The influence of thermal conditions on plant growth and fertilizer efficiency. Presentation on the topic: “The effect of extreme temperatures on plants

Good day, dear friends!

We will talk about the effect of heat on plants in this article.

Often reasons poor growth and plant development is caused by excess or lack of heat. Low or too high temperatures sometimes cause irreversible processes in plant tissues. They are associated with changes in the structure of protein molecules in plant cells.

The changes that occur can be corrected in time if you correctly adjust the temperature intensity and use additional measures. For example, in conditions of excess heat, it is recommended not only to shade the suffering plants, creating coolness, but also to spray more often. To prevent hypothermia, you should consider temporary greenhouses or shelters for plants.

The effect of lack of heat on plants

In different cultures, extreme values of the same factor can cause various changes. For example, low temperature causes reddening of leaves, causes chlorosis in ageratum and primroses, and cracks in stems and leaves in lilies. For irises, an early drop in temperature in autumn is also dangerous. In such conditions, flowers may develop rot of the root collar of the rhizomes. In general, when there is a lack of heat, almost all plants experience stunted growth.

Some heat-loving crops, which are grown outdoors in the summer, cannot withstand even a short-term lack of heat. Cold temperatures down to -1°C cause their above-ground organs to freeze. These species include many southern plants that are grown in containers (yucca, palms, agaves) and carpet plants (clenia, echeveria, alternanthera).

The effect of excess heat on plants

Too high temperatures are no less dangerous. This is especially true for bulbous and corm plants that have just been planted in the ground. Excess heat inhibits the development and growth of the root system. As a result, the underdeveloped underground part is unable to absorb required amount chemical compounds from the soil. The aerial part of the bulbous plants begins to rapidly suffer from lack of nutrition. The buds that appear cannot for a long time bloom and eventually dry out. The roots of such plants rot and die.

It has been noticed that not only bulbous plants, but also most flower crops at the beginning of the growing season require lower temperature values than in other periods. At the same time, at night all plants are more resistant to lack of heat than in the daytime.

Among all ornamental and horticultural crops, plants stand out that can safely tolerate both low and high temperatures. These include dracaena, aloe, clivia, aspidistra, epiphyllum, phyllocactus. Such plants can be safely grown in both relatively cold and hot rooms.

So, we can conclude that basically effect of heat on plants is very large, so it is necessary to try to create the most acceptable temperature regime. See you later, friends!

For most plants, the most favorable temperatures for life are +15...+30 o C. At temperatures +35...+40 o C, most plants are damaged.

The effect of high temperatures entails whole line dangers for plants: severe dehydration and desiccation, burns, destruction of chlorophyll, irreversible respiratory disorders and other physiological processes, cessation of protein synthesis and increased breakdown, accumulation of toxic substances, in particular ammonia. At very high temperatures, the permeability of membranes sharply increases, and then thermal denaturation of proteins, coagulation of the cytoplasm and cell death occurs. Overheating of the soil leads to damage and death of superficially located roots, and to burns of the root collar.

Primary changes in cellular structures occur at the membrane level as a result of activation of the formation of oxygen radicals and subsequent lipid peroxidation, disruption of the antioxidant system - the activity of superoxide dismutase, glutathione reductase and other enzymes. This causes the destruction of protein-lipid complexes of the plasmalemma and other cell membranes, leads to loss of osmotic properties of the cell. As a result, disorganization of many cell functions and a decrease in the speed of various physiological processes are observed. Thus, at a temperature of 20 o C, all cells undergo the process of mitotic division, at 38 o C, mitosis is observed in every seventh cell, and an increase in temperature to 42 o C reduces the number of dividing cells by 500 times.

At maximum temperatures, the consumption of organic substances for respiration exceeds its synthesis, the plant becomes poor in carbohydrates, and then begins to starve. This is especially pronounced in plants of more temperate climates (wheat, potatoes, many garden crops). With general weakening, their susceptibility to fungal and viral infections increases.

Even a short-term stressful effect of high temperature causes a restructuring of the hormonal system of plants. Using the example of wheat and pea seedlings, it was established that heat shock induces a cascade of multi-stage changes in the hormonal system, which is triggered by the release of IAA from the pool of its conjugates, which acts as a stress signal and initiates ethylene synthesis. The result of ethylene synthesis is a subsequent decrease in the level of IAA and an increase in ABA. These hormonal changes apparently induce the synthesis of antioxidant enzymes and heat shock proteins, cause a decrease in growth rates and, as a result, the plant’s resistance to high temperatures increases.

