Why do plants lose water so easily?

Plants are vital to life on earth, providing us with the oxygen we breathe and being the foundation of the food chain. However, when you look closer at individual plants, you will notice how they lose water easily. But why is that so?

Plant anatomy: Stomata and Transpiration

Plants have microscopic pores on their surface called stomata. These pores are fundamental to plant survival, as they allow carbon dioxide to enter and oxygen to exit during photosynthesis. However, an inevitable consequence of this opening is water loss through a process called transpiration. As the plant takes in carbon dioxide, it loses water vapor through the stomata. This process is essential for the plant to maintain a healthy internal temperature and maintain proper chemical balance, but it comes at the cost of water loss.

Factors Affecting Transpiration Rate

Transpiration rates vary depending on various internal and external factors, including:

Temperature: Higher temperatures cause faster transpiration rates, as heat energy causes water molecules inside the plant to evaporate more easily

Humidity: When the humidity level is low, there is a low concentration of water vapor in the air, which causes water to leave the plant through transpiration faster. Conversely, high humidity will cause the opposite effect.

Light Intensity: The more light a plant receives, the higher its photosynthetic rates and the higher its transpiration rates.

Wind: Windy conditions increase the movement of air, which moves away the layer of water vapor that forms around the plant. This movement creates a lower concentration of water vapor in the air, leading to a higher transpiration rate.

Adaptations to Reduce Water Loss

Plants have evolved several adaptations to limit their water loss without compromising their survival, including:

Small Leaf Size: Plants in hot and dry habitats, such as cacti, have evolved to have small leaves or no leaves whatsoever, reducing their surface areas for transpiration

Thick Cuticles: Plants growing in arid habitats have thick cuticles on their leaves, which are waxy layers that limit the diffusion of water vapor out of the plant

CAM Photosynthesis: Some plants, like succulents, perform Crassulacean acid metabolism (CAM) photosynthesis, which allows them to open their stomata at night when temperatures are lower and humidity levels are higher, then store carbon dioxide for use during the day.

Transpiration Stream: The transpiration stream is the movement of water through the plant from the roots, which are in contact with soil and groundwater, up to the leaves. Plants can regulate the degree of opening of their stomata and the pressure within their cells to reduce water loss in dry conditions.

Conclusion

Plants lose water easily through transpiration, but this process is essential to their survival. Transpiration rates are influenced by various internal and external factors, from light and temperature to wind and humidity. Plants have several adaptations that allow them to limit their water loss without endangering their survival.