The influence of temperature on the vital activity of plants. Cheat sheet: The effect of high temperatures on plants. Plants requiring cold storage

Life and development indoor plants depends on many factors, the main one being temperature. The influence of temperature on plants can be both positive and extremely negative. Of course, it all depends on the type of plant and its preferences in the wild, but some species lose their original habits and fully adapt to apartment conditions.

Each type of plant needs a different amount of heat, some of them can tolerate deviations from acceptable temperature conditions while others suffer and are hindered in development.

An important factor is not only the amount of heat received by the plant, but also the duration of the heat exposure. At different stages of a plant's life, the amount of heat required often varies, so at the stage of active growth, most plants need a warm atmosphere, but when the plant goes into a dormant period, it is recommended to reduce the amount of heat received.

Comfortable temperature for each plant is determined based on the values of the maximum and minimum temperature at which the plant develops normally or feels comfortable at different stages of life. A temperature drop below acceptable values, as a rule, leads to the attenuation of all processes, inhibition of development and weakening of the photosynthesis process. An increase, on the contrary, activates and accelerates these processes.

In the cold season, the effect of temperature on plants is slightly different. Plants will be comfortable at lower temperatures, this is due to the fact that most plants go into a dormant phase during this period. At this time, the growth process slows down or stops altogether, the plant seems to be sleeping, waiting for more favorable conditions. Therefore, there is no reason to maintain a high temperature during this period, the need for heat by plants is much less than in summer.

able to withstand sudden changes in temperature
thermophilic
cool content lovers

The first group includes aspidistra, aucuba, clivia, monstera, ficuses, tradescantia and even some types of palm trees. Fans of warm conditions in winter include orchids, coleus, and others. These plants suffer from a lack of heat and can die, so their maintenance must be approached responsibly. The third group includes jasmine, cyclamen, boxwood and others. These plants will feel good in cool rooms at average temperatures of 8-12 degrees.

Usually representatives of the third group cause difficulties, because in the cold season it is problematic to create cool conditions. Yes, yes, no matter how ridiculous it may sound, but it is exactly so. People themselves are by nature thermophilic, and not many of them want to live in cool conditions for the sake of indoor plants, and besides, heating sometimes fries, so at least open the windows for plowing =)

To create cool conditions, you can put such plants on window sills, but in this case it is necessary to protect them from the heat of heating systems, for example, by fencing protective screen or turn the heat down a little.

If the effect of temperature on plants can be different, then sharp temperature fluctuations will definitely have a negative effect. This often happens, especially in winter. Rapid changes in temperature can adversely affect the root system of the plant, overcool the roots and leaves, as a result of which the plant can become sick. Most of all, plants standing on window sills are subject to such drops, where they are in the position “between the hammer and the anvil”. On the one hand, heat from the battery presses, and on the other hand, cold when airing and frozen windows.

Of course, tropical plants are most sensitive to drops, but cacti endure even strong jumps. By nature, their cacti are in conditions where day and night temperatures can differ by tens of degrees.

When airing rooms, plants must be protected, especially those that are on the windowsill. For this purpose, you can use a sheet of cardboard, if there is nothing to protect the plants - it is better to remove them away from the window for the time of airing.

The article gives general information Naturally, the effect of temperature on plants of specific species can vary greatly. It is better to get acquainted with the recommended temperatures for individual plant species in the catalog.

The negative impact of cold depends on the range of temperature decrease and the duration of their exposure. Already non-extreme low temperatures adversely affect plants, because:

inhibit the main physiological processes (photosynthesis, transpiration, water exchange, etc.),
reduce the energy efficiency of breathing,
change the functional activity of membranes,
lead to the predominance of hydrolytic reactions in the metabolism.

Externally, cold damage is accompanied by a loss of turgor by leaves and a change in their color due to the destruction of chlorophyll. The main reason damaging action low positive temperature on heat-loving plants - a violation of the functional activity of membranes due to the transition of saturated fatty acids from a liquid-crystalline state to a gel. As a result, on the one hand, the permeability of membranes for ions increases, and on the other hand, the activation energy of enzymes associated with the membrane increases. The rate of reactions catalyzed by membrane enzymes decreases faster after a phase transition than the rate of reactions associated with soluble enzymes. All this leads to unfavorable changes in metabolism, a sharp increase in the amount of endogenous toxicants, and, with prolonged exposure to low temperatures, to the death of the plant.

