Introductory Crop Physiology (1+1)

Significance of Transpiration

Significance of Transpiration

• Plants waste much of their energy in absorbing large quantities of water and most of which is ultimately lost through transpiration.
• Transpiration is a unique feature in the plant system and referred as necessary evil as it is advantageous to plant under certain circumstances and harmful in some other situations.
I. Transpiration is necessary
1. Role in the movement of water

• Water plays an important role in the upward movement of water i.e. Ascent of sap in plants.
• But, it does not mean that the translocation of water will be stopped without it.
2. Role in the absorption and translocation of mineral salts

• Absorption of water and mineral salts are entirely independent process.
• Therefore transpiration has nothing to do with the absorption of mineral salts.
• However, once mineral salts have been absorbed by the plants, their further translocation and distribution may be facilitated by transpiration through translocation of water in the xylem elements.
3. Role of regulation of temperature

• Some of the light energy absorbed by the leaves is utilized in photosynthesis, rest is converted into heat energy which raise the leaf temperature.
• Transpiration plays an important role in controlling the temperature of the plants.
• Rapid evaporation of water from the aerial parts of the plant through transpiration brings down the temperature and thus prevents them from excessive heating.
• Transpiration is one of the chief ways for the dissipation of excess energy, which the plant receives from the sun.
• Shull (1930) estimated that approximately 0.8 cal of energy is received upon each square cm of leaf surface per minute, of which about 10% is reflected and 25% is transmitted.
• The remaining 65% (0.52 cal) will increase the temperature of the leaves very rapidly.
• If the weight of the leaf tissue is 0.02g/cm2 with the specific heat of 0.879, then the rise in temperature would be at 32ºC per minute.
• With this rate of increase in temperature, the plants will be killed in less than two minutes, if there is no dissipation of energy.
• Transpiration plays a significant role here.
• It helps in dissipating this excess energy which will otherwise raise the temperature.
4. Role on growth and development:

• Winneberger (1958) has observed that the buds of hardy pear cease to grow under conditions of high humidity and that under the same conditions growth of the sunflower plant is reduced to about half of the normal.
• So it is clear that transpiration is necessary factor in the normal growth of these two plants.
• Most important point is that cell growth depends on absorption of water which is passively absorbed by the roots of plants due to transpiration pull.
• Plants showing high rate of transpiration exhibit adequate development of mechanical tissues. Transpiration also shows that plants showing high rate of transpiration exhibit extensive root system.
5. Involves in improvement in the quality of fruits:

• Increased sugar and mineral contents of fruits follows high rate of transpiration.
6. Transpiration help in hardening process:

• Transpiration induces hardening which imparts resistance of plant to drought.
7. Transpiration help in removal of excess water:

• It has been held that plants absorb far more amount of water than is actually used by the plant by the plant. Transpiration removes excess of water.


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