Factors Effecting Transpiration Rates

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Explain how the abiotic factors light, temperature, wind and humidity affect the rate of transpiration. The stomata are the pores in the leaf that allow gas exchange where water vapour leaves the leaf and the carbon dioxide enters the leaf. Special cell’s known as guard cells control each pore’s opening or closing. When stomata are open transpiration rates increase. When the stomata is closed the transpiration rate decreases. Now another layer that the water has to go through is the motionless layer or the boundary layer. The larger the boundary layers the slower the rate of transpiration. Another feature is the waxy cuticle. Now this cuticle is hydrophobic which means it is water repelling. Therefore water does not move through it very easily. Thicker the cuticle slower the rate of transpiration. Abscisic acid is a single organ unlike the auxins. It stimulates the closure of the stomata during transpiration. This is as the amount of water increases the amount of Abscisic acid produced also deeply increases. FACTORS AFFECTING TRANSPIRATION

1) Light – the stomata are triggered to open in the light because of the light dependent process of photosynthesis. Now the stomata are open because they need to absorb CO2. So even low levels of light can make the stomata open. Now when the stomata open the take in CO2 but at the same time they release water. Thus the greater the light intensity the more the stomata will open which will increase the water loss and increase transpiration rate. Also if there is water on the leaves the sunlight and the heat will evaporate the water from the surface. 2) Temperature- this is a vital factor as it “drives” the water out of the plant. As the temperature increases the water holding capacity of the air around it increases. Warmer air can hold more water than cooler air can. As a result warmer air makes it less humid. Thus decreasing the water content in the air. Therefor warm air will increase the driving force for...
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