Transpiration in plants

Many people don’t know, but plants also lose water through transpiration. In fact, they lose much more water than animals, so they consume much more of this product. It is estimated that vegetables lose 99% of the water absorbed to the environment in the form of steam, that is, through transpiration.

→ Where does sweating occur?

Transpiration occurs anywhere on the plant that is above the ground, however, most transpiration occurs in the leaves. The greatest loss of water occurs through the stomata , small openings surrounded by guard cells located in the epidermis. A small part of water is also lost through the cuticle and lenticels.

Stomatal transpiration occurs in two stages:

1. Evaporation of water that is present on the surface of the cell wall of the cells that surround the intercellular spaces of the leaves;

2. Water vapor diffuses into the atmosphere through the stomata.

It can be seen, therefore, that stomatal opening and closing are directly related to the transpiration process. When the stomata closes, there is a decrease in the loss of water through the leaves, however, when it closes, the stomata prevents the entry of carbon dioxide, which is essential for photosynthesis. To resolve this issue, some plants perform their gas exchange at night.

→ Is transpiration a bad process for the plant?

Transpiration, if it occurs in excess, can be extremely harmful, as the exaggerated loss of water can lead the plant to dehydration. Even so, this process is necessary. As said, transpiration is directly related to the capture of carbon dioxide. Failure to uptake affects the photosynthetic rate. It is worth noting, however, that carbon dioxide is also produced by the plant in the respiration process, which ensures that photosynthesis takes place at low levels, when the stomata are closed.

Transpiration is also important to ensure the circulation of raw sap in the plant’s body, a theory called tension-cohesion. According to this theory, water from the xylem is practically pulled to replace the water lost in transpiration.

→ Factors that influence the rate of transpiration

Some factors affect the rate of transpiration, in addition to the aforementioned opening and closing of stomata. Look:

• Temperature : Increasing temperature increases the rate of transpiration;
• Humidity: Humidity causes a decrease in the rate of transpiration;
• Air currents: Dry wind increases the rate of transpiration.

We cannot forget also factors of the plant itself, such as evaporation surface, cuticle thickness and presence of trichomes . The latter lower the leaf temperature, reducing water loss.