Plant growth is highly dependent on temperature and can occur from zero to 35°.

The growth rate at temperatures above 35-40° drops, and with a further increase it turns.

Different plants have different attitudes towards temperature. Some plants are thermophilic and require higher temperatures to grow. Other plants are more tolerant of low temperatures and sensitive to excessive increases.

Regulating temperature regime in combination with other living conditions, growth can be controlled, i.e., suspended or brought to an optimal level. It should be borne in mind that it is impossible to use heat to accelerate or slow down growth without providing the plant with light and moisture.

To quickly produce stocky plants, you need more light, heat and moisture (up to optimal sizes).

The effect of temperature on a plant is very often used in greenhouses. To accelerate growth, plants are provided with elevated temperatures from the early stages of development until flowering. This technique accelerates the growth and development of the plant, but it is not always taken into account that plants grown at a higher temperature turn out to be weaker than those developed at a lower temperature. Plants grown in greenhouses at higher temperatures quickly lose their decorative properties in residential areas.

When growing plants in greenhouses, you need to pay attention to this and not sell products that quickly die in the rooms.

An example of erroneous temperature effects on plants is the cultivation of summer seedlings at elevated temperatures. Seedlings are obtained by appearance good, but poorly adapted to endure the hardships of open ground (low life resistance).

If the plant finishes its growth earlier than planned, it is placed in a room with a low temperature to delay growth. If the plant is not squat, but somewhat elongated, it is placed in a cooler room at night. To make plants more decorative, you should always reduce the room temperature at night. A gradual and temporary decrease in temperature, repeated several times, increases the resistance of heat-loving plants to low temperatures.

Increasing the cold resistance of plants is achieved by sowing seeds directly into open ground. In this case, the seedlings can withstand frosts of 2-3°. Seedlings of many plants grown in greenhouses and greenhouses die in the soil at -1, -2°.

Increasing the resistance of plants to low temperatures can be achieved by breeding cold-resistant varieties, “cooling” seeds, etc.

Temperature conditions also affect the release of seeds from dormancy (stratification), as well as their subsequent germination. This mode is also important for passing the rest period. Plants that come from northern latitudes require organic rest. Without passing through rest at low temperatures they will not grow and develop well in the future. To speed up the passage of organic dormancy, you need to provide the plant with a low temperature.

If it is necessary to postpone the onset of dormancy or extend its period, the plant is created with conditions that are unfavorable for the passage of organic dormancy, that is, they are not given an appropriate low temperature.

If organic dormancy has passed, to retard growth or prolong forced dormancy, the plants are again placed in conditions of low temperatures.

An increase in temperature with forced rest reduces the latter.

To delay the germination of some tubers, bulbs and seeds, snow is used or trenches with frozen soil are used to contain them.

Seed curing in early spring at a temperature of 5-20°, especially in sunlight, ensures their ripening within 7-10 days; at temperatures around 0 this process occurs very slowly. Higher temperatures in August promote ripening of the bulbs.

To retard plant growth in open ground in the spring it is affected by trampling the snow and covering it with manure around the plant.

Air temperature also affects plant respiration, which becomes more intense at elevated temperatures.

In winter, when there is almost no accumulation of organic substances in insufficient light, it is necessary to reduce the respiration rate by providing the plant with a slightly lower temperature. This also applies to bulbs, tubers and rhizomes stored in winter.

The temperature of the soil or artificial growing medium has great importance when growing plants. Both high and low temperatures are unfavorable for the life of the root. At low temperatures, root respiration 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 low temperatures - a decrease in temperature to 5°C destroys cucumber seedlings. Leaves of adult plants at low temperature nutrient solution in sunny weather wither and get burned. For this crop, the temperature of the nutrient solution should not be reduced below 12°C. Usually in winter time When growing plants in greenhouses, the nutrient solution stored in tanks has a low temperature and should be heated to at least the 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, plants may suffer due to its high temperature. Already at 38-40°C, water absorption and nutrients stops, the plants wither and may die. Solutions and substrates should not be allowed to reach this temperature. The roots of young seedlings are especially affected by high temperatures. For many crops, a temperature of 28-30° is already destructive.

If there is a danger of overheating, it is useful to moisten the soil surface with water, the evaporation of which lowers the temperature. IN summer time in practice greenhouse farming Spraying glass with lime mortar is widely used, which disperses 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 Publishing House, 1960. - 170 p.

Effect of air temperature

The vital processes of each plant species are carried out under a certain thermal regime, which depends on the quality of the heat and the duration of its exposure.

Various plants need different quantities heat and have different abilities to tolerate deviations (both downward and upward) of temperature from the optimal.

Optimal temperature- the most favorable temperature for a certain type of plant at a certain stage of development.

