About How Much Water Is Transpired by Plants

Plants need water to grow and function.

Transpiration is the evaporation of water from plant leaves through the stomata, which are small pores or openings on the leaf. Evapotranspiration (ET) is a combination of evaporation and transpiration. Evaporation includes water entering the atmosphere from ground water and bodies of water.

Why do plants transpire?

Some plants conserve water better than others.

Plants transpire to cool themselves in hot weather, to move nutrients upward, and to keep the plant hydrated, though moving nutrients isn't as important as cooling. More water is lost when it's hot, and grass transpires more in the light than in the dark. All these affect how much water is transpired.

When and how do plants transpire?

Plant leaves have stomata to regulate transpiration.

Transpiration rates vary depending on temperature, humidity, wind, light, type of plant and how old it is. As the temperature rises, water evaporates faster; it also evaporates faster if the air is dry. When a plant loses too much water, the stomata close and transpiration slows down.

How much water can be transpired?

Houseplants need to be watered carefully.

A leaf can transpire much more than its body weight. A houseplant may transpire its body weight each day. Plants transpire over 99 per cent of their water intake in a lifetime, according to Kansas State University' s Weather Data Library. The U.S. Geological Survey reports that a big oak tree can transpire 40,000 gallons of water a year and an acre of corn up to 4,000 gallons a day.

References

• US Geological Survey: The Water Cycle: Evapotranspiration
• NOAA: Northwest River Forecast Center: Hydrologic Cycle
• Kansas State University Research & Extension: Weather Data Library: What is ET?
• Michigan State University Science Theatre: Why do my plants need so much water?
• Idaho State Climate Services: Introduction: City of Moscow Water Conservation Ordinance: City of Moscow Water Conservation Ordinance: Evapotranspiration Basics

Resources

• University of Florida: IFAS Extension: Evaporation and Evapotranspiration
• Plant and Soil Sciences eLibrary: Transpiration