same. Many plants of southern latitudes are damaged by cold. At a temperature of 3 ° C, cucumber, cotton, beans, corn, and eggplant are damaged. Varieties vary in cold tolerance. To characterize the cold resistance of plants, the concept of the temperature minimum at which plant growth stops is used. For a large group of agricultural plants, its value is 4 °C. However, many plants have a higher temperature minimum and therefore are less resistant to cold.
Resistance to low temperatures is a genetically determined trait. The cold resistance of plants is determined by the ability of plants to maintain the normal structure of the cytoplasm, to change the metabolism during the period of cooling and the subsequent increase in temperature at a sufficiently high level.
Frost resistance - the ability of plants to tolerate temperatures below 0 ° C, low negative temperatures. Frost-resistant plants are able to prevent or reduce the effect of low negative temperatures. frosts in winter period with temperatures below -20 ° C are common for a significant part of the territory of Russia. Annual, biennial and perennial plants are exposed to frost. Plants endure winter conditions in different periods of ontogeny. In annual crops, seeds (spring plants), sprouted plants (winter crops) overwinter, in biennial and perennial crops - tubers, root crops, bulbs, rhizomes, adult plants. The ability of winter, perennial herbaceous and woody fruit crops to overwinter is due to their rather high frost resistance. The tissues of these plants may freeze, but the plants do not die.
The ability of plants to tolerate negative temperatures is determined by the hereditary basis of a given plant species, however, the frost resistance of one and the same plant depends on the conditions preceding the onset of frost, affecting the nature of ice formation. Ice can form both in the cell protoplast and in the intercellular space. Not all ice formation causes plant cells to die.
A gradual decrease in temperature at a rate of 0.5-1 °C/h leads to the formation of ice crystals, primarily in the intercellular spaces, and initially do not cause cell death. However, the consequences of this process can be detrimental to the cell. The formation of ice in the protoplast of the cell, as a rule, occurs with a rapid decrease in temperature. Coagulation of protoplasmic proteins occurs, cell structures are damaged by ice crystals formed in the cytosol, cells die. Plants killed by frost after thawing lose turgor, water flows out of their fleshy tissues.
Frost-resistant plants have adaptations that reduce cell dehydration. With a decrease in temperature, such plants show an increase in the content of sugars and other substances that protect tissues (cryoprotectors), these are primarily hydrophilic proteins, mono- and oligosaccharides; decrease in cell hydration; an increase in the amount of polar lipids and a decrease in the saturation of their fatty acid residues; an increase in the number of protective proteins.
The degree of frost resistance of plants is greatly influenced by sugars, growth regulators and other substances formed in the cells. In overwintering plants, sugars accumulate in the cytoplasm, and the starch content decreases. The influence of sugars on increasing the frost resistance of plants is multifaceted. Accumulation of sugars prevents freezing of a large volume of intracellular water, significantly reduces the amount of ice formed.
The property of frost resistance is formed in the process of plant ontogenesis under the influence of certain environmental conditions in accordance with the plant genotype, associated with a sharp decrease in growth rates, the transition of the plant to a dormant state.
The life cycle of development of winter, biennial and perennial plants is controlled by the seasonal rhythm of light and temperature periods. Unlike spring annual plants, they begin to prepare for the transfer of unfavorable conditions. winter conditions from the moment of cessation of growth and then during the autumn during the onset of low temperatures.
The direct effect of frost on cells is not the only danger that threatens perennial herbaceous and woody crops, winter plants during the winter. In addition to the direct effect of frost, plants are exposed to a number of other adverse factors. Temperatures can fluctuate significantly during winter. Frosts are often replaced by short-term and long-term thaws. IN winter time snow storms are not uncommon, and in snowless winters in the more southern regions of the country - and dry winds. All this depletes the plants, which, after overwintering, come out very weakened and may subsequently die.
Especially numerous adverse effects are experienced by herbaceous perennial and annual plants. On the territory of Russia, in unfavorable years, the death of winter grain crops reaches 30-60%. Not only winter crops are dying, but also perennial grasses, fruit and berry plantations. In addition to low temperatures, winter plants are damaged and die from a number of other adverse factors in winter and early spring: wetting, wetting, ice crust, bulging, damage from winter drought.
