Relative humidity:В As the relative humidity of the air surrounding the plant rises the transpiration rate falls.Higher temperatures cause the plant cells which control the openings (stoma) where water is released to the atmosphere to open, whereas colder temperatures cause the openings to close. Temperature: Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses.There are a number of factors that determine transpiration rates: The amount of water that plants transpire varies greatly geographically and over time. An acre of corn gives off about 3,000-4,000 gallons (11,400-15,100 liters) of water each day, and a large oak tree can transpire 40,000 gallons (151,000 liters) per year.ДЄtmospheric factors affecting transpiration During a growing season, a leaf will transpire many times more water than its own weight. As this picture shows, transpired water will condense on the inside of the bag. One way to visualize transpiration is to put a plastic bag around some plant leaves. Just because you can't see the water doesn't mean it is not being put into the air, though. Since the water is evaporating from the leaf surfaces, you don't just go out and see the leaves 'breathing'. Plant transpiration is pretty much an invisible process. During dry periods, transpiration can contribute to the loss of moisture in the upper soil zone, which can have an effect on vegetation and food-crop fields.ДЄfter a plastic bag is wrapped around part of a plant, the inside of the bag becomes misty with transpired water vapor. Transpiration rates vary widely depending on weather conditions, such as temperature, humidity, sunlight availability and intensity, precipitation, soil type and saturation, wind, and land slope. Some of this water is returned to the air by transpiration. Plants put down roots into the soil to draw water and nutrients up into the stems and leaves. If the bag had been wrapped around the soil below it, too, then even more water vapor would have been released, as water also evaporates from the soil. Just as you release water vapor when you breathe, plants do, too вЂ“ although the term 'transpire' is more appropriate than 'breathe.' This picture shows water vapor transpired from plant leaves after a plastic bag has been tied around the stem for about an hour. Transpiration: The release of water from plant leaves Studies have revealed that transpiration accounts for about 10 percent of the moisture in the atmosphere, with oceans, seas, and other bodies of water ( lakes, rivers, streams) providing nearly 90 percent, and a tiny amount coming from sublimation (ice changing into water vapor without first becoming liquid). The transpiration aspect of evapotranspiration is essentially evaporation of water from plant leaves. The banner at the top of this page offers an even more simple definition. Here, evapotranspiration is defined as the water lost to the atmosphere from the ground surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants whose roots tap the capillary fringe of the groundwater table. But, since we have a Web page just about evaporation, our definition of evapotranspiration will not include evaporation from surface water. Some definitions include evaporation from surface-water bodies, even the oceans. In general, evapotranspiration is the sum of evaporation and transpiration. If you search for the definition of evapotranspiration, you will find that it varies. Scientists refer to the combination of evaporation and transpiration as evapotranspiration, abbreviated ET. Any dew or droplets of water present on stems and leaves of the plant eventually evaporates as well. Water also evaporates directly into the atmosphere from soil in the vicinity of the plant. Overall, this uptake of water at the roots, transport of water through plant tissues, and release of vapor by leaves is known as transpiration. The water eventually is released to the atmosphere as vapor via the plant's stomata - tiny, closeable, pore-like structures on the surfaces of leaves. That water is then used for metabolic and physiologic functions. The typical plant, including any found in a landscape, absorbs water from the soil through its roots.

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