It is found that the action low negative temperatures depends on the state of plants and, in particular, on the hydration of body tissues. Thus, dry seeds can tolerate temperatures as low as -196°C (liquid nitrogen temperature). This shows that the detrimental effect of low temperature is fundamentally different from the effect of high temperature, which causes direct protein coagulation.

The main damaging effect ice formation has an effect on the plant organism. In this case, ice can form as inside the cell and outside the cell. With a rapid decrease in temperature, the formation of ice occurs inside the cell (in the cytoplasm, vacuoles). With a gradual decrease in temperature, ice crystals are formed primarily in the intercellular spaces. The plasmalemma prevents the penetration of ice crystals into the cell. The contents of the cell are in a supercooled state. As a result of the initial formation of ice outside the cells, the water potential in the intercellular space becomes more negative compared to the water potential in the cell. There is a redistribution of water. The balance between the water content in the intercellular spaces and in the cell is achieved due to:

or the outflow of water from the cell,
or the formation of intracellular ice.

If the rate of water outflow from the cell corresponds to the rate of temperature decrease, then no intracellular ice is formed. However, the death of the cell and the organism as a whole can occur as a result of the fact that ice crystals formed in the intercellular spaces, drawing water from the cell, cause its dehydration and at the same time exert mechanical pressure on the cytoplasm, damaging cellular structures. This causes a number of consequences:

loss of turgor
increase in the concentration of cell sap,
a sharp decrease in cell volume,
shift of pH values in an unfavorable direction.

Plant resistance to low temperatures is divided into cold resistance and frost resistance.

Cold tolerance of plants- the ability of heat-loving plants to tolerate low positive temperatures. Protective value under the action of low positive temperatures on heat-loving plants has a number of adaptations. First of all, it is the maintenance membrane stability and ion leakage prevention. Resistant plants are distinguished by a greater proportion of unsaturated fatty acids in the composition of membrane phospholipids. This allows you to maintain the mobility of the membranes and protects against damage. In this regard, the enzymes acetyltransferase and desaturase play an important role. The latter lead to the formation of double bonds in saturated fatty acids.

Adaptive reactions to low positive temperatures are manifested in the ability to maintain metabolism when it decreases. This is achieved by a wider temperature range of enzymes, the synthesis of protective compounds. In resistant plants, the role of the pentose phosphate pathway of respiration increases, the efficiency of the antioxidant system increases, and stress proteins are synthesized. It has been shown that under the action of low positive temperatures, the synthesis of low molecular weight proteins is induced.

To increase cold resistance, pre-sowing soaking of seeds is used. The use of trace elements (Zn, Mn, Cu, B, Mo) is also effective. So, soaking seeds in solutions boric acid, zinc sulfate or copper sulfate increases the cold resistance of plants.

Frost resistance of plants- the ability of plants to tolerate negative temperatures.

Plant adaptations to negative temperatures . There are two types of adaptations to the action of negative temperatures:

avoidance of the damaging effect of the factor (passive adaptation),
increased survival (active adaptation).

Escape from the damaging effect of low temperatures is achieved, first of all, due to a short ontogeny - this care in time. At annual plants life cycle ends before freezing temperatures. These plants have time to give seeds before the onset of autumn cold weather.

Most perennials lose their above-ground organs and overwinter in the form of bulbs, tubers or rhizomes, well protected from frost by a layer of soil and snow - this is care in space from damaging effects of low temperatures.

hardening- this is a reversible physiological adaptation to adverse effects, occurring under the influence of certain external conditions, refers to active adaptation. The physiological nature of the process of hardening to negative temperatures was revealed thanks to the works of I.I. Tumanov and his schools.

As a result of the hardening process, the frost resistance of the body increases sharply. Not all plant organisms have the ability to harden, it depends on the type of plant, its origin. Plants of southern origin are not capable of hardening. In plants of northern latitudes, the process of hardening is confined only to certain stages of development.

