transpiration

The loss of water vapour from a plant. It mainly occurs from leaves via the stomata, which partially control the process by opening and closing in response to humidity changes in the air. The process cools and prevents damage to the leaves in hot weather, and helps draw water up from the roots to other parts of the plant.

Transpiration is the evaporation of water from aerial parts of plants, especially leaves but also stems, flowers and fruits. Mass flow is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, wind speed, and soil water supply. The reason that an increase in temperature will cause an increase in transpiration rate is because an increase in temperature will cause more water to evaporate from the cell walls inside the leaf. This will increase the water potential gradient between the leaf interior and the outside air causing water to leave the leaf more quickly, thereby increasing the rate of transpiration.

A fully grown tree may lose several hundred gallons (a few cubic meters) of water through its leaves on a hot, dry day. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced) (Martin, Leonard & There are two kinds: mass potometers, which measure transpiration, and bubble potometers, which measure water uptake.

Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water.