Some definitions include evaporation from surface-water bodies , even the oceans. But, since we have a Web page just about evaporation, our definition of evapotranspiration will not include evaporation from surface water. 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.
The banner at the top of this page offers an even more simple definition. The transpiration aspect of evapotranspiration is essentially evaporation 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.
Just as you release water vapor when you breathe, plants do, too — although the term "transpire" is more appropriate than "breathe. 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. Plants put down roots into the soil to draw water and nutrients up into the stems and leaves. Some of this water is returned to the air by transpiration. 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.
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.
After a plastic bag is wrapped around part of a plant, the inside of the bag becomes misty with transpired water vapor. Plant transpiration is pretty much an invisible process. Since the water is evaporating from the leaf surfaces, you don't just go out and see the leaves "breathing". Just because you can't see the water doesn't mean it is not being put into the air, though. One way to visualize transpiration is to put a plastic bag around some plant leaves.
As this picture shows, transpired water will condense on the inside of the bag. During a growing season, a leaf will transpire many times more water than its own weight. An acre of corn gives off about 3,, gallons 11,, liters of water each day, and a large oak tree can transpire 40, gallons , liters per year.
The amount of water that plants transpire varies greatly geographically and over time. There are a number of factors that determine transpiration rates:. In many places, the top layer of the soil where plant roots are located is above the water table and thus is often wet to some extent, but is not totally saturated, as is soil below the water table. The soil above the water table gets wet when it rains as water infiltrates into it from the surface, But, it will dry out without additional precipitation.
Since the water table is usually below the depth of the plant roots, the plants are dependent on water supplied by precipitation.
This second process is called infiltration — water moves through pore spaces between soil particles or rocks. Once the water is in the hydrosphere or geosphere, it can be used by living things. Plants can take water from the soils, and animals can drink water from rivers and lakes or eat plants. Even microbes deep in the ground live in tiny films of water surrounding rocks. The water will then stay in the biosphere until released through evaporation, transpiration, excretion, decay, respiration and combustion and the whole process begins again.
It may stay in the hydrosphere or geosphere for a long time such as in aquifers or it may very quickly return to the atmosphere. Water cycle models use simple materials to observe the interactions along the water cycle.
Check them out. An answer to this question is provided by one of our experts who specializes in biology. Let us know how much you liked it and give it a rating. Cite this page Select a citation style:. References Academic. Reference Academic. Bibliography Academic. Work Cited "What role does cellular respiration play in the water cycle? Lipid peroxidation is a natural metabolic process under normal aerobic conditions and is one of the most investigated ROS actions on membrane structure and function Blokhina et al.
It is widely reported that ROS induce peroxidation of membrane lipids leading to membrane damages, often associated with increased permeability and loss of integrity Kumar and Knowles, ; Bolu and Polle, Nonetheless, the plants of cv.
CS preserved the ability of their cell membranes to control the rate of ion movement in and out of cells, since no electrolyte leakage was observed in leaves of stressed-plants. Survival under drought conditions is closely associated with the plant ability in delaying or preventing the oxidation of cellular components and metabolites Singh and Rajini, Under several adverse environmental conditions the AOX is up-regulated Rizhsky et al.
Actually, it is very likely that a special modulation of the alternative pathway may account, at least in part, for the drought tolerance of Vitis vinifera as the AOX seems to be constitutively activated in this species These values are much higher than that found to wheat Bartoli et al.
In conclusion, the present results confirm and expand the notion that Vitis vinifera L. Cabernet Sauvignon is able to adapt their photosynthetic process to a reduction in water availability Iaccono and Sommer, ; Guan et al. The results also reveal that the AOX activation integrates an intrinsic mechanism of this species, which maintains its cellular integrity and functionality under drought stress. Further studies should be directed to understanding the mechanistic details of this AOX control towards developing new biotechnological strategies to improve the stress tolerance, productivity and fruit quality of this important plant species.
The author's would like to thank Vitaceae Brasil for providing the grapevine plants. Abrir menu Brasil. Brazilian Journal of Plant Physiology. Abrir menu. Plant Physiol. Martim Mirella P. Santos Anderson L. Viana Arnoldo R.
Asada, K. Plant Physiology, Journal of Experimental Botany, Annals of Botany, Blum, A Improving wheat grain filling under stress by stem reserve mobilization. Euphytica, Blum, A Crop response to drought and the interpretation of adaptation. Journal Plant Growth regulation, In: Dey, P. M and Harborne, J. B eds , Plant Biochemistry, pp. Chaves, MM Effects of water deficits on carbon assimilation.
Functional Plant biology, Plant Physiology and Biochemistry, Plant Prod. Science,
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