Hardening of plants takes place in two phases:

First phase hardening takes place in the light at slightly lower positive temperatures (about 10 ° C during the day, about 2 ° C at night) and moderate humidity. In this phase, a further slowdown continues, and even a complete stop of growth processes.

Of particular importance in the development of plant resistance to frost in this phase is the accumulation of cryoprotective substances that perform a protective function: sucrose, monosaccharides, soluble proteins, etc. Accumulating in cells, sugars increase the concentration of cell sap, reduce water potential. The higher the concentration of the solution, the lower its freezing point, so the accumulation of sugars stabilizes cellular structures, in particular chloroplasts, so that they continue to function.

Second phase hardening proceeds with a further decrease in temperature (about 0 ° C) and does not require light. In this regard, for herbaceous plants, it can also occur under snow. In this phase, there is an outflow of water from the cells, as well as a restructuring of the protoplast structure. The neoformation of specific, dehydration-resistant proteins continues. Of great importance is the change in the intermolecular bonds of cytoplasmic proteins. When dehydration occurs under the influence of ice formation, the convergence of protein molecules occurs. The bonds between them break and are not restored in their previous form due to too strong convergence and deformation of protein molecules. In this regard, the presence of sulfhydryl and other hydrophilic groups, which contribute to the retention of water and prevent the convergence of protein molecules, is of great importance. The rearrangement of the cytoplasm contributes to an increase in its permeability to water. Due to the faster outflow of water, the risk of intracellular ice formation is reduced.

In relation to temperature, the following types of plants are distinguished:

1. Thermophiles, megathermal, heat-loving plants, the temperature optimum of which lies in the region of elevated temperatures.
2. Cryophiles, microthermal, cold-loving plants, the temperature optimum of which lies in the region of low temperatures.
3. Mesothermal plants are an intermediate group.

The endurance of plants to extreme temperatures characterizes their heat resistance and frost resistance. To the effect of temperature as a factor, land plants have developed a number of adaptations.

So, the plant protects from overheating:

1. Transpiration (evaporation of 1 g of water at 20 ° requires 500 kcal)
2. Shiny surface, dense pubescence, vertical arrangement narrow leaf blades (fescue, feather grass), the general reduction of the leaf surface - that is, all those devices that serve to weaken the influence of solar radiation.
3. Cork on the bark, air cavities on the root neck - adaptations characteristic of desert plants.
4. A kind of adaptation is the occupation by plants of certain ecological niches protected from overheating.
5. Experience of the hottest months in a state of suspended animation or in the form of seeds and underground organs.

Special adaptation to the effect of cold plants do not, but from the whole complex of adverse factors associated with it ( strong winds, the possibility of desiccation) the plant is protected by such morphological features as pubescence of the bud scales, tarring of the buds, a thickened cork layer, and a thick cuticle. A peculiar adaptation to the cold is observed in the highlands of Africa in lobelia rosette trees during the night cold, the rosettes of leaves close.

The following also help protect against the cold:

1. Small size, dwarfism, or nanism. For example, in dwarf birch and willow - Betula nana, Salix polaris.
2. Creeping forms - stlantsy.
3. Experience of the hottest months in a state of suspended animation or in the form of seeds or underground organs.
4. A special life form of cushion plants (in heather) is able to maintain the temperature in the thick of the branches 13 ° C higher than the ambient temperature.
5. Development contractile- contractile roots. In autumn, such roots dry out, shorten and press the wintering buds deep into the soil, which prevents the buoyant force of permafrost).

For plants of temperate regions, physiological methods of protection from the cold are more characteristic.

1. Decreased freezing point of cell sap (more soluble sugars, increased proportion of colloidally bound water). In general, plants in this regard are less adapted than insects.
2. Decrease in temperature optima of physiological processes. In arctic lichens, for example, photosynthesis is optimal at 5° and possible at -10°
3. Snow growth in the pre-spring period in blueberries, tulips and other ephemeroids.
4. Anabiosis- an extreme measure of plant protection - a state of rest, during which the plant is able to endure up to -200 ° C. In a state of winter dormancy, a phase of deep or organic dormancy is distinguished, when cut branches do not bloom in warmth, and a phase of forced dormancy at the end of winter. The signal for the onset of rest is the reduction of the day.

