12. M.Sc -Transpiration.ppt
- 1. TRANSPIRATION • The loss of water from aerial parts of plants in the form of vapor is known as transpiration. • The loose arrangement of the living thin walled mesophyll cells, which results in an abundance of inter cellular space provides an ideal condition for the vaporation of water from internal leaf surface. • Part of the epidermal surface of the leaf is made up of a great number of microscopic pores called stomata.
- 3. •Water vapor collected in the intercellular spaces of leaf mesophyll diffuse into the atmosphere through the open stomata. This form of transpiration is termed as stomatal transpiration. In addition to stomatal transpiration, water is lost as vapor directly from leaf Surfaces and through lenticels (small opening in the corky tissue covering stems and twigs). The former is called cuticular transpiration and the later lenticular transpiration.
- 5. 1) Stomatal Transpiration: • The stomatal transpiration accounts to 80 to 98% of the total transpiration loss from plants (tree to herbaceous plants). Under very dry conditions, stomata are closed and water loss occurs through the cuticle and lenticels. 2) Cuticular Transpiration: • The cuticular transpiration accounts to 2 to 20% of the total transpiration loss from plant (xerophytes to mesophytes). The cuticle although retards water loss, is some what permeable to water vapor. In plants with thick cuticles, this form of transpiration is insignificant
- 6. 3) Lenticular Transpiration • The lenticular transpiration amount to 0.1 to 1% of the total transpiration loss from plants which is insignificant when compared to stomatal transpiration. • However, lenticular transpiration may cause some desiccation in those trees that shed their leaves at the on set of the winter. • During cold winter water absorption by roots is at a minimum, thus the importance of lenticular transpiration is increased.
- 7. SIGNIFICANCE OF TRANSPIRATION Transpiration is advantageous because: 1) It creates suction force and help in the ascent of sap. 2) It helps in the absorption of water and minerals by roots. 3) It helps in evaporating excess amount of water from moist soil. 4) It plays a role in translocation of food from one part of the plant to the other part. 5) It brings opening and closure of stomata which indirectly influences the gaseous exchange for the processes of photosynthesis and respiration. 6) It helps in dissipating the excess energy absorbed from the sun, which will otherwise raise the leaf temperature. 7) It maintains suitable temperature of leaves by imparting a cooling effect.
- 8. Transpiration is an unavoidable evil: • It is unavoidable because leaf structure (stomata) favorable for uptake of CO2 and O2 necessary for photosynthesis and respiration. At the same time, it is also favorable for the loss of water through transpiration. • Transpiration is an ‘evil’ because often it causes injury by dehydration due to heavy transpiration loss when the atmospheric conditions are aggressive such as high light intensity, hot winds, depleted soil moisture and poor water retentive capacity of soil.
- 9. STRUCTURE OF STOMATAL COMPLEX IN MONOCOT AND DICOT SPECIES : • The appearance of the guard cells differs characteristically from the surrounding epidermal cells. • The guard cells grasses (monocots) are dumbbell shaped and are associated with epidermal cells that differ in appearance from the rest of the epidermal cells. • These epidermal cells are called subsidiary cells or accessory cells. In case of dicots, the guard cells are generally bean shaped. • One other distinguishing feature of guard cell is the presence of chloroplasts. Epidermal cells do not possess chloroplasts.
- 10. INVOLVEMENT OF STOMATA IN TRANSPIRATION • The stomatal movement is understood as a direct response to increase or decrease in the osmotic potential that result from osmotic changes that cause water to move in or out of the guard cells. • If water moves in, the cells expand (become turgid); if water moves out, they go flaccid. • When the guard cells are turgid, the stoma is open; when the guard cells are flaccid, the stoma is closed. • To effect this movement of water, an exchange must takes place between the guard cells and the surrounding mesophyll and epidermal cells.
- 11. • The development of a more negative osmotic potential in the guard cells would cause of water potential gradient to develop between the guard cells and their neighboring cells. Water would diffuse in to the guard cell, causing them to become more turgid. • The development of a less negative osmotic potential in the guard cells would cause a water potential gradient to develop in the opposite direction, and water would flow out of the guard cells into the neighboring cells.
- 12. TRANSPIRATION IN RELATION TO PRODUCTIVITY: The importance of water use efficiency (WUE) in influencing grain yield under water limited conditions can be explained by the following model given by Passioura. Grain Yield = T x TE x HI T = Total transpiration by the crop canopy TE = Transpiration Efficiency or WUE HI = Harvest Index (Economic Fraction of Dry matter) This relationship provides an analytical tool to select the genotype with high levels of T and TE.
- 13. WATER USE EFFICIENCY: The water use efficiency (WUE) of field crops is defined as ‘It is the amount of dry matter produced per unit amount of water transpired’ Dry matter production (DM) WUE = ------------------------------------- Evapotranspiration WUE is expressed as g DM kg-1 water. WUE measurements can be made on plants in containers, on individual plants, and on crop communities. They can be used for economic yield as well as total dry matter calculations. water requirement is the reciprocal of WUE. Water requirements is usually expressed in weights of equal magnitude, such as g water g DM-1
- 14. Water use efficiency in C3 & C4 plants A two fold increase in WUE of C4 species when compared with C3 grasses or dicots. Water use Efficiency g DM (kg H2O) -1 for C4 and C3 species. Species Grasses Dicots C 3 1.49 1.59 C4 3.14 3.44 • The WUE of C4 species is generally higher than C3 species. • The higher WUE of C4 species is a result of higher photosynthetic rate under high light and temperature and lower transpiration rates under low light.
- 15. • The WUE values for both C3 and C4 species are low compared with CAM plants. • CAM species, pineapple (Ananas comosis), has shown a WUE of 20g DM kg-1 water. • Use of crop species with CAM is limited because the CO2 fixation and overall productivity of CAM plants is low (CAM is only a survival mechanism but not a productive mechanism).
- 17. FACTORS INFLUENCING THE WUE: 1. Climatic factors • WUE has almost an inverse relationship with Relative humidity (R.H), lower R.H. increases evapotranspiration (ET) without a corresponding increase in crop yield. • Factors such as sunlight and temperature that affect ET, rate of photosynthesis and dry matter production will either decrease or increase WUE.
- 18. 2. Agronomic practices and crop management • Early sown crops will escape the moisture stress while the delayed sowing favors heavy weed growth which creates severe competition for water, light, nutrients etc. • The crop should have an optimum crop canopy (4-6 LAI) for proper light interception. • Plant Population and plant architecture influence WUE by influencing the interception and utilization of solar energy. Depth of sowing also influences water availability and there by seedling emergence, vigor and final yield.
- 19. 3. Antitranspirants • WUE can be improved by using antitranspirants which reduces transpiration. • These antitranspirant may influence stomatal closure (Phenyl mercuric acetate, ABA, CCC , Salicylic acid etc). • Form a film (Hexadecanol, acetyl alcohol etc.) on the leaf surface or increase plant reflectivity (eg. Kaolinite) and reduce leaf temperatures.
- 20. 4. Use of mulches • Mulches are beneficial in conserving or economizing water use by plant ranging from 10-50%. • It depends upon the crop in which it is used, rainfall, wind velocity and temperature of both air and soil. • Organic mulches (straw, rice dust, saw dust etc.) light colored and light reflecting mulches reduce soil temperature. But black colored mulches such as black, grey, transparent polythene sheets and petroleum products increase temperature upto 5-80C. • Plastic mulches are costly and suitable to areas where soil temperatures are low and unfavorable to crop growth.
- 21. 5. Use of shelter belts • Shelter belts decrease the damaging effects of winds on crops and modify the micro climate. • Higher humidity and lower vapor pressure deficit prevail in shelter belt that reduces heat. This will help ultimately for higher WUE. • Increased yields due to shelter belts are reported in case of cotton, onion, sweet potato, tomato and wheat.
- 22. 6. Method and quantities of water application • Frequent light irrigations keep the soil surface wet for a longer period but consequently greater loss due to evaporation. • Heavy application of water causes heavy deep percolation losses. • Selection of proper method of irrigation is important based on soil and crop characteristics. • WUE is generally higher with sprinkler irrigation than surface method of irrigation. • Drip irrigation also increases production and decrease the water use by a crop. Among surface irrigation methods, WUE of crops increases in the order of wild flooding, border strip, check basin, basin and furrow irrigation
- 23. 7. Fertilizer application • WUE of crops invariably increases with the application of fertilizers on deficient soils under adequate soil moisture conditions. This is particularly with high yielding varieties and hybrids. 8. Weed control • Weeds due to their early establishment and a better root system are able to exhaust soil moisture more effectively than crop plants. • Therefore, both yield and WUE are reduced. Controlling weeds is essential for higher WUE of crops.