There is a certain connection between plant habitat conditions and heat resistance. The drier the habitat, the higher the temperature maximum, the greater the heat resistance of plants.

Plants can prepare for exposure to high temperatures in a few hours. Thus, on hot days, plant resistance to high temperatures in the afternoon it is higher than in the morning. Usually this resistance is temporary, it is not fixed and disappears quite quickly if it gets cool. The reversibility of thermal effects can range from several hours to 20 days.

Heat resistance is also related to the stage of plant development: young, actively growing tissues are less resistant than old ones. High temperatures during the flowering period are especially dangerous. Almost all generative cells under these conditions undergo structural changes, lose activity and the ability to divide, deformation of pollen grains, poor development of the embryo sac and the appearance of sterile flowers are observed.

Plant organs also differ in heat resistance. Dehydrated organs tolerate elevated temperatures better: seeds up to 120 o C, pollen up to 70 o C, spores can withstand heating up to 180 o C for several minutes.

Of the tissues, cambial ones are the most resistant. Thus, the cambial layer in trunks tolerates temperatures up to +51 o C in summer.

Temperature is the most important factor determining the possibilities and timing of crop cultivation.

Biological and biological processes occurring in the soil chemical processes Transformations of batteries are directly dependent on temperature conditions. Heat supply to crops is characterized by the sum of average daily air temperatures above 10°C during the growing season. Both high and low temperatures disrupt the course of biochemical processes in cells, and thus can cause irreversible changes in them, leading to the cessation of growth and death of plants. An increase in temperature to 25-28°C increases the activity of photosynthesis, and with its further growth, respiration begins to noticeably predominate over photosynthesis, which leads to a decrease in plant weight. Therefore, most agricultural crops at temperatures above 30°C, wasting carbohydrates on respiration, as a rule, do not produce an increase in yield. Reducing the ambient temperature from 25 to 10°C reduces the intensity of photosynthesis and plant growth by 4-5 times. The temperature at which the formation of photosynthetic products is equal to their consumption for respiration is called the compensation point.

The highest intensity of photosynthesis in plants of temperate climates is observed in the range of 24-26°C. For most field crops, the optimal temperature during the day is 25°C, at night - 16-18°C. When the temperature rises to 35-40°C, photosynthesis stops as a result of disruption of biochemical processes and excessive transpiration (Kuznetsov, Dmitrieva, 2006). A significant deviation of temperature from the optimal one towards increasing or decreasing significantly reduces enzymatic activity in plant cells, the intensity of photosynthesis and the supply of nutrients to plants.

Temperature has a big impact on root growth. Low (< 5°С) и высокие (>30°C) soil temperatures contribute to the superficial location of roots, significantly reducing their growth and activity. In most plants, the most powerful branched root system is formed at a soil temperature of 20-25°C.

When determining the timing of fertilizer application, it is important to take into account the significant influence of soil temperature on the supply of nutrients to plants. It has been established that at temperatures below 12°C, the use of phosphorus, potassium and microelements from soil and fertilizers by plants is significantly impaired, and at temperatures below 8°C, the consumption of mineral nitrogen is also noticeably reduced. For most agricultural crops, a temperature of 5-6°C is critical for the supply of basic nutrients to the plants.

The heat supply of the growing season is largely determined by the structure of sown areas and the possibility of growing more productive late-ripening crops that can be used for a long time solar energy to form a crop or carry out repeated sowings after early harvested crops.

In the conditions of the Non-Chernozem Zone of Russia, there is a direct dependence of the productivity of agricultural crops on the sum of temperatures. In the forest-steppe and steppe zones, under irrigated conditions, no reliable connection has been established between the number of positive temperatures and agricultural yields. In the central and southern regions of the country, an increase or decrease in temperature by 2-3 °C does not have a significant effect on plant productivity.

Temperature also has a great influence on the vital activity of soil microflora, which determines the mineral nutrition of plants. It has been established that the greatest intensity of ammonification of organic residues in the soil under the influence of microorganisms occurs at a temperature of 26-30°C and soil moisture of 70-80% of HB. Deviation of temperature or humidity from optimal values significantly reduces the intensity of microbiological processes in the soil.