The limit of cold that plants can endure under natural conditions is given by the magnitude of the lowest possible temperatures on the globe. Where the lowest temperature is recorded (-90°C, Vostok station in Antarctica), there is no vegetation; and in areas where plants live, a temperature of -68 ° C was noted (Oymyakon in Yakutia, the region of taiga forests from larch - Larix dahurica).

The vegetation cover of vast areas of the globe (temperate and arctic regions, high mountains) is annually exposed to low temperatures for several months. In addition, in some areas and in warmer seasons, plants may experience short-term effects of low temperatures (night and morning frosts). Finally, there are habitats where all plant life takes place against a very low temperature background (Arctic snow and seaweeds, snow-nival vegetation in the highlands). It is not surprising that natural selection has developed in plants a number of protective adaptations to the adverse effects of cold.

In addition to the direct effect of low temperature on plants, other adverse effects also arise under the influence of cold. For example, compaction and cracking of frozen soil leads to rupture and mechanical damage to the roots, the formation of an ice crust on the soil surface impairs aeration and respiration of the roots. Under a thick and long-lasting snow cover at a temperature of about 0 ° C, winter “damping out”, depletion and death of plants is observed due to the consumption of reserve substances for respiration, fungal diseases (“snow mold”), etc., and in the case of excessive moistened soil for plants is also dangerous winter "wetting". In the tundra and northern taiga, the phenomenon of frosty “bulging” of plants is common, which is caused by uneven freezing and expansion of soil moisture. In this case, forces arise that push the plant out of the soil, as a result of which whole sods “bulge out”, the roots are exposed and broken, etc., up to the felling of small trees. Therefore, in addition to the actual cold resistance (or frost resistance) - the ability to endure the direct effect of low temperatures, there is also the winter hardiness of plants - the ability to endure all the above unfavorable winter conditions.

Particular attention should be paid to how low soil temperatures affect plants. Cold soils in combination with a moderately warm regime of the air environment of plants (and sometimes with significant heating of the above-ground parts of plants) is a frequent phenomenon. These are the living conditions of plants in swamps and swampy meadows with heavy soils, in some tundra and. high-mountain habitats and in vast areas of permafrost (about 20% of the entire land mass), where only a shallow, so-called "active" layer of soil thaws during the growing season. Under conditions of low soil temperatures after snowmelt (0-10°C), a significant part of the vegetation of early spring forest plants - "snowdrops" passes. Finally, short-term periods of a sharp discrepancy between cold soils and warm air experience in early spring many temperate plants (including tree species).

Even in the last century, the German physiologist J. Sachs showed that when the soil is cooled to near-zero temperatures (covering the pot with ice), even heavily watered plants can wilt, since at low temperatures the roots are not able to intensively absorb water. On this basis, an opinion has spread in ecology about the "physiological dryness" of habitats with cold soils (that is, the inaccessibility of moisture to plants with its physical abundance). At the same time, they overlooked the fact that Sachs and other physiologists carried out their experiments with rather heat-loving plants (cucumbers, pumpkins, lettuce, etc.) and that in natural cold habitats, plants for which low soil temperatures serve as a natural background may react to them. quite differently. Indeed, modern studies have shown that in most plants of the tundra, swamps, and early spring forest ephemeroids, there are no oppression phenomena (difficulty in absorbing water, disturbances in the water regime, etc.) that could be caused by the “physiological dryness” of cold soils. The same has been shown for many plants in permafrost regions. At the same time, one cannot completely deny the depressing effect of low temperatures on the absorption of moisture and other aspects of the vital activity of the roots (respiration, growth, etc.), as well as on the activity of soil microflora. It is undoubtedly important in a complex of difficult conditions for plant life in cold habitats. "Physiological dryness", "physiological drought" due to low soil temperatures are possible in the life of plants in the most difficult conditions, for example, when growing heat-loving plants on cold soils or in early spring for tree species, when still non-leafy branches are very hot (up to 30-35 °C) and increase the loss of moisture, and the intensive work of the root systems has not yet begun.