Damping out. Among the listed adversities, the first place is occupied by the decay of plants. The death of plants from damping off is observed mainly in warm winters with a large snow cover that lasts 2-3 months, especially if the snow falls on wet and thawed ground. Studies have shown that the cause of the death of winter crops from damping off is the depletion of plants. Being under snow at a temperature of about 0 ° C in a highly humid environment, almost complete darkness, i.e., under conditions in which the respiration process is quite intense and photosynthesis is excluded, plants gradually consume sugar and other nutrient reserves accumulated during the period passing through the first phase of hardening, and die from exhaustion (the content of sugars in tissues decreases from 20 to 2-4%) and spring frosts. Such plants are easily damaged by snow mold in spring, which also leads to their death.
Wetting. Wetting occurs mainly in spring in low places during the period of snow melting, less often during prolonged thaws, when melt water accumulates on the soil surface, which is not absorbed into the frozen soil and can flood plants. In this case, the cause of plant death is a sharp lack of oxygen (anaerobic conditions - hypoxia). In plants that are under a layer of water, normal respiration stops due to a lack of oxygen in water and soil. The absence of oxygen enhances the anaerobic respiration of plants, as a result of which toxic substances can be formed and the plants die from exhaustion and direct poisoning of the body.
Death under the ice crust. Ice crust forms on fields in areas where frequent thaws are replaced by severe frosts. The effect of soaking in this case may be aggravated. In this case, the formation of hanging or ground (contact) ice crusts occurs. Hanging crusts are less dangerous, since they form on top of the soil and practically do not come into contact with plants; they are easy to destroy with a roller.
When a continuous ice contact crust is formed, the plants completely freeze into the ice, which leads to their death, since the plants, already weakened from soaking, are subjected to very strong mechanical pressure.
Bulging. Damage and death of plants from bulging are determined by ruptures in the root system. Bulging of plants is observed if frosts occur in autumn in the absence of snow cover or if there is little water in the surface layer of the soil (during autumn drought), as well as during thaws if snow water has time to be absorbed into the soil. In these cases, the freezing of water does not begin from the surface of the soil, but at a certain depth (where there is moisture). The layer of ice formed at a depth gradually thickens due to the continued flow of water through the soil capillaries and raises (bulges out) the upper layers of the soil along with the plants, which leads to the breakage of the roots of plants that have penetrated to a considerable depth.
Winter drought damage. A stable snow cover protects winter cereals from drying out in winter. However, in conditions of snowless or little snowy winters, like fruit trees and shrubs, in a number of regions of Russia they are often in danger of excessive drying out by constant and strong winds, especially at the end of winter with significant heating by the sun. The fact is that the water balance of plants develops extremely unfavorably in winter, since the flow of water from frozen soil practically stops.
To reduce the evaporation of water and the adverse effects of winter drought, fruit tree species form a thick layer of cork on the branches and shed their leaves for the winter.
Photoperiodic responses to seasonal changes in day length are important for the flowering frequency of many species in both temperate and tropical regions. However, it should be noted that among the species of temperate latitudes that exhibit photoperiodic responses, there are relatively few spring-flowering ones, although we constantly encounter a significant number of "flowers blooming in spring", and many of these spring-flowering forms, for example, Ficariaverna, primrose (Primulavutgaris), violets (species of the genus Viola), etc., show pronounced seasonal behavior, remaining vegetative for the remainder of the year after abundant spring flowering. It can be assumed that spring flowering is a reaction to short days in winter, but for many species, this does not appear to be the case.
Of course, the length of the day is not the only external factor changing during the year. It is clear that temperature also exhibits marked seasonal variations, especially in the temperate regions, although there are considerable fluctuations in this factor, both daily and yearly. We know that seasonal changes in temperature, as well as changes in day length, have a significant impact on the flowering of many plant species.