The moisture supply of plants has a great influence on the intensity of photosynthesis and the effectiveness of fertilizers. The degree of opening of stomata, the rate of entry of CO 2 into the leaves and the release of O 2 depend on the turgor state of plants. In conditions of drought and excessive humidity, the stomata usually close and the assimilation of carbon dioxide (photosynthesis) stops. The highest intensity of photosynthesis is observed with a slight water deficit in the leaf (10-15% of full saturation), when the stomata are maximally open. Only under conditions of optimal water regime does the root system of plants exhibit the highest activity in consuming nutrients from the soil solution. A lack of moisture in the soil leads to a decrease in the rate of movement of water and nutrients through the xylem to the leaves, the intensity of photosynthesis and a decrease in plant biomass.

Not only the amount of precipitation is important, but also the dynamics of its distribution during the growing season in relation to individual crops. The productivity of agricultural crops is largely determined by the availability of moisture during the most critical phases of plant growth and development.

For the Non-Chernozem Zone, a dark correlation has been established between yield and precipitation in late May - early June for grain crops, in July - August for potatoes, corn, root crops and vegetable crops. Lack of moisture during these periods significantly reduces plant yield and the effectiveness of fertilizers.

The use of nitrogen and phosphorus-potassium fertilizers significantly increases the moisture deficit, since in proportion to the increase in the yield of the above-ground mass, water consumption also increases. It has been established that in fertilized fields the drying effect of plants on the soil begins to manifest itself earlier and to a greater depth than in unfertilized fields. Therefore, when there is a moisture deficit, fertilized fields are sown as early as possible, so that by the time drought sets in and the top layer of soil dries out, the roots reach the lower, more moist horizons. The most important measures for moisture accumulation in steppe regions are snow retention, early harrowing to seal up moisture, and early sowing.

In the forest-steppe and dry-steppe zones, moisture availability is one of the the most important factors productivity of agricultural crops.

In zones of sufficient and excessive moisture, the leaching water regime has a great influence on the supply of nutrients to plants, since a significant amount of nitrogen, calcium, magnesium and soluble humic substances are removed from the root layer of soil with the downward flow of water. This regime is created, as a rule, in the fall and in early spring.

Great influence on crop yields, fertilizer efficiency, lines and agricultural techniques field work is influenced by the exposure and topography of the fields, since slopes of different exposure and steepness differ significantly in the content of humus and nutrients in the soil, thermal and water regimes and the responsiveness of agricultural plants to fertilizers. The soils of the northern and northeastern slopes, as a rule, are more humified, better provided with moisture, higher snow cover, thaw later compared to the southern slopes and, as a rule, have a heavier granulometric composition. The soils of the southern and southwestern slopes are warmer than the northern ones, thaw earlier, are characterized by intense flood runoff of melt and storm water, hence, as a rule, they are more eroded and contain fewer silt particles. In the soils of the southern slopes, the mineralization of stubble-root residues and organic fertilizers flows more intensely, so they are less humified. The higher the snow cover, the shallower the soil freezing depth, the better it absorbs spring melt water and floods destroy the soil less.

It is important to take into account the characteristics of soils of different exposures when planning the timing of field work and the need for equipment for applying fertilizers, since after completion of field work on the southern slopes it is used in fields with a northern exposure.

Despite the great dependence of the growth and development of plants on their supply of moisture and heat, the decisive role in the formation of agricultural yields in the Non-Black Earth Zone and many other regions belongs to soil fertility and the use of fertilizers.

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Ministry of Education of the Russian Federation

State educational institution

higher professional education

IRKUTSK STATE UNIVERSITY

(GOU VPO ISU)

Department of Hydrology

Effect of temperature on plants

Supervisor

Associate Professor, Ph.D. Mashanova O.Ya.

Voloshina V.V.

study group 6141

Irkutsk, 2010

Introduction

The adaptation of plant ontogeny to environmental conditions is the result of their evolutionary development (variability, heredity, selection). Throughout the phylogenesis of each plant species, in the process of evolution, certain individual needs for living conditions and adaptability to the ecological niche it occupies have developed. Moisture and shade tolerance, heat resistance, cold resistance and other ecological characteristics of specific plant species were formed during evolution as a result of long-term action of appropriate conditions. Thus, heat-loving plants and short-day plants are characteristic of southern latitudes, while plants that are less demanding of heat and long-day plants are characteristic of northern latitudes.

In nature, in one geographical region, each plant species occupies an ecological niche corresponding to its biological features: 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. Great importance have also external conditions of plant ontogenesis.

In most cases, plants and crops (plantings) of agricultural crops, experiencing the effects of certain unfavorable factors, show resistance to them as a result of adaptation to the conditions of existence that have developed historically.