Plants do not have any special morphological adaptations that protect against cold; rather, we can talk about protection from the whole complex of adverse conditions in cold habitats, including strong winds, the possibility of drying out, etc. In plants of cold regions (or those enduring cold winters ) often there are such protective morphological features as pubescence of bud scales, winter tarring of buds (in conifers), thickened cork layer, thick cuticle, pubescence of leaves, etc. However, their protective effect would make sense only to preserve the own heat of homeothermic organisms, for plants, these features, although they contribute to thermoregulation (reduction of radiation), are mainly important as protection against desiccation. IN flora There is interesting examples adaptations aimed at maintaining (albeit short-term) heat in certain parts of the plant. In the highlands of East Africa and South America, giant "rosette" trees from the genera Senecio, Lobelia, Espeletia and others from frequent night frosts, there is such protection: at night, the leaves of the rosette close, protecting the most vulnerable parts - the growing tops. In some species, the leaves are pubescent on the outside, in others, the water secreted by the plant accumulates in the outlet; at night, only the surface layer freezes, and the growth cones are protected from frost in a kind of “bath”.

Among the morphological adaptations of plants to life in cold habitats, small size and special forms of growth. Not only many herbaceous perennials, but also shrubs and shrubs of the polar and high mountain regions have a height of no more than a few centimeters, internodes are very close together, very small leaves(the phenomenon of nanism or dwarfism). In addition to the well-known example - dwarf birch (Betula dad), can be called dwarf willows (Sahx polaris, S. arctica, S. herbacea) and many others. Usually the height of these plants corresponds to the depth of the snow cover under which the plants hibernate, since all parts protruding above the snow die from freezing and drying. Obviously, in the formation of dwarf forms in cold habitats, a significant role is played by the poverty of soil nutrition as a result of the suppression of microbial activity, and the inhibition of photosynthesis by low temperatures. But regardless of the method of formation, dwarf forms give a certain advantage to plants in adapting to low temperatures: they are located in the near-soil ecological microniche, which is warmest in summer, and in winter they are well protected by snow cover and receive an additional (albeit small) heat influx from the depth of the soil.

Another adaptive feature of the growth form is the transition of relatively large plants (shrubs and even trees) from orthotropic (vertical) to plagiotropic (horizontal) growth and the formation of creeping forms - dwarfs, dwarfs, dwarfs. Such forms are able to form cedar dwarf (Pinus pumila), juniper (Juniperus sibirica, J. communis, J. turkestanica), mountain ash, etc. The branches of the stlanets are spread out on the ground and rise no higher than the usual depth of the snow cover. Sometimes this is the result of the death of the trunk and the growth of the lower branches (for example, in spruce), sometimes it is the growth of a tree, as it were, “lying on its side” with a plagiotropic, rooted in many places trunk and rising branches (cedar elfin). Interesting feature some woody and shrubby dwarfs - the constant death of the old part of the trunk and the growth of the "top", as a result of which it is difficult to determine the age of the individual.

Dwarfs are common in high-mountainous and polar regions, in conditions that tree species can no longer withstand (for example, on the upper border of the forest). Peculiar "dwarf" forms in extreme conditions are also found in shrubs, and even in lichen species, which usually have upright bushy growth: on the rocks of Antarctica they form creeping thalli,

Depending on the conditions, modifications of the growth of the same species are possible. But there are species that have completely switched to the form of elfin, for example, mountain pine dwarf, growing in the Alps and Carpathians - Pinus mughus, designated as independent species from mountain pine - Pinus montana.

Among the growth forms that contribute to the survival of plants in cold habitats, there is another extremely peculiar one - cushion-shaped. The cushion plant form is formed as a result of increased branching and extremely slow growth of skeletal axes and shoots. Small xerophilous leaves and flowers are located on the periphery of the pillow. Fine earth, dust, small stones accumulate between individual branches. As a result, some types of cushion plants acquire greater compactness and extraordinary density: such plants can be walked on as if on solid ground. These are Silene acaulis. Gypsophila aretioides, Androsace helvetica, Acantholimon diapensioides. From a distance it is difficult to distinguish them from boulders. Less dense prickly pillows from childbirth Eurotia, Saxifraga.