It has been found that many species, including winter annuals, as well as biennial and perennial herbaceous plants, need to be chilled to transition to flowering.
Winter annuals and biennials are known to be monocarpic plants that require vernalization - they remain vegetative during the first growing season and bloom the following spring or early summer in response to the cooling period received in winter. The need for refrigeration of biennial plants to induce flowering has been experimentally demonstrated in a number of species such as beetroot (Betavulgaris), celery (Apiutngraveolens), cabbage and other cultivated varieties of the genus Brassica, bluebell (Campanulamedium), moonflower (Lunariabiennis), foxglove (Digitalispurpurea) and other. If foxglove plants, which under normal conditions behave like biennials, that is, bloom in the second year after germination, are kept in a greenhouse, they can remain vegetative for several years. In areas with mild winter Cabbage can grow outdoors for several years without the “arrowhead” (i.e. flowering) in spring, which usually occurs in areas with cold winters. Such species necessarily require vernalization, but in a number of other species flowering is accelerated when exposed to cold, but it can also occur without vernalization; such species showing facultative need for cold include lettuce (Lactucasaiiva), spinach (Spinacia oleracea) and late-flowering peas (Pistimsa-tivum).
As well as biennials, many perennials require cold exposure and will not flower without an annual winter chill. Of the common perennial plants, primrose (Primulavulgaris), violets (Violaspp.), lacfiol (Cheiranthuscheirii and C. allionii), levka (Mathiolaincarna), some varieties of chrysanthemums (Chrisanthemummorifolium), species of the genus Aster, Turkish carnation (Dianthus ), chaff (Loliumperenne). Perennial species require revernalization every winter.
It is likely that other spring-blooming perennials can be found to need refrigeration. Bulbous spring-blooming plants such as daffodils, hyacinths, blueberries (Endymionnonscriptus), crocuses, etc. do not require refrigeration to flower initiation because the flower primordial has been established in the bulb the previous summer, but their growth is highly dependent on temperature conditions . For example, in a tulip, the beginning of flowering is favored by relatively high temperatures (20°C), but for stem elongation and leaf growth, the optimal temperature at first is 8-9°C, with a gradual increase in later stages to 13, 17 and 23°C. Similar reactions to temperature are characteristic of hyacinths and daffodils.
In many species flower initiation does not occur during the cooling period itself, and begins only after the plant has been exposed to the higher temperatures following the cooling.
Thus, although the metabolism of most plants slows down considerably at low temperatures, there is no doubt that vernalization involves active physiological processes, the nature of which is as yet completely unknown.
Heat resistance (heat tolerance) - the ability of plants to endure the action of high temperatures, overheating. This is a genetically determined trait. Plant species differ in their tolerance to high temperatures.
According to heat resistance, three groups of plants are distinguished.
Heat-resistant - thermophilic blue-green algae and bacteria of hot mineral springs, capable of withstanding temperatures up to 75-100 °C. The heat resistance of thermophilic microorganisms is determined by a high level of metabolism, an increased content of RNA in cells, and resistance of the cytoplasmic protein to thermal coagulation.
Heat-tolerant - plants of deserts and dry habitats (succulents, some cacti, members of the Crassula family), withstanding heating by sunlight up to 50-65ºС. The heat resistance of succulents is largely determined by the increased viscosity of the cytoplasm and the content of bound water in the cells, and reduced metabolism.
Non-heat-resistant - mesophytic and aquatic plants. Mesophytes of open places tolerate short-term exposure to temperatures of 40-47 °C, shaded places - about 40-42 °C, aquatic plants withstand temperatures up to 38-42 °C. Of the agricultural crops, heat-loving plants of southern latitudes (sorghum, rice, cotton, castor beans, etc.) are the most heat-tolerant.
Many mesophytes tolerate high air temperatures and avoid overheating due to intensive transpiration, which reduces the temperature of the leaves. More heat-resistant mesophytes are distinguished by increased viscosity of the cytoplasm and increased synthesis of heat-resistant enzyme proteins.