1. Temperature as a biological factor

Plants are poikilothermic organisms, i.e. their own temperature is equalized with the temperature of their environment. However, this correspondence is incomplete. Of course, the heat released during respiration and used in synthesis is unlikely to play any ecological role, but still the temperature of the above-ground parts of the plant can differ significantly from the air temperature as a result of energy exchange with the environment. Thanks to this, for example, plants of the Arctic and high mountains, which inhabit places protected from the wind or grow close to the soil, have a more favorable thermal regime and can quite actively support metabolism and growth, despite constantly low air temperatures. Not only individual plants and their parts, but also entire phytocenoses sometimes exhibit characteristic deviations from air temperature. On one hot summer day in Central Europe, the temperature on the surface of the crowns in forests was 4 °C, and in meadows - 6 °C higher than the air temperature and 8 °C (forest) or 6 °C (meadow) lower than the surface temperature soil devoid of vegetation.

To characterize the thermal conditions of plant habitats, it is necessary to know the patterns of heat distribution in space and its dynamics over time, both in relation to general climatic characteristics and specific plant growth conditions.

A general idea of the provision of heat in a particular area is given by such general climatic indicators as the average annual temperature for a given area, the absolute maximum and absolute minimum (i.e., the highest and lowest temperatures recorded in this area), the average temperature of the warmest month ( in most of the northern hemisphere it is July, in the southern hemisphere it is January, on the islands and coastal areas it is August and February); the average temperature of the coldest month (in the continental regions of the northern hemisphere - January, in the southern hemisphere - July, in coastal regions - February and August).

To characterize the thermal living conditions of plants, it is important to know not only the total amount of heat, but also its distribution over time, on which the possibilities of the growing season depend. The annual dynamics of heat is well reflected by the course of average monthly (or average daily) temperatures, which are not the same at different latitudes and at different types climate, as well as the dynamics of maximum and minimum temperatures. The boundaries of the growing season are determined by the duration of the frost-free period, the frequency and degree of probability of spring and autumn frosts. Naturally, the vegetation threshold cannot be the same for plants with different attitudes to heat; for cold-resistant cultivated species, 5°C is conventionally accepted, for most crops in the temperate zone 10°C, for heat-loving species 15°C. It is believed that for natural vegetation of temperate latitudes the threshold temperature for the onset of spring phenomena is 5°C.

In general terms, the speed of seasonal development is proportional to the accumulated sum of temperatures (it is worth comparing, for example, the slow development of plants in a cold and long spring or the “explosive” beginning of spring during a strong heat wave). There are a number of deviations from this general pattern: for example, too high sums of temperatures no longer accelerate, but retard development.

2. Plant temperature

Along with the thermal characteristics of the environment, it is necessary to know the temperature of the plants themselves and its changes, since it is this that represents the true temperature background for physiological processes. Plant temperature is measured using electric thermometers with miniature semiconductor sensors. In order for the sensor not to affect the temperature of the organ being measured, its mass must be many times less than the mass of the organ. The sensor must also be low-inertia and quickly respond to temperature changes. Sometimes thermocouples are used for this purpose. Sensors are either applied to the surface of a plant, or “implanted” into stems, leaves, or under the bark (for example, to measure the temperature of the cambium). At the same time, be sure to measure the ambient air temperature (by shading the sensor).

Plant temperatures are highly variable. Due to turbulent flows and continuous changes in the temperature of the air directly surrounding the leaf, the action of wind, etc., the temperature of the plant varies over a range of several tenths or even whole degrees and with a frequency of several seconds. Therefore, “plant temperature” should be understood as a more or less generalized and fairly conventional value characterizing the general level of heating. Plants, as poikilothermic organisms, do not have their own stable body temperature. Their temperature is determined by the thermal balance, i.e., the ratio of energy absorption and release. These values depend on many properties of both the environment (size of radiation arrival, ambient air temperature and its movement) and the plants themselves (color and other optical properties of the plant, size and location of leaves, etc.). The primary role is played by the cooling effect of transpiration, which prevents very strong overheating in hot habitats. This can be easily demonstrated in experiments with desert plants: you just need to smear Vaseline on the surface of the leaf on which the stomata are located, and the leaf dies before your eyes from overheating and burns.