The maximum and minimum temperatures that do not disrupt the normal development of plants determine the temperature limits permissible for their cultivation in appropriate conditions. A decrease in temperature leads to a slowdown in all processes, accompanied by a weakening of photosynthesis, inhibition of the formation of organic substances, respiration, and transpiration. An increase in temperature activates these processes.

It is noted that the intensity of photosynthesis increases with increasing temperature and reaches a maximum in the region of 15-20℃ for plants of temperate latitudes and 25-30℃ for tropical and subtropical plants. The daily temperature in autumn interiors almost never drops below 13℃. In winter it is between 15-21℃. In spring, temperature fluctuations increase. It reaches 18-25℃. In summer, the temperature remains relatively high throughout the day and ranges from 22-28℃. As you can see, the indoor air temperature is almost within the temperature range required for the photosynthesis process to occur throughout the year. Temperature is therefore not such a limiting factor in room conditions, as the lighting intensity.

IN winter period indoor pets feel fine with more low temperatures ah, because many of them are at rest, while in others the growth processes slow down or temporarily stop. Therefore, the need for heat is reduced compared to summer.

The influence of light on plant growth – photomorphogenesis. Effect of red and far-red light on plant growth

Photomorphogenesis- these are processes occurring in a plant under the influence of light of different spectral composition and intensity. In them, light acts not as a primary source of energy, but as signal means, regulating processes of plant growth and development. You can draw some analogy with street traffic light, automatically regulating traffic. Only for control, nature chose not “red - yellow - green”, but a different set of colors: “blue - red - far red”.

And the first manifestation of photomorphogenesis occurs at the moment of seed germination.
I already talked about the structure of the seed and the characteristics of germination in the article about seedlings. But details related to signal by the action of light. Let us fill this gap.

So, the seed woke up from hibernation and began to germinate, while being under a layer of soil, i.e. darkness. Let me note right away that small seeds, sown superficially and not sprinkled with anything, also germinate in darkness at night.
By the way, according to my observations, in general, all raasada standing in a bright place germinates at night and you can see mass shoots in the morning.
But let's return to our unfortunate hatched seed. The problem is that even having appeared on the surface of the soil, the sprout does not know about it and continues to grow actively, reaching for the light, for life, until it receives a special signal: stop, you don’t have to rush any further, you’re already free and will live. (It seems to me that people themselves did not invent a red brake light for drivers, but stole it from nature...:-).
And it receives such signal not from air, not from moisture, not from mechanical impact, but from short-term light radiation containing red part of the spectrum.
And before receiving such a signal, the seedling is in the so-called etiolated condition. In which it has a pale appearance and a hooked, bent shape. The hook is an exposed epicotyl or hypocotyl, needed to protect the bud (growth point) when pushing through thorns to the stars, and it will remain if growth continues in the dark and the plant remains in this etiolated state.

Germination

Light plays an extremely important role in plant development. Changes in plant morphology under the influence of light radiation are called photomorphogenesis. After the seed germinates through the soil, the first rays of the sun cause radical changes in the new plant.

It is known that under the influence of red light the process of seed germination is activated, and under the influence of far-red light it is suppressed. Blue light also inhibits germination. This reaction is typical for species with small seeds, since small seeds do not have a sufficient supply of nutrients to ensure growth in the dark while passing through the soil. Small seeds germinate only when exposed to red light transmitted thin layer earth, while only short-term irradiation is enough - 5-10 minutes per day. An increase in the thickness of the soil layer leads to an enrichment of the spectrum with far-red light, which suppresses seed germination. In plant species with large seeds containing a sufficient supply of nutrients, light is not required to induce germination.

Normally, a root first sprouts from a seed, and then a shoot appears. After this, as the shoot grows (usually under the influence of light), secondary roots and shoots develop. This coordinated progression is an early manifestation of the phenomenon of coupled growth, where root development influences shoot growth and vice versa. To a greater extent, these processes are controlled by hormones.

In the absence of light, the sprout remains in the so-called etiolated state, and has a pale appearance and a hooked shape. The hook is an exposed epicotyl or hypocotyl that is needed to protect the growing point during germination through the soil, and it will remain if growth continues in the dark.

Red light

Why this happens - a little more theory. It turns out that, in addition to chlorophyll, in any plant there is another wonderful pigment, which has a name - phytochrome. (A pigment is a protein that has selective sensitivity to a certain part of the spectrum white light).
Peculiarity phytochrome is that it can take two forms With different properties under influence red light (660 nm) and distant red light (730 nm), i.e. he has the ability to phototransformation. Moreover, alternating short-term illumination with one or another red light is similar to manipulating any switch that has the “ON-OFF” position, i.e. The result of the last impact is always preserved.
This property of phytochrome ensures monitoring of the time of day (morning-evening), controlling frequency life activity of the plant. Moreover, love of light or shade tolerance of a particular plant also depends on the characteristics of the phytochromes it contains. And finally, the most important thing - flowering plants are also controlled... phytochrome! But more on that next time.

