Plants need water in just the right amount. Soil holds water when it has organic matter content such as compost. Sandy soil causes water to flow away from plants; heavy claylike soil retains water excessively and plant roots rot. Water content is easily checked by putting your finger in the soil to your knuckle. If you feel moisture, the plant has adequate water.
Water and Nutrients
Vegetable plants need 13 minerals from soil to provide healthy nutrient content. Water carries the 13 minerals from the surrounding soil to the plant's root system. Water and minerals are absorbed by roots and carried into the plant stems, leaves and fruit or vegetable. Water moves continuously from soil to roots to plant leaves.
"Most of the water absorption is carried out by the younger parts of the roots," according to Anne Bruce, of online science magazine Microscopy, in her article "Water Movement Through a Plant." Root hairs are projections of epidermal tissue just below the growing tip of the root. Water is taken into root hairs through osmosis and travels to all portions of the plant.
Chemical Processes in Water
Chemical and biochemical processes that support plant metabolism take place in water. Water acts as a solvent for dissolved sugars and minerals transported throughout the plant. Water evaporation in the spaces between cells acts as a cooling mechanism that allows plants to maintain favorable temperatures necessary for metabolic processes.
Water is released from small openings in the leaf called stomata. Stomata are found on one or both leaf sides, depending on the species. It is carried into the atmosphere as water vapor in a process called transpiration. Total water loss from soil and wet plant surfaces is known as evapotranspiration.
Effects of Underwatering
When roots do not receive adequate water, the plant partially or completely shuts its stomata to preserve the water it has. Photosynthesis is decreased because open stomata are necessary for carbon dioxide absorption. Photosynthesis is the process plants use to create food from sunlight. Decreased photosynthesis results in underdeveloped plants and decreased production of vegetables or flowers.