As a result of all these reasons, the temperature of plants usually differs (sometimes quite significantly) from the ambient temperature. In this case, three situations are possible:

· the plant temperature is higher than the ambient air temperature (“supratemperature” plants, according to O. Lange’s terminology),

below it (“sub-temperature”),

· equal or very close to it.

The first situation occurs quite often in a wide variety of conditions. A significant excess of plant temperature over air temperature is usually observed in massive plant organs, especially in hot habitats and with low transpiration. Large fleshy stems of cacti, thickened leaves of euphorbia, sedum, and juveniles, in which the evaporation of water is very insignificant, become very hot. Thus, at an air temperature of 40-45°C, desert cacti heat up to 55-60°C; in temperate latitudes on summer days, the succulent leaves of plants from the genera Sempervivum and Sedum often have a temperature of 45°C, and inside the rosettes of the young - up to 50°C. Thus, the temperature rise of the plant above the air temperature can reach 20°C.

Various fleshy fruits are strongly heated by the sun: for example, ripe tomatoes and watermelons are 10-15°C warmer than the air; the temperature of red fruits in mature cobs of arum - Arum maculatum reaches 50°C. There is quite a noticeable increase in temperature inside a flower with a more or less closed perianth, which retains the heat that is released during respiration from dissipation. Sometimes this phenomenon can have significant adaptive significance, for example, for flowers of forest ephemeroids (scilla, corydalis, etc.) in early spring, when the air temperature barely exceeds 0°C.

The temperature regime of such massive formations as tree trunks is also peculiar. In solitary trees, as well as in deciduous forests, during the “leafless” phase (spring and autumn), the surface of the trunks heats up greatly during the daytime, and to the greatest extent on the south side; The cambium temperature here can be 10-20°C higher than on the northern side, where it is at ambient temperature. On hot days, the temperature of dark spruce trunks rises to 50-55°C, which can lead to cambium burns. The readings of thin thermocouples implanted under the bark made it possible to establish that the trunks of tree species are protected in different ways: in birch, the cambium temperature changes more quickly in accordance with fluctuations in the outside air temperature, while in pine it is more constant due to the better heat-shielding properties of the bark. The heating of tree trunks and leafless spring forests significantly affects the microclimate of the forest community, since trunks are good heat accumulators.

The excess of plant temperature over air temperature occurs not only in highly heated, but also in colder habitats. This is facilitated by the dark color or other optical properties of plants, which increase the absorption of solar radiation, as well as anatomical and morphological features that help reduce transpiration. Arctic plants can warm up quite noticeably: one example is the dwarf willow - Salix arctica in Alaska, whose leaves are 2-11°C warmer than the air during the day and even at night during the polar “24-hour day” - by 1-3°C. Another interesting example heating under snow: in summer time in Antarctica, the temperature of lichens can be above 0°C even under a layer of snow of more than 30 cm. Obviously, in such harsh conditions natural selection retained forms with the darkest color, in which, thanks to such heating, a positive balance of carbon dioxide gas exchange is possible.

The needles of coniferous trees can be heated quite significantly by the sun's rays in winter: even with negative temperatures it is possible to exceed the air temperature by 9-12°C, which creates favorable opportunities for winter photosynthesis. It was experimentally shown that if a strong flow of radiation is created for plants, then even at a low temperature of the order of - 5, - 6 ° C, the leaves can heat up to 17-19 ° C, i.e., photosynthesize at quite “summer” temperatures.

A decrease in plant temperature compared to the surrounding air is most often observed in highly illuminated and heated habitats (steppes, deserts), where the leaf surface of plants is greatly reduced, and increased transpiration helps remove excess heat and prevents overheating. In intensively transpiring species, leaf cooling (the difference with air temperature) reaches 15°C. This is an extreme example, but a decrease of 3-4°C can protect against harmful overheating.

In the most general terms, we can say that in hot habitats the temperature of the above-ground parts of plants is lower, and in cold habitats it is higher than the air temperature. This pattern can be traced in the same species: for example, in the cold mountain belt North America, at altitudes of 3000-3500 m, the plants are warmer, and in the low mountains the air is colder.

The coincidence of plant temperature with the ambient air temperature is much less common under conditions that exclude a strong influx of radiation and intense transpiration, for example in herbaceous plants under the canopy of shady forests (but not in the glare of the sun), and in open habitats - in cloudy weather or in the rain.