In the meantime, let's return to our seedling (why is it so unlucky...) Phytochrome, unlike chlorophyll, is found not only in leaves, but also in seed. Participation of phytochrome in the process of seed germination for some plant species are as follows: simply red light stimulates seed germination processes, and far red - suppresses seed germination. (It is possible that this is why the seeds germinate at night). Although this is not a pattern for everyone plants. But in any case, the red spectrum is more useful (it stimulates) than the far red spectrum, which suppresses the activity of life processes.

But let’s assume that our seed was lucky and it sprouted, appearing on the surface in an etiolated form. Now that's enough short-term lighting the seedling to start the process deetiolation: the growth rate of the stem decreases, the hook straightens, chlorophyll synthesis begins, the cotyledons begin to turn green.
And all this, thanks red to the world In solar daylight there are more ordinary red rays than far red rays, so the plant is highly active during the day, and at night it becomes inactive.

How can one distinguish between these two close parts of the spectrum “by eye” for a source of artificial lighting? If we remember that the red area borders on the infrared, i.e. thermal radiation, then we can assume that the warmer the radiation “feels to the touch”, the more infrared rays it contains, and therefore far red Sveta. Place your hand under a regular incandescent light bulb or fluorescent lamp daylight- and you will feel the difference.

Plant growth is possible in a relatively wide range of temperatures and is determined by the geographical origin of the species. The temperature requirements of a plant change with age and are different for individual plant organs (leaves, roots, fruit elements, etc.). For the growth of most agricultural plants in Russia, the lower temperature limit corresponds to the freezing temperature of cell sap (about -1...-3 ° C), and the upper limit corresponds to the coagulation of protoplasmic proteins (about 60 ° C). Let us remember that temperature affects the biochemical processes of respiration, photosynthesis and other metabolic systems of plants, and graphs of the dependence of plant growth and enzyme activity on temperature are similar in shape (bell-shaped curve).

Temperature optimum for growth. The emergence of seedlings requires a higher temperature than for seed germination (Table 22).

22. Requirement of field crop seeds for biologically minimum temperatures (according to V.N. Stepanov)

Temperature, "C

seed germination 1st emergence

Mustard, hemp, camelina 0-1 2-3

Rye, wheat, barley, oats, 1-2 4-5

peas, vetch, lentils, china

Flax, buckwheat, lupine, beans, 3-4 5-6

noug, beets, safflower

Sunflower, perilla 5-6 7-8

Corn, millet, soybeans 8-10 10-11

Beans, castor beans, sorghum 10-12 12-15

X-wolfwort, rice, sesame 12-14 14-15

When analyzing plant growth, three cardinal temperature points are distinguished: minimum (growth is just beginning), optimal (most favorable for growth) and maximum temperature (growth stops).

There are plants that are love-loving - with minimum temperatures for growth of more than 10 "C and optimal 30-35 "C (corn, cucumber, melon, pumpkin), cold-resistant - with minimum temperatures for growth within 0-5 "C and optimal 25-31 " WITH. Maximum temperatures for most plants are 37-44 "C, for southern ones 44-50" C. With an increase in temperature by 10 °C in the zone of optimal values, the growth rate increases by 2-3 times. Increasing the temperature above the optimum slows down growth and shortens its period. The optimal temperature for the growth of root systems is lower than for above-ground organs. The optimum for growth is higher than for photosynthesis.

It can be assumed that at high temperatures there is a lack of ATP and NADPH, necessary for reduction processes, which causes growth inhibition. Temperatures that are optimal for growth may be unfavorable for plant development. The optimum for growth changes throughout the growing season and during the day, which is explained by the need for temperature changes fixed in the plant genome, which took place in the historical homeland of plants. Many plants grow more intensively at night.

Thermoperiodism. The growth of many plants is favored by changes in temperature during the day: increased during the day and decreased at night. So, for tomato plants, the optimal temperature is 26 °C during the day, and 17-19 °C at night. F. Vent (1957) called this phenomenon thermoperiodism. Thermal periods! - the plant’s reaction) to periodic changes in high and low temperatures, expressed in changes in growth processes and development! (M. *. Chailakhyan, 1982). There are daily and seasonal thermal periods. For tropical plants, the difference between day and night temperatures is 3-6 ° C, for plants in the temperate zone - 5-7 "C. This is important to consider when growing plants in the field, greenhouses and phytotrons, zoning crops and varieties of agricultural plants.

