Light :- Light influences transpiration in 2 ways, sunlight falling on the leaf will increase its temperature hence evaporation of water as well. Light influences the guard cells to open the stomata and thus increase the rate of transpiration.
First of all, what is Transpiration?
This is the process by which water is evaporated in the surrounding through the leaf surface(with the help of the stomatal pores) of the plant. This is the same as in plants as Sweating in Humans.
Now, the question is how the evapotation occurs. The air that surrounds the leaf surface takes away with it the moisture evaporating from the leaf. This happens to maintain the water balance/ equilibrium in the plant.
This equilibrium is maintained by absorbing the required water from soil by the roots, and evaporating the excess water into the surrounding by leaf surface.