Pillow plants come in different sizes (up to 1 m in diameter) and various shapes: hemispherical, flat, concave, sometimes quite bizarre shapes (in Australia and New Zealand they are called "plant sheep").

Thanks to their compact structure, cushion plants successfully resist cold winds. Their surface heats up in much the same way as the surface of the soil, and temperature fluctuations inside are less pronounced than in the environment. There have been cases of a significant increase in temperature inside the pillow; for example, in the most common species of the highlands of the Central Tien Shan Dryadanthe tetrandra at an air temperature of 10°C inside the pillow, the temperature reached 23°C due to the accumulation of heat in this kind of "greenhouse". Due to their slow growth, cushion plants are comparable in longevity to trees. So, in the Pamirs a pillow Acantholimon hedini with a diameter of 3 cm had an age of 10-12 years, with 10 cm - 30-35 years, and the age of large pillows reached more than one hundred years.

Within the general form of cushion plants, there is ecological diversity: for example, in the mountains surrounding the Mediterranean Sea, less compact xerophilic “thorny cushions” are common in structure, which are not found high in the mountains, as they are not resistant to cold, but are very resistant to drought. The loose structure of the pillow here turns out to be more beneficial for the plant than the compact one, since in conditions of summer drought and strong insolation it reduces the risk of overheating of its surface. The surface temperature of Mediterranean pillows is usually lower than the air temperature due to strong transpiration, and a special microclimate is created inside the pillow; for example, the humidity of the air is kept at 70-80% when the humidity of the outside air is 30%. Thus, here the shape of the pillow is an adaptation to a completely different set of factors, hence its different “design”.

Among other features of growth that help plants overcome the effects of cold, one should also mention various adaptations aimed at deepening the wintering parts of plants into the soil. This is the development of contractile (contractile) roots - thick and fleshy, with highly developed mechanical tissue. In autumn, they dry out and greatly shorten in length (which is clearly visible by the transverse wrinkling), while forces arise that draw wintering buds of renewal, bulbs, roots, and rhizomes into the soil.

Contractile roots are found in many plants in the highlands, tundra, and other cold habitats. They allow, in particular, to successfully resist the frosty bulging of plants from the soil. In the latter case, they not only draw in the renewal bud, but also orient it perpendicular to the surface if the plant is knocked down. The depth of retraction by contractile roots varies from a centimeter to several tens of centimeters, depending on the characteristics of the plant and the mechanical composition of the soil.

Adaptive shape-shifting as a defense against cold is a phenomenon limited mainly to cold areas. Meanwhile, the plants of more temperate regions also experience the effect of cold. Physiological methods of protection are much more universal. They are aimed primarily at lowering the freezing point of cell sap, preventing water from freezing, etc. Hence such features of cold-resistant plants as an increase in the concentration of cell sap, mainly due to soluble carbohydrates. It is known that during the autumn increase in cold resistance (“hardening”), starch turns into soluble sugars. Another feature of cold-resistant plants is an increase in the proportion of colloidally bound water in the total water reserve.

With a slow decrease in temperature, plants can tolerate cooling below the freezing point of cell sap in a state of hypothermia (without ice formation). As experiments show, the level of hypothermia and freezing points is closely related to the temperature conditions of habitat. However, in plants, the state of hypothermia is possible only with a slight cold (a few degrees below zero). This way of adaptation is much more effective in other poikilotherms. insect organisms, in which glycerin, trehalose and other protective substances play the role of antifreezes (openly hibernating insects can tolerate hypothermia of cell sap without freezing to -30 ° C).

Many plants are able to remain viable even in a frozen state. There are species that freeze in autumn in the flowering phase and continue to bloom after thawing in spring (wood louse - stellaria media, daisy- bellis perennis, arctic horseradish - Cochlearia fenestrata and etc.). Early spring forest ephemeroids ("snowdrops") during a short growing season repeatedly endure spring night frosts: flowers and leaves freeze to a vitreous-brittle state and become covered with hoarfrost, but already 2-3 hours after sunrise they thaw and return to their normal state. The ability of mosses and lichens to endure prolonged freezing in winter in a state of suspended animation is well known. In one of the experiments, lichen Cladonia frozen at -15°C for 110 weeks (more than two years!).