There are different biological types of plants in relation to temperature. In thermophilic, or megathermic (heat-loving) plants, the optimum lies in the region of elevated temperatures. They live in tropical and subtropical climates, and in temperate zones- in highly heated habitats. Low temperatures are optimal for cryophilic or microthermal (cold-loving) plants. These include species that live in polar and high-mountain regions or occupy cold ecological niches. Sometimes an intermediate group of mesothermic plants is distinguished.

3. Effect of temperature stress

Heat and frost harm vital functions and limit the spread of the species depending on their intensity, duration and frequency, but above all on the state of activity and the degree of hardening of the plants. Stress is always an unusual load, which does not necessarily have to be life-threatening, but which certainly causes an “alarm reaction” in the body, unless it is in a pronounced state of numbness. Dormant stages, such as dry spores, as well as poikilohydric plants in a dried state, are insensitive, so that they can survive without damage any temperature recorded on Earth.

Protoplasm initially responds to stress with a sharp increase in metabolism. An increase in breathing intensity, which is observed as a stress reaction, reflects an attempt to correct existing defects and create ultrastructural prerequisites for adaptation to a new situation. A stress reaction is a struggle between adaptation mechanisms and destructive processes in protoplasm leading to its death.

Cell death from overheating and cold

If the temperature passes a critical point, cellular structures and functions can be damaged so suddenly that the protoplasm immediately dies. In nature, such sudden destruction often occurs during episodic frosts, such as late frosts in the spring. But damage can also occur gradually; individual vital functions are thrown out of balance and inhibited until, finally, the cell dies as a result of the cessation of vital processes.

3.1 Damage pattern

Different life processes are not equally sensitive to temperature. First, the movement of protoplasm stops, the intensity of which directly depends on the energy supply due to respiration processes and on the presence of high-energy phosphates. Then photosynthesis and respiration decrease. Heat is especially dangerous for photosynthesis, while respiration is most sensitive to cold. In plants damaged by cold or heat, respiration levels fluctuate greatly after returning to temperate conditions and are often abnormally elevated. Damage to chloroplasts leads to long-term or irreversible inhibition of photosynthesis. In the final stage, the semi-permeability of biomembranes is lost, cellular compartments are destroyed, especially plastid thylakoids, and cell sap is released into the intercellular spaces.

3.2 Causes of death due to overheating

High temperature quickly leads to death due to membrane damage and primarily as a result of inactivation and denaturation of proteins. Even if only a few, especially thermolabile enzymes fail, this leads to a disorder in the metabolism of nucleic acids and proteins and, ultimately, also to cell death. Soluble nitrogen compounds accumulate in such high concentrations that they diffuse out of the cells and are lost; In addition, toxic decomposition products are formed, which can no longer be neutralized during metabolism.

3.3 Death from cooling and frost

plant temperature overheating frost

When protoplasm is damaged by cold, one must distinguish whether it is caused by the low temperature itself or by freezing. Some plants of tropical origin are damaged even when the temperature drops to a few degrees above zero. Like death from overheating, death from cooling is also primarily associated with disorganization of the metabolism of nucleic acids and proteins, but disturbances in permeability and cessation of the flow of assimilates also play a role here.

Plants that are not harmed by cooling to temperatures above zero are damaged only at temperatures below zero, that is, as a result of the formation of ice in the tissues. Water-rich, unhardened protoplasts can freeze easily; In this case, ice crystals instantly form inside the cell, and the cell dies. Most often, ice is formed not in protoplasts, but in intercellular spaces and cell walls. This ice formation is called extracellular. Crystallized ice acts like dry air, since the vapor pressure above the ice is lower than above the supercooled solution. As a result, water is taken away from the protoplasts, they are greatly compressed (by 2/3 of their volume) and the concentration of dissolved substances in them increases. The movement of water and freezing continue until an equilibrium of suction forces between ice and water is established in the protoplasm. The equilibrium position depends on temperature; at a temperature of -5°C, equilibrium occurs at approximately; 60 bar, and at - 10 ° C - already at 120 bar. Thus, low temperatures act on protoplasm in the same way as desiccation. The frost resistance of the cell is higher if the water is firmly bound to the structures of the protoplasm and is osmotically bound. When the cytoplasm is dehydrated (it makes no difference whether as a result of drought or freezing), membrane-associated enzyme systems are inactivated - systems primarily involved in ATP synthesis and phosphorylation processes (Heber and Santarius, 1979). Inactivation is caused by excessive and therefore toxic concentrations of ions. salts and organic acids in the unfrozen residual solution. On the contrary, sugars, sugar derivatives, certain amino acids and proteins protect biomembranes and enzymes from harmful substances (Maksimov, Tumanov, Krasavtsev, 1952). Along with this, there are indications that proteins become denatured when frozen, which also leads to membrane damage (Levitt 1980).