Plants have developed a system of morphological and physiological adaptations that protect them from thermal damage: a light surface color that reflects insolation; folding and twisting of leaves; pubescence or scales that protect deeper tissues from overheating; thin layers of cork tissue that protect the phloem and cambium; greater thickness of the cuticular layer; high content of carbohydrates and low - water in the cytoplasm, etc.
Plants react very quickly to heat stress by inductive adaptation. They can prepare for exposure to high temperatures in a few hours. So, on hot days, the resistance of plants to high temperatures in the afternoon is higher than in the morning. Usually this resistance is temporary, it does not consolidate and disappears quite quickly if it gets cool. The reversibility of thermal exposure can range from several hours to 20 days. During the formation of generative organs, the heat resistance of annual and biennial plants decreases.
Droughts have become a common occurrence for many regions of Russia and the CIS countries. Drought is a long rainless period, accompanied by a decrease in relative air humidity, soil moisture and an increase in temperature, when the normal water needs of plants are not met. On the territory of Russia, there are regions of unstable moisture with an annual rainfall of 250-500 mm and arid regions, with a rainfall of less than 250 mm per year with an evaporation rate of more than 1000 mm.
Drought resistance - the ability of plants to endure long dry periods, significant water deficit, dehydration of cells, tissues and organs. At the same time, the damage to the crop depends on the duration of the drought and its intensity. Distinguish between soil drought and atmospheric drought.
Soil drought is caused by prolonged lack of rain combined with high air temperature and solar insolation, increased evaporation from the soil surface and transpiration, and strong winds. All this leads to desiccation of the root layer of the soil, a decrease in the supply of water available to plants at low air humidity. Atmospheric drought is characterized by high temperature and low relative humidity (10-20%). Severe atmospheric drought is caused by the movement of masses of dry and hot air - dry wind. Haze leads to serious consequences when a dry wind is accompanied by the appearance of soil particles in the air (dust storms).
Atmospheric drought, sharply increasing the evaporation of water from the soil surface and transpiration, contributes to the violation of the consistency of the rates of water entering from the soil into the aboveground organs and its loss by the plant, as a result, the plant wilts. However, when good development root system atmospheric drought does not cause plants great harm, if the temperature does not exceed the limit tolerated by plants. Prolonged atmospheric drought in the absence of rain leads to soil drought, which is more dangerous for plants.
Drought resistance is due to the genetically determined adaptability of plants to habitat conditions, as well as adaptation to a lack of water. Drought resistance is expressed in the ability of plants to endure significant dehydration due to the development of high water potential of tissues with the functional preservation of cellular structures, as well as due to the adaptive morphological features of the stem, leaves, generative organs, which increase their endurance, tolerance to the effects of prolonged drought.
Plants of arid regions are called xerophytes (from the Greek xeros - dry). They are able in the process of individual development to adapt to atmospheric and soil drought. The characteristic features of xerophytes are the small size of their evaporating surface, as well as the small size of the above-ground part compared to the underground. Xerophytes are usually herbs or stunted shrubs. They are divided into several types. We present the classification of xerophytes according to P. A. Genkel.
Succulents are very resistant to overheating and resistant to dehydration, during a drought they do not lack water, because they contain a large amount of it and slowly consume it. Their root system is branched in all directions in the upper layers of the soil, due to which the plants quickly absorb water during rainy periods. These are cacti, aloe, stonecrop, young.
Euxerophytes are heat-resistant plants that tolerate drought well. This group includes such steppe plants as Veronica gray, hairy aster, blue wormwood, watermelon colocynth, camel thorn, etc. They have low transpiration, high osmotic pressure, the cytoplasm is highly elastic and viscous, the root system is very branched, and its the mass is placed in the upper soil layer (50-60 cm). These xerophytes are capable of shedding leaves and even entire branches.
Hemixerophytes, or semi-xerophytes, are plants that are unable to tolerate dehydration and overheating. The viscosity and elasticity of their protoplast is insignificant, it is characterized by high transpiration, a deep root system that can reach subsoil water, which ensures an uninterrupted supply of water to the plant. This group includes sage, common cutter, etc.