After thawing, the lichen turned out to be alive and quite viable; photosynthesis and growth resumed in it. Obviously, in lichens in extremely cold conditions of existence, the periods of such suspended animation are very long, and growth and active life activity are carried out only in short favorable periods (and not every year). Such a frequent interruption of active life for long periods, apparently, explains the colossal age of many lichens, determined by the radiocarbon method (up to 1300 years for Rhizocagon geographicum and the Alps, up to 4500 years in lichens in West Greenland).

Anabiosis is an "extreme measure" in the fight of a plant against cold, leading to a suspension of vital processes and a sharp decrease in productivity. Much more important in the adaptation of plants to cold is the possibility of maintaining normal vital activity by reducing the temperature optimums of physiological processes and the lower temperature limits at which these processes are possible. As can be seen from the example of optimal temperatures for photosynthesis and its lower temperature thresholds, these phenomena are well expressed in plants of cold habitats. So, in Alpine and Antarctic lichens for photosynthesis, the optimum temperature is about 5 ° C; noticeable photosynthesis can be detected in them even at -10°C. At relatively low temperatures, the optimum of photosynthesis lies in arctic plants, alpine species, and early spring ephemeroids. In winter, at low temperatures, many coniferous tree species are capable of photosynthesis. In the same species, the temperature optima of photosynthesis are associated with changes in conditions: for example, in alpine and arctic populations of herbaceous perennials - Ohu ria digyna, Thalictrum alpinum and other species, they are lower than those of the plains. Indicative in this respect is the seasonal shift of the optimum as the temperature rises from spring to summer and decreases from summer to autumn and winter.

At low temperatures, it is extremely important for plants to maintain a sufficient level of respiration - the energy basis for growth and repair of possible cold damage. On the example of a number of plants of the Pamir highlands, it was shown that under these conditions, rather intensive respiration is maintained after the action of a temperature of -6 to -10°C.

Another example of the resistance of physiological processes to cold weather is winter and pre-spring snowy growth in plants of the tundra, high mountains and other cold habitats with a short growing season due to advance preparation. This phenomenon is extremely pronounced in the ephemeroids of forest-steppe oak forests (scilla - Scilla sibirica, corydalis - Corydalis halleri, goose onion - Gagea lutea, clean - Ficariaverna and others), in which, already at the beginning of winter, the growth of shoots with buds formed inside begins (first in the frozen soil, and then above the soil, inside the snow cover. The formation of generative organs does not stop in them in winter. As the snowmelt approaches, the speed of the snow growth noticeably increases.At the time of the early “pre-spring”, when the forest seems still completely lifeless, thousands of sprouts of blueberries and goose onions already rise under the snow cover above the soil, reaching 2-7 cm in height by this time and ready to begin flowering as soon as the snow melts The formation of chlorophyll in early spring ephemeroids also begins at low temperatures of the order of 0°C, even under snow.

Ecological differences in plant cold tolerance

In ecology and ecological physiology, the ability of a plant to tolerate low temperatures under experimental conditions for a certain period is used as one of the indicators of cold resistance. A lot of data has been accumulated that makes it possible to compare plants of habitats with different temperature conditions. However, these data are not always strictly comparable, since the temperature that a plant can tolerate, among other reasons, also depends on the duration of its action (for example, a moderately heat-loving plant can tolerate a slight cold of the order of -3-5 ° C for several hours, but that however, the temperature can be disastrous if it lasts for several days).

As can be seen from the following data and, the cold resistance of plants is very different and depends on the conditions in which they live.

One of the extreme examples of cold resistance is the so-called "cryoplankton". These are snow algae that live in the surface layers of snow and ice and cause its coloring during mass reproduction (“red snow”, “green snow”, etc.). In active phases, they develop at 0°C (in summer on the thawed surface of snow and ice). Limits of resistance to low temperatures from -36°С Chlamydomonas nivalis up to -40, -60°C Pediastrutn boryanum, Hormidium flaccidum. The cold resistance of the phytoplankton of the polar seas, which often hibernates in the ice crust, is just as great.

