Transpiration in plants is the most important process in the physiology of the plant world.
Transpiration in plants is a natural process of water exchange between the plant world and atmospheric air. Research by scientists has shown that the daily amount of evaporated moisture significantly exceeds the volume of water contained in the plant. This phenomenon is of paramount importance in the life of any plant organism growing in greenhouse conditions or on open ground. From this publication you will learn what transpiration in plants is, get acquainted with the varieties and methods of regulating this process..
The life process of any plant is inextricably linked with the consumption of moisture. From the daily volume of the obtained water for photosynthesis and physiological needs, the plant needs only 10%. The remaining 90% is evaporated into the atmosphere.
Transpiration is the process of moving fluid through a plant organism and vaporizing it from the ground part of the plant. Leaves, stems, flowers, fruits, and the root system of a plant organism are involved in transpiration..
Why does a plant need to evaporate moisture? Transpiration allows the plant to receive nutrients and trace elements dissolved in water from the soil.
The mechanism of action is as follows:
- Being freed from excess moisture, negative pressure is created in the water-carrying tissues of plants..
- Depressurization “pulls” moisture from neighboring xylem cells, and so, along a chain, directly to the suction cells of the root system.
Through the evaporation process, plants naturally regulate their temperature, protecting themselves from overheating. It has been proven that the temperature of the transpiring sheet is lower than the non-evaporating moisture. The difference reaches 7 ° C.
Plants have two types of moisture exchange:
- through the stomata;
- through the cuticles.
To understand the principle of operation of this phenomenon, it is necessary to recall the structure of the leaf from the school course in biology..
The plant leaf consists of:
- Epidermal cells that form the main protective layer.
- Cuticle – waxy (outer) protective layer.
- Mesophyll or “pulp” – the main tissue located between the outer layers of the epidermis.
- Veins – “transport arteries” of the leaf, along which moisture saturated with nutrients moves.
- Estuaries – holes in the epidermis that control the gas exchange of the plant.
With stomatal transpiration, the process of evaporation occurs in two stages:
- The transition of moisture from the liquid phase to the vapor phase. Liquid water is located in the cell membranes. Steam is formed in the intercellular space.
- Release of gaseous moisture into the atmosphere through the mouth of the epidermis.
With stomatal moisture exchange, the plant can regulate the level of evaporation. Next, we will consider the mechanism of action of this process..
Cuticular transpiration regulates the evaporation of moisture from the leaf surface when the mouths are closed. The rate of evaporation of the liquid depends on the thickness of the cuticle and the age of the plant..
It is important to know that the level of oral transpiration is 80 to 90% of the evaporation volume of the entire leaf. That is why this mechanism is the main regulator of the intensity of evaporation in plants..
Leaf as an organ of transpiration
We have analyzed what transpiration is. Now we need to understand what role the leaf plays in this mechanism..
Due to the large evaporation area, the leaves are the main diffusing areas of the plant. The process of evaporation of moisture begins from the bottom of the leaf through the open mouths, through which oxygen and carbon dioxide are exchanged between the plant and the surrounding air..
The stomatal opening mechanism is as follows:
- Guard cells are located around the circumference of the orifices.
- With an increase in volume, they stretch the holes in the epidermis, increasing the opening of the stomata..
The reverse process occurs with a decrease in the volume of guard cells, the walls of which cease to affect the stomatal gaps.
Intensity of transpiration
The intensity of transpiration is the amount of moisture evaporated from dm2 of a plant per calculated unit of time. This parameter is regulated by the size of the opening of the stomatal gaps, which, in turn, depends on the amount of light falling on the plant. Next, consider how light affects the intensity of transpiration..
The deformation of epidermal cells occurs under the influence of photosynthesis, during which starch is converted into sugars.
- In the light, plants begin the process of photosynthesis. The pressure in the guard cells increases, which makes it possible to draw water from the neighboring cells of the epidermis. Cell volume increases, stomata open.
- In the evening and at night, sugars are converted into starch, during which the epidermal cells “pump out” moisture from the guard cells of the plant. Their volume decreases, the stomata close.
In addition to light, the intensity of transpiration is influenced by the wind and the physical characteristics of the air:
- The lower the level of humidity of the atmospheric air, the faster the evaporation of water, and hence the rate of moisture exchange.
- As the temperature rises, the elasticity of water vapor increases, which leads to a decrease in the humidity characteristics of the environment and an increase in the volume of evaporated water..
- Under the influence of wind, the rate of moisture evaporation increases significantly, thereby accelerating the transfer of moist air from the leaf surface, causing increased water exchange.
To determine this parameter, one should not forget about the level of soil moisture. If it is not enough, then there is a lack of it in the plant. Reducing the amount of moisture in the plant body automatically changes the rate of evaporation.
Diurnal variation of transpiration
During the day, the level of moisture evaporation in plants changes:
- At night, the process of water exchange between the plant and the surrounding air practically stops. This is due to the absence of the sun, the closure of the holes of the epidermis, a decrease in the temperature of the atmospheric air and an increase in its level of humidity..
- At dawn, the mouths open. The degree of their disclosure increases with a change in illumination, climatic and physical indicators of air masses.
- The maximum intensity of transpiration in plants is observed at noon, by 12-13 hours. This process is influenced by the intensity of sunlight..
- With insufficient humidity in the daytime, the intensity of water exchange may decrease. This mechanism allows the plant to significantly reduce moisture loss, protecting itself from wilting..
- With a decrease in solar insolation in the evening hours, the intensity of transpiration increases again.
The daily process of moisture exchange also depends on the type and age of plants, the region of growth, the layout of the leaves..
In cacti, the increase in transpiration occurs exclusively at night, when the mouths are fully open. In plants, the foliage of which is turned laterally to the horizon, this process begins immediately with the first rays of sunlight..