Stipakserofshpy are feather grass, tyrsa and other narrow-leaved steppe grasses. They are resistant to overheating, make good use of the moisture of short-term rains. Withstand only short-term lack of water in the soil.
Poikiloxerophytes are plants that do not regulate their water regime. These are mainly lichens, which can dry out to an air-dry state and become active again after rains.
Hygrophytes (from the Greek hihros - wet). Plants belonging to this group do not have adaptations that limit water consumption. Hygrophytes are characterized by relatively large cell sizes, thin-walled shell, weakly lignified walls of vessels, wood and bast fibers, thin cuticle and slightly thickened outer walls of the epidermis, large stomata and a small number of them per unit surface, large leaf blade, poorly developed mechanical tissues, a rare network of veins in the leaf, large cuticular transpiration, long stem, underdeveloped root system. By structure, hygrophytes approach shade-tolerant plants, but have a peculiar hygromorphic structure. A slight lack of water in the soil causes rapid wilting of hygrophytes. The osmotic pressure of cell sap in them is low. These include mannik, wild rosemary, cranberries, sucker.
According to the conditions of growth and structural features, plants with leaves partially or completely immersed in water or floating on its surface, which are called hydrophytes, are very close to hygrophytes.
Mesophytes (from the Greek mesos - medium, intermediate). Plants of this ecological group grow in conditions of sufficient moisture. The osmotic pressure of cell sap in mesophytes is 1-1.5 thousand kPa. They wilt easily. Mesophytes include most meadow grasses and legumes - creeping couch grass, meadow foxtail, meadow timothy, blue alfalfa, etc. From field crops, hard and soft wheat, corn, oats, peas, soybeans, sugar beet, hemp, almost all fruit (with the exception of almonds, grapes), many vegetable crops(carrots, tomatoes, etc.).
Transpiring organs - leaves are characterized by significant plasticity; depending on the growing conditions in their structure, quite large differences are observed. Even the leaves of the same plant with different water supply and lighting have differences in structure. Certain patterns have been established in the structure of leaves, depending on their location on the plant.
V. R. Zalensky discovered changes in the anatomical structure of leaves by tiers. He found that the leaves of the upper tier show regular changes in the direction of increased xeromorphism, i.e., structures are formed that increase the drought resistance of these leaves. The leaves located in the upper part of the stem always differ from the lower ones, namely: the higher the leaf is located on the stem, the smaller the size of its cells, the greater the number of stomata and the smaller their size, the greater the number of hairs per unit surface, the denser the network of vascular bundles, the stronger palisade tissue is developed. All these signs characterize xerophilia, i.e., the formation of structures that contribute to an increase in drought resistance.
Physiological features are also associated with a certain anatomical structure, namely: the upper leaves are distinguished by a higher assimilation ability and more intensive transpiration. The concentration of juice in the upper leaves is also higher, and therefore water can be drawn away from the lower leaves by the upper leaves, drying and dying of the lower leaves. The structure of organs and tissues that increases the drought resistance of plants is called xeromorphism. Distinctive features in the structure of the leaves of the upper tier are explained by the fact that they develop in conditions of somewhat difficult water supply.
A complex system of anatomical and physiological adaptations has been formed to equalize the balance between the inflow and outflow of water in the plant. Such adaptations are observed in xerophytes, hygrophytes, mesophytes.
The results of the research showed that the adaptive properties of drought-resistant plant forms arise under the influence of the conditions of their existence.
The amazing harmony of living nature, its perfection are created by nature itself: the struggle for survival. Forms of adaptations in plants and animals are infinitely diverse. From the time of its appearance, the entire animal and plant world has been improving along the path of expedient adaptations to living conditions: to water, air, sunlight, gravity, etc.
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3. Prokofiev A.A. "Problems of drought resistance of plants", Moscow, Nauka, 1978.
4. Sergeeva K.A. "" Physiological and biochemical bases of winter hardiness of woody plants "", Moscow, Nauka, 1971
5. Kultiasov I.M. Ecology of plants. - M.: Publishing House of Moscow University, 1982