Alpine dwarf shrubs are distinguished by great cold resistance - Rhododendron ferrugineum, Erica carnea and others (-28, -36°С), coniferous tree species: for example, for pine Pinus strobus in the Tyrolean Alps, a record temperature was noted in the experiments: -78 ° С.

Very little cold resistance in plants of tropical and subtropical regions, where they do not experience the effects of low temperatures (with the exception of high mountains). So, for algae of tropical seas (especially shallow water areas), the lower temperature limit lies in the range of 5-14 ° C (recall that for algae of the Arctic seas, the upper limit is 16 ° C). Tropical tree species saplings die at 3-5°C. In many tropical thermophilic plants, such as ornamental greenhouse species from the genera Gloxinia, Coleus, Achimenes etc., lowering the temperature to several degrees above zero causes the phenomenon of "cold": in the absence of visible damage, growth stops after a while, leaves fall, plants wither, and then die. This phenomenon is also known for heat-loving cultivated plants (cucumbers, tomatoes, beans).

Very low resistance to cold in thermophilic mold fungi from the genera Mucor, Thermoascus, Anixia and others. They die in three days at a temperature of 5-6°C, and even a temperature of 15-17°C cannot endure for longer than 15-20 days.

Depending on the degree and specific nature of cold resistance, the following groups of plants can be distinguished.

Non-cold-resistant plants

This group includes all those plants that are already seriously damaged at temperatures above freezing: warm sea algae, some fungi and many leafy plants of tropical rainforests.

non-hardy plants

Although these plants tolerate low temperatures, they freeze out as soon as ice begins to form in the tissues. Non-hardy plants are only protected from damage by antifreeze agents. In the colder season, they have an increased concentration of osmotically active substances in the cell sap and protoplasm, as well as hypothermia, which prevents or slows down the formation of ice at temperatures down to about -7 ° C, and with constant supercooling even to lower temperatures. During the growing season, all leafy plants are not frost-resistant. Throughout the year, deep-sea algae, cold seas and some freshwater algae, tropical and subtropical woody plants and different kinds from warm temperate regions.

Ice resistant plants

In the cold season, these plants tolerate extracellular freezing of water and the dehydration associated with it. Some freshwater and intertidal algae, terrestrial algae, mosses of all climatic zones (even tropical) and perennial terrestrial plants of areas with cold winters are becoming resistant to ice formation. Some algae, many lichens, and various woody plants are capable of hardening extremely strongly; then they remain undamaged even after prolonged severe frosts, and they can be cooled even to the temperature of liquid nitrogen.

The temperature of the soil or artificial nutrient medium is of great importance when growing plants. Both high and low temperatures are unfavorable for the life of the root. At low temperatures, the respiration of the roots is weakened, as a result of which the absorption of water and nutrient salts decreases. This leads to wilting and stunting of the plant.

Cucumbers are especially sensitive to a decrease in temperature - a decrease in temperature to 5 ° C destroys cucumber seedlings. The leaves of mature plants at low temperature of the nutrient solution in sunny weather wilt and get burned. For this crop, the temperature of the nutrient solution should not be lowered below 12°C. Usually in winter time When growing plants in greenhouses, the nutrient solution stored in the tanks is at a low temperature and should be heated to at least ambient temperature. The most favorable temperature of the solution used for growing cucumbers should be considered 25-30°C, for tomatoes, onions and other plants - 22-25°C.

If in winter it is necessary to heat the substrate on which the cultivation takes place, then in summer, on the contrary, the plants may suffer due to its high temperature. Already at 38-40°C water absorption and nutrients stops, the plants wilt and may die. It is impossible to allow the heating of solutions and the substrate to such a temperature. The roots of young seedlings are especially affected by high temperatures. For many cultures, a temperature of 28-30 ° is already fatal.

If there is a danger of overheating, it is useful to wet the surface of the soil with water, the evaporation of which lowers the temperature. IN summer time in practice greenhouse farming spraying of glass with lime mortar is widely used, which scatters the direct rays of the sun and saves plants from overheating.

Sources

Growing plants without soil / V.A. Chesnokov, E.N. Bazyrina, T.M. Bushueva and N.L. Ilyinskaya - Leningrad: Leningrad University Press, 1960. - 170 p.