Tree Transpiration – how does it work?


Tree transpiration is the process by which moisture (water) is carried through the tree from the roots to small pores on the underside of leaves. There it changes into vapor and is released into the atmosphere. About 10 percent of the moisture in the atmosphere is released by trees and plants through this process of transpiration. The remaining 90 percent is mainly supplied by evaporation by oceans, seas, rivers and other bodies of water.

But how does tree transpiration work exactly?

Surprisingly, tree transpiration takes up about 98% of the tree’s energym which is a vital function that the tree performs. Water moves from the soil into the tree’s roots up through the trunk and into the leaves. The water, which is warmed by the sun, turns into vapor. Yes, it evaporates. It then passes out through thousands of tiny spores (stomata) which reside mostly on the underside of the leaf surface.

What are the two main functions of tree transpiration?

The two main functions of tree transpiration are cooling the tree and pumping water and minerals to the leaves for photosynthesis to occur.

How do trees, through transpiration, prevent dehydration?

Since tree transpiration is an evaporative cooling system that brings down the temperature of the tree, it must be regulated. Why? It can lead to water loss. Within the tree, there are guard cells on the stomata. When water moves into the guard cells, they swell and arch open. As water moves out, the guard cells relax and close. The guard cells are sensitive to light intensity, temperature, wind, relative humidity and carbon dioxide concentrations inside the leaf. The stomata must also open to take in carbon dioxide for photosynthesis, especially during the morning on sunny days. The more they are open, the more the tree will transpire and lose water. If you water your trees early in the morning, this will support plant energy especially during the summer.

How do trees pump water and minerals to leaves so photosynthesis can occur?

Trees pump water and minerals via transpiration similar to the way you suck liquid through a straw. Water and minerals move against the force of gravity and go up. The tiny capillaries called xylem are water channels via which water travels. Since water has an extremely strong bonding process, the sucking force created when water gets to the top of the channel causes its evaporation. However, the fact that the tree can create this force is due to negative pressure which lifts the column of water to the leaf surface.


Credit: Austin Tree Source