The alternation of high and low temperatures serves as a regulator of the internal clock of plants, as in photope1_iodism. Relatively low night temperatures increase the yield of potatoes (F. Vent. 1959), the sugar content of sugar beet roots, and accelerate the growth of the root system and lateral shoots of tomato plants (N. I. Yakushkin, 1980). Low temperatures may increase the activity of enzymes that hydrolyze starch in leaves, and the resulting soluble forms of carbohydrates move to the roots and side shoots.

Plants vary in their ability to tolerate elevated temperatures. Most plants begin to suffer at temperatures of 35-40°C. Dehydrated organs tolerate elevated temperatures better: seeds up to 120°C, pollen up to 70°C. However, there are higher plants, mainly desert plants (for example, succulents), that can tolerate temperatures up to 60°C. Some algae, fungi and bacteria can tolerate even higher temperatures. The most thermophilic microorganisms (bacteria, some algae) that live in hot springs and volcano craters are able to withstand temperatures up to 100°C.

The temperature of transpiring leaves is lower than air temperature. Typically, plants reduce their temperature through transpiration and thus avoid overheating. Water deficiency, which occurs when there is not enough water, increases the adverse effects elevated temperatures. High temperature has a detrimental effect on organisms, which causes damage to membranes and proteins. Different enzyme proteins denature at different temperatures. However, even partial denaturation of some of the most thermolabile enzymes leads to disruption of the coordination of metabolic processes. Soluble nitrogenous compounds and other toxic metabolic intermediates accumulate, resulting in cell death.

The immediate response to temperature influence is change in membrane fluidity. Under the influence of high temperature, the amount of unsaturated phospholipids in membranes increases. As a result, the composition and structure of the membrane changes and, as a consequence, there is an increase in membrane permeability and the release of water-soluble substances from the cell. Increased fluidity of membrane lipids at high temperatures may be accompanied by:

• loss of activity of membrane-associated enzymes,
• disruption of electron transporters.

Photochemical reactions and photophosphorylation largely depend on the state of lipids in chloroplast thylakoids. High temperatures inhibit both photosynthesis and respiration. The conjugacy of energy processes decreases. Particularly sensitive to elevated temperatures photosynthesis. Depression of this process usually begins already at 35-40°C. It should be noted that at elevated temperatures the activity of phytohormones decreases. The activity of gibberellins drops sharply, which is one of the reasons for the inhibition of growth processes.

Organisms, depending on their temperature optimum, can be divided into:

• thermophilic (above 50°C),
• heat-loving (25-50°C),
• moderately thermophilic (15-25°C),
• cold-loving (5-15°C).

There are no thermophilic organisms among higher plants.

Plant resistance to high temperatures called heat resistance or thermotolerance. Elevated temperatures are especially dangerous for plants in strong light conditions. There is a certain connection between the living conditions of plants and their heat resistance. The drier the habitat and the higher the air temperature, the greater the heat resistance of the organism.

According to heat resistance, plants can be divided into 3 groups:

1) heat-resistant - mainly lower plants, for example, thermophilic bacteria and blue-green algae. This group of organisms is able to withstand temperature increases up to 75-90°C;

2) heat-tolerant - plants of dry habitats: succulents (withstand temperature increases up to 60°C) and xerophytes (up to 54°C);

3) non-heat-resistant – mesophytes and aquatic plants. Mesophytes of sunny habitats can tolerate +40-47°C, shaded habitats - approximately +40-42°C; aquatic plants, except blue-green algae, can withstand temperature increases up to 38-42°C.

Plant adaptation to high temperatures. In the process of evolution, they were formed and consolidated various mechanisms adaptations that make the plant more resistant to high temperatures. The development of such mechanisms went in several directions:

• reduction of overheating due to transpiration;
• protection from thermal damage (leaf pubescence, thick cuticle);
• stabilization of metabolic processes (more rigid membrane structure, low water content in the cell);
• high intensity of photosynthesis and respiration.

In cases where the damaging effect of high temperature exceeds the protective capabilities of morpho-anatomical and physiological adaptations, the following protection mechanism is activated: so-called heat shock proteins (HSPs). HSP is the last “line of defense” of a living cell, which is launched in response to the damaging effects of high temperatures. They were discovered in 1962 in Drosophila, then in humans, then in plants (1980) and microorganisms. HSPs help the cell survive under the influence of a temperature stressor and restore physiological processes after its cessation. HSPs are formed as a result of the expression of certain genes. Some of these HSPs are synthesized not only at elevated temperatures, but also under other stress factors, for example, lack of water, low temperatures, and exposure to salts.

To increase resistance to high temperatures, various hardening methods. Thus, alternating the action of elevated temperatures and normal conditions makes it possible to obtain more heat-resistant plants. A similar effect is observed after keeping wheat seeds for 8 hours with a gradual increase in temperature from 20 to 50°C. Increased heat resistance is also achieved by treating seeds with calcium chloride, zinc sulfate, and boric acid.