How Much Water Does a Tree Raise from Its Roots to Its Leaves in a Day?

Photosynthesis and Transpiration

• The leaf provides all the food for the tree through photosynthesis. Sunlight provides the energy for photosynthesis, and for maximum photosynthesis, the leaf spreads a maximum surface to the sunlight. Carbon dioxide is also necessary, but the plant membrane is impervious to the gaseous form of carbon dioxide, so it's only available to the plant cells through contact with water. The tree's water needs are part of the cost of photosynthesis.

Water Uptake

• Water and nutrients are absorbed through the tree's roots, and the resulting sap is transported to the crown of a tree through the xylem. The xylem sap rises against gravity, pulled through a process that starts with water evaporating from the leaves. Water has a tendency to leave one place in favor of another place with less water; this tendency is measured as water potential. Water is pulled from the xylem to replace the transpired water.

How Trees Regulate Water Loss

• The stomatal opening is a minute opening that takes up about 1 percent of the leaf surface; more than 90 percent of the water transpired from leaves is lost through the stomata. Stomata can open and close to regulate water loss. Stomatal movement responds to temperature, carbon dioxide concentration, and light. Most trees have adapted to tolerate drought through rapid stomatal opening and closing, developing deep, wide root systems, the ability to store water in its organs, and other strategies.

Trees in the Water Cycle

• The water that trees transpire is not truly lost. Trees are part of the cycle that circulates water from the soil to the clouds and back. Transpiration, together with evaporation of moisture on land, provides almost two-thirds of the moisture that falls as precipitation on land surfaces. Forests capture and store water, and are an important part of the clean drinking water needed by the billions of people and other living creatures in the world.