The process of spending water in a plant body is based on evaporation. However, it is complicated by some anatomical and physiological characteristics of cultures.
What is transpiration?
The volume of water that is evaporated by the plant is many times higher than the amount contained in the culture. In modern agricultural practice, the issue of economical use of moisture is one of the most relevant. According to K. A. Timiryazev, the transpiration process in its usual volume is a physiological evil. In fact, it is not considered necessary for the plant. For example, if you grow crops in conditions of low and high humidity, in the first case, transpiration (evaporation) will be more intense. In this case, the growth of plants will be the same or even better in the second case.
Transpiration: value
To a certain extent, it is useful to the plant. Explaining what transpiration is, it is first necessary to note its protective function. Evaporation helps protect the plant from overheating under direct sunlight. For example, the difference in temperature of leaves that give and do not give moisture can fluctuate within 7 degrees. This is of particular importance for the photosynthesis process. The fact is that with overheating, the destruction of chloroplasts begins. This, in turn, significantly slows down photosynthesis. The optimum temperature for it is in the range of 30-33 degrees. So what is transpiration? This is a plant protection product that allows them to tolerate high temperatures well.
Water continuity
Explaining what transpiration is, one should pay attention to one more positive property of it. It promotes the continuous movement of water from the root system to the leaves. This binds all the elements of the plant into one. Together with moisture, mineral compounds and part of organic substances move along the organs of culture. The more intense the transpiration process, the faster their movement. Some compounds may pass into cells in a passive manner. Briefly speaking, transpiration is an accelerator of substance delivery.
Classification
Having understood what transpiration is, we can proceed to consider its types. In science, there are two types of it. Transpiration can be stomatal and cuticular. In the first case, evaporation is carried out through the stomata, in the second - from the entire surface of the sheet. This distinction was first adopted in 1877. To make sure that transpiration is not only through the stomata, can be quite simple. For example, you can take the leaves of an apple tree. They have stomata only from the bottom. This surface should be smeared with petroleum jelly. Evaporation will continue through the cuticles, but to a lesser extent.
Stomatal Evaporation Structure
Transpiration includes:
- The movement of water from xylem vessels along the cell walls and symplast.
- Evaporation into the submuscular cavities and intercellular spaces with further diffusion into the surrounding air through stomatal fissures.
The lower the relative humidity, the lower the water potential of the surrounding atmosphere. If it is smaller than in the submandibular cavities, evaporation will occur outward. Regulation of transpiration can be stomatal and extra stomatal. The first is carried out by opening and closing the pores. With full cover, transpiration is reduced by approximately 90%.
Intensity
The frequency of daily transpiration is observed in many plants. However, the functioning of stomata varies in different types of crops. In shade-tolerant plants, trees, many types of cereals and other hydrostable plantings, which are characterized by perfect regulation of stomatal transpiration, it begins at dawn. Evaporation reaches its maximum in the morning. By noon, the transpiration rate decreases. Its increase is again observed in the evening with a decrease in air temperature. This evaporation rate causes minor daily changes in the osmotic pressure and volume of water in the leaves. In hydrolabile (having the ability to tolerate sharp fluctuations in the moisture content during the day), one-peak evaporation occurs with a maximum at noon. And in that, and in another case, transpiration at night will be minimal or completely absent.