3.4 Thermal stability

Thermal tolerance is the body's ability to tolerate extreme heat or cold without permanent damage. Thermal resistance of a plant consists of the ability of protoplasm to tolerate extreme temperatures (tolerance according to J. Levitt) and the effectiveness of measures that slow down or prevent the development of damage (avoidance).

Measures to avoid damage

Possible ways to protect cells from temperature damage are few and not very effective. Insulation against overheating and cooling can only provide short-term protection. Thus, for example, in the dense crowns of trees or in cushion plants, the buds of leaves and flowers located deep and closer to the ground are less in danger of freezing as a result of the loss of heat by radiation than the outer parts of the plant. Conifer species with particularly thick bark are better able to withstand fires in the undergrowth. Two protective measures are of general importance: slowing down the formation of ice in tissues and (in hot weather) cooling by reflecting incident rays and using transpiration.

3.5 Stability of protoplasm

Plants can withstand prolonged and regularly repeated exposure to extreme temperatures only if the protoplasm itself is heat- or frost-resistant. This feature is genetically determined and therefore different types and even varieties are expressed to varying degrees. However, this is not a property that is inherent in the plant constantly and always to the same extent. Seedlings, spring shoots of woody plants during the period of their intense elongation, microbial cultures in the exponential growth phase are unlikely to be able to harden and are therefore extremely sensitive to temperature.

Ice resistance and frost hardening

In areas with seasonal climate land plants acquire “ice resistance” in the fall, i.e., the ability to tolerate the formation of ice in the tissues. In the spring, with the buds opening, they again lose this ability, and now freezing leads to their freezing. Thus, the cold resistance of perennial plants outside the tropics regularly fluctuates throughout the year between a minimum value during the growing season and a maximum during the growing season. winter time. Ice resistance develops gradually in autumn. The first prerequisite for this is the transition of the plant to a state of readiness for hardening, which occurs only when growth ends. If readiness for hardening has been achieved, then the hardening process can begin. This process consists of several phases, each of which prepares the transition to the next. Hardening to frost, in winter cereals and fruits; trees (these plants have been studied most thoroughly) begins with multi-day (up to several weeks) exposure to temperatures just above zero. At this phase, preceding hardening, sugars and other protective substances accumulate in the protoplasm, the cells become poorer in water, and the central vacuole breaks up into many small vacuoles. Thanks to this, the protoplasm is prepared for the next phase, which takes place during regular mild frosts from - 3 to - 5 ° C. In this case, the ultrastructures and enzymes of the protoplasm are rearranged in such a way that the cells tolerate dehydration associated with the formation of ice. Only after this can plants, without being exposed to danger, enter the final phase of the process; hardening, which, with continuous frost of at least -10 to -15 ° C, makes protoplasm extremely frost-resistant.

Effective temperature zones are different for different species. Birch seedlings ready for hardening, which before the start of the hardening process would have frozen out at a temperature of - 15 to - 20 ° C, are transferred after the end of the first hardening phase; already - 35 °C, and when fully hardened, they can even withstand cooling to - 195 °C. Thus, the cold itself stimulates the hardening process. If the frost weakens, then the protoplasm again enters the first phase of hardening, however, resistance can again be raised by cold periods to highest level while the plants remain dormant.

IN winter period The seasonal course of frost resistance is superimposed on short-term (induced) adaptations, thanks to which the level of resistance quickly adapts to weather changes. Cold contributes most to hardening at the beginning of winter. At this time, resistance can rise to its highest level in a few days. A thaw, especially at the end of winter, causes a rapid decrease in the resistance of plants, but in the middle of winter, after being kept for several days at a temperature of +10 to +20 ° C, the plants lose their hardening to a significant extent. The ability to change frost resistance under the influence of cold and heat, i.e., the range of induced resistance adaptations, is a constitutional trait individual species plants.

After the end of winter dormancy, the ability to harden and at the same time a high degree of hardening are quickly lost. In spring there is a close connection between the activation of bud break and the progress of resistance changes

Conclusion

The forms of adaptations in plants are infinitely diverse. All vegetable world Since its appearance, it has been improving along the path of expedient adaptations to living conditions.

Plants are poikilothermic organisms. Damage begins at the molecular level with dysfunction of proteins and nucleic acids. Temperature is a factor that seriously affects the morphology and physiology of plants, requiring changes in the plant itself that could adapt it. Adaptations of plants to different temperature conditions, even within the same species, are different.

At high temperatures, adaptations such as dense leaf pubescence, a shiny surface, a decrease in the surface that absorbs radiation, a change in position relative to the heat source, increased transpiration, a high content of protective substances, a shift in the temperature optimum of the activity of the most important enzymes, a transition to a state of suspended animation, occupation microniches protected from insolation and overheating, shifting the growing season to a season with more favorable thermal conditions.

Adaptations to cold are as follows: pubescence of bud scales, thick cuticle, thickening of the cork layer, pubescence of leaves, closing of rosette leaves at night, development of dwarfism, development of creeping forms, cushion growth form, development of contractile roots, increased concentration of cell sap, increased proportion of colloid-bound water , suspended animation

According to different heat resistance, species are distinguished: non-cold-resistant, non-frost-resistant, ice-resistant, non-heat-resistant, heat-tolerant zukaryotes, heat-tolerant prokaryotes.

List of used literature

1. Alexandrov V.Ya. Cells, macromolecules and temperature. L.: Nauka, 1975. 328 s

2. Voznesensky V.L., Reinus R.M. Temperature of assimilating organs of desert plants // Bot. zhurn., 1977; t. 62. N 6

3. Goryshina T.K. Early spring ephemeroids of forest-steppe oak forests. L., Publishing house Leningr. un-ta. 1969

4. Goryshina T.N. Ecology of plants uch. A manual for universities, Moscow, V.

5. Kultiasov I.M. Plant ecology M.: Moscow University Publishing House, 1982 33-89 p.

6. Larcher V. Plant ecology M.: Mir 1978, 283-324c.

7. Maksimov N. A. Selected works on drought resistance and winter hardiness of plants M.: Publishing House AN-USSR.-1952 vol. 1-2

8. Polevoy V.V. Plant Physiology 1978 414-424s.

9. Selyaninov G. T. On the methodology of agricultural climatology. Works on agriculture meteorology, 1930, v. 22

10. Tikhomirov B. A. Essays on the biology of plants in the Arctic. L., Publishing House of the USSR Academy of Sciences, 1963

11. Tumanov I.I. Causes of plant death in the cold season and measures to prevent it. M., Knowledge, 1955

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Summer

First, let's look at the option without air conditioning. It would seem that room temperature in summer is close to open ground conditions. But it turns out that in reality the temperature in the apartment is slightly higher than the street temperature - we close the windows when leaving for work, the glass creates a greenhouse effect, there is not the slightest draft... But the greenhouse effect is against the background of dry air, and not high humidity. In the evening, when the plants go into a state of half-sleep, we give them fan blowing.

The air conditioner in the house also dries out the air somewhat, so spray the plants in the morning and evening, and place cups of water. You can get a decorative mini-waterfall. The air flow from the air conditioner should not vibrate the leaves of plants - a draft is poorly tolerated not only by decorative plants. indoor plants, but also herbs.

Solution: place cups of water between the pots. Moisture will help plants survive the summer heat. Shade the plants, for example, by attaching sheets of white paper or reflective film to the glass (if the windows face the south and southeast).

You can help the plant adapt to the heat a little with the help of phytohormones. For example, Epin or Zircon. These drugs increase the resistance of plants to dryness, heat, soil changes and lack of light.

Autumn and winter

Since October, most of our perennial species spices gradually go into a dormant stage, wither and wait for the moment when we find a cool, dark place for them. Such conditions are needed, for example, for oregano (oregano). This could be a glazed loggia, the temperature in which in winter does not drop below 5 degrees. Wintering herbs in an apartment deserves a separate article.

In winter, the temperature in our average apartment did not rise above 18 degrees. The windowsill on which the plants stand heats up more, drying out the soil.

Solution: I do this - I roll up a bath towel and place it between the windowsill and the radiator, thereby dissipating the heat. However, this is true for plants that do not go dormant, such as rosemary and thyme. Although they should be sent to a cooler (10-12 degrees), but bright place.

Spring

In the spring, our herbs enter a phase of intensive growth, we replant the plants - it is during this period that the plants need a little more warmth. Spring does not always come according to the calendar, so a little reheating may be necessary.

Solution: I practice warm watering, about 30 degrees.

Ventilate rooms in the evenings, regardless of the time of year. This is useful not only for plants, but also for us.