Advantages of Transpiration :
(a) Ascent of sap : Ascent of sap mostly occurs due to pull exerted by transpiration of water.
(b) Removal of excess water : It has been held that plants absorb far more amount of water than is actually required by them. Transpiration, therefore, removes the excess of water.
(c) Cooling effect : Radiant heat falling on the plants increases their temperature which may be dangerous to the plants. Transpiration, by evaporating water, lowers down their temperature.
(d) Mechanical tissue: The development of mechanical tissues which is essential for providing rigidity and strength to the plants, is favoured by the increase in transpiration.
(e) Distribution of Mineral Salts : Mineral salts are mostly distributed by rising column of sap.
(f) Increasing Concentration of Mineral Salts : The sap absorbed from the soil contains low concentration of mineral salts. The loss of water through transpiration increases the concentration of mineral salts in the plant.
(g) Root System : Transpiration help in better development of root system which is required for support and absorption of mineral salts.
(h) Quality of Fruits : The ash and sugar content of the fruit increases with the increase in transpiration.
(i) Resistance : Excessive transpiration induces
hardening and resistance to moderate drought. Disadvantages of Transpiration:
(a) Wilting: Wilting or loss of turgidity is quite common during noon due to transpiration being higher than the rate of water absorption. Wilting reduces photosynthesis and other metabolic activities.
(b) Reduced Growth : Transpiration reduces
availability of water inside the plant. Water deficit decrease the growth and hence the plant gives a stunted appearance
(c) Reduced Yield : As reported by Tumarov (1925), a single wilting reduces by 50%. It is because decreased availability of water inside the plant checks meristematic activity and hence the formation of flowers, fruits and seeds.
(d) Abscissic Acid : Water stress produces abscissic acid. Abscissic acid prevents several plant processes and promotes abscission of leaves, flowers and fruits.
(e) Wastage of Energy : Since 98-99% of absorbed water is lost through transpiration, the energy used in absorption and conduction of water goes waste.
(f) Modification : In order to reduce transpiration :
during critical periods, the plants produce several types of modification like thick cuticle, hair, prickles, spines, thorns, sunken stomata, phylloclades, cladodes, etc.