स्वतन्त्र विश्वकोश, नेपाली विकिपिडियाबाट
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Stoma in a tomato leaf shown via colorised scanning electron microscope.
The clouds in this image of the Amazon Rainforest are a result of transpiration.
Some xerophytes will reduce the surface of their leaves during water deficiencies (left). If temperatures are cool enough and water levels are adequate the leaves expand again (right).

बोटबिरुवाले आफुमा भएको पानीलाई निश्काशन गर्ने प्रक्रियालाई उत्स्वेदनयसका बारेमा ध्वनी  प्रक्रिया भनिन्छ । यसलाई अङ्ग्रेजीमा ट्रान्स्पिरेसन (Transpiration)भनिन्छ । यो प्रक्रिया झन्डै वास्पिकरण प्रक्रिया जस्तै हुन्छ । It is a part of the water cycle, and it is the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants they are more numerous on the undersides of the foliage. The stoma are bordered by guard cells that open and close the pore.[१] Leaf transpiration occurs through stomata, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots.

Mass flow of liquid water from the roots to the leaves 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 mineral nutrients travel with it through the xylem.

The rate of transpiration is directly related to the evaporation of water particles from plant surfaces, especially from the surface openings, or stomates, on leaves. Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the surfaces of the epidermal cells of the leaves. The amount of water given off depends somewhat upon how much water the roots of the plant have absorbed. It also depends upon such environmental conditions as sunlight, humidity, winds and temperature. A plant should not be transplanted in full sunshine because it may lose too much water and wilt before the damaged roots can supply enough water. Transpiration occurs as the sun warms the water inside the blade. The warming changes much of the water into water vapour. This gas can then escape through the stomata. Transpiration helps cool the inside of the leaf because the escaping vapor has absorbed heat. Transpiration helps cool the inside of the leaf because the escaping vapor has absorbed heat. degree of stomatal opening, and to the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with surrounding light intensity,[२] temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.

A fully grown tree may lose several hundred gallons of water through its leaves on a hot, dry day. About ९०% 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 २०० and १००० (i.e., crop plants transpire २०० to १००० kg of water for every kg of dry matter produced).[३]

Transpiration rate of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, photosynthesis systems and heat balance sap flow gauges.

Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low. Many desert plants have a special type of photosynthesis, termed crassulacean acid metabolism or CAM photosynthesis in which the stomata are closed during the day and open at night when transpiration will be lower.

See also[सम्पादन गर्ने]

References[सम्पादन गर्ने]

  1. Benjamin Cummins (२००७), Biological Science (3 संस्करण), Freeman, Scott, पृ: २१५। 
  2. Debbie Swarthout and C.Michael Hogan. 2010. Stomata. Encyclopedia of Earth. National Council for Science and the Environment, Washington DC
  3. Martin, J.; Leonard, W.; Stamp, D. (१९७६), Principles of Field Crop Production (Third Edition), New York: Macmillan Publishing Co., Inc., ISBN 0-02-376720-0 

External links[सम्पादन गर्ने]