Transpiration

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Transpiration may also refer to sweating and hyperhydrosis.

Transpiration is a process caused by the evaporation of water from leaves of plants and its corresponding uptake from roots in the soil. Transpiration cools plants down and enables mass flow of minerals to where it is needed in the plant. 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. Water is absorbed at the roots by osmosis, and any dissolved solutes travel with it through the xylem.

The rate of transpiration is directly related to whether the stomata are open or closed. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, wind speed, and water supply. Transpiration rate is measured by a potometer. There are two kinds: mass potometers, which measure transpiration, and bubble potometers, which measure water uptake. 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 inside the leaf and the outside air causing water to leave the leaf more quickly, therefore 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. About 90% of the water that enters a plant's roots is used for this process. 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., [c]rop plants transpire 200 to 1000 kg of water for every kg of dry matter produced) .

Desert plants and conifers have specially adapted structures, such as needles or thick, fleshy leaves to reduce transpiration and its effects.

See also

• Antitranspirant
• Ecohydrology
• Evapotranspiration
• Moisture stress
• Measuring transpiration with a potometer
• Transpirational pull

References

• [A description of transpiration, including a short animation illustrating the process]

 

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