The Importance of Water to Plants

Water is essential to plant life. To survive, plants need water, as well as nutrients, which are absorbed by the roots from the soil. Plants are 90 percent water. Water is transported throughout the plant almost continuously to keep its vital processes working.

Root System

Roots absorb water from the soil, which is then carried through the plant. Much of the water is taken up through the root hairs, which are tiny rootlets that penetrate the soil around the roots and increase the root's surface area. Water is a solvent that moves minerals from the soil up through the plant. As the soil dries, the root growth slows. If the soil is saturated with water, the roots could drown.

Photosynthesis

Water is used for the chemical and biochemical processes supporting plant metabolism. The plant uses sunlight to split water into hydrogen and oxygen. The hydrogen then uses carbon dioxide in the air to make sugar. The oxygen is discarded into the atmosphere as water vapor. Plants use oxygen to burn sugar and make energy for life processes. The sole purpose of leaves is to collect light and make sugar. Leaves get water from the roots, and air enters the leaves through small holes called stomates. Open stomates let in air but also cause the plant to lose water through evaporation. If these holes close to conserve water, photosynthesis and sugar production are halted.

Growth

Cell division and cell expansion are the two ways plants grow. Cells grow by taking in water. Cell division creates additional cells, while cell expansion is an increase in the size of the cell. If water is limited during periods of growth, the final cell size is diminished, which leads to fewer and smaller leaves, smaller fruit, shorter, thicker stems and a smaller root system. The lack of water results in smaller, weaker plants. For fruiting plants, a critical time is after bloom, when the fruit begins to grow. Fruit, shoots and new leaves require plenty of water and almost all the sugar the leaves produce. Lack of water minimizes the growth of new shoots and leaves, which means less sugar is available for fruit growth. The growth of the root system slows down, so it might be necessary to use irrigation to keep the roots moist.

Wilting

Well-watered plants keep their shape because of the internal pressure of water in the cells, called turgor pressure. When there is insufficient water, the pressure drops and causes the plant to wilt. This pressure is also essential for plant cell expansion, which leads to plant growth.

Water Stress

Water regulates the opening and closing of stomata, which in turn regulates transpiration and photosynthesis. If too little water is available to the root system, the plant will reduce the amount of water lost through transpiration. This causes reduced photosynthesis because the necessary carbon dioxide enters the plant through the stomata. Decreases in photosynthesis result in decreased crop yields.

References

• Soil Plant Water Relationships
• Water and Plant Growth
• Plant Growth Factors: Water