transpiration

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transpiration

 [trans″pĭ-ra´shun]
discharge of air, vapor, or sweat through the skin.

tran·spi·ra·tion

(tran'spī-rā'shŭn),
Passage of watery vapor through the skin or any membrane.
See also: insensible perspiration.
[trans- + L. spiro, pp. -atus, to breathe]

transpiration

(trăn′spə-rā′shən)
n.
The act or process of transpiring, especially through the stomata of plant tissue or the pores of the skin.

tran′spi·ra′tion·al adj.

tran·spi·ra·tion

(trans'pir-ā'shŭn)
Passage of water vapor through the skin or any membrane.
See also: insensible perspiration
[trans- + L. spiro, pp. -atus, to breathe]

transpiration

the loss of water vapour from the inside of a leaf to the outside atmosphere, via STOMATA and LENTICELS. Transpiration exerts a considerable upward pressure in the stem and is thought to be part of the explanation of how water ascends from roots to leaves.

The rate at which transpiration proceeds depends upon several physical factors:

  1. (a) the Water Vapour Pressure at the MESOPHYLL cell surface inside the leaf. The evaporating surface is saturated and will have a VAPOUR PRESSURE (WVPsatn) that is highly affected by ambient temperature. For example, at 20 °C the WVPsatn = 2.34 kPa, at 10 °C the WVPsatn = 1.23 kPa.
  2. (b) the Water Vapour Pressure in the outside air (WVPa ir ), the maximum value being equal to WVPsatn at that temperature. If there is the same temperature inside and outside the leaf, the rate of flow of water vapour between the surface of the mesophyll cell and the outside is the difference between WVPsatn and WVPair; i.e:WVPdiff= WVPsatn - WVPair Thus the greater the WVPdi ff value, the greater the diffusion gradient and the higher the transpiration rate.
  3. (c) the size and number of stomatal pores per unit area of a leaf. The smaller the pore diameter, the greater the resistance to water vapour diffusion. The presence of'vapour shells’ over each stoma creates a boundary layer of high Water Vapour Pressure in still air, which will slow down the transpiration rate since it increases the WVPa ir value. This effect is most important when the pore diameter is large. In moving air, the vapour shells cannot form and thus transpiration rates increase.
  4. (d) the stomatal and leaf structure, which are modified in some XEROPHYTES to reduce transpiration rates.
  5. (e) a constant supply of water from the roots.
References in periodicals archive ?
The eighteen experiments included black and white and color photography, live mice, radiation phenomena, reentry physics including transpirational cooling, electromagnetic propagation and fuel cell prototypes.
We found that the transpirational cooling by vegetation can reduce air temperatures inside an urban street canyon and in particular at the pedestrian level (2 m above ground).
For example, stomatal closure is one of the first adaptive responses plants display to increasing water stress, in an attempt to reduce leaf transpirational losses and prevent development of lethal water deficits in their tissues (Kramer and Boyer, 1995).
However, at this time Cryptantha derived only a small fraction of its transpirational water from the water pulse.
Li's analyses of these gems of short fiction illustrate well the veracity of Li's claim that, "while Louie's transpirational narrative strategy and Hwang's transvestic theater are capable of bringing Asian American characters to the threshold of visibility, these figures of artistic performance reveal far more about the threat of Asian American derealization in the representational democracy of the United States" (p.
Transpirational pull is the main process controlling the movement of water and nutrients from the roots to the leaves.
Transpirational demands from cover crops coincided with high precipitation events, explaining why %VSWC in cover-crop treatments were never lower than the control.
The transpirational pull of water from the root system up through the tree is therefore regulated.
Lowered absorption of the inorganic nutrients can result from interference in nutrient uptake and the unloading mechanism and reduced transpirational flow.
On the other hand, potassium and, to a lesser extent, phosphorus, are not present in soil solution in sufficient quantities for mass flow of the transpirational stream to provide enough nutrients at the root surface for uptake.
Flowers, "Silicon reduces sodium uptake in rice (Oryza sativa L.) in saline conditions and this is accounted for by a reduction in the transpirational bypass flow," Plant, Cell and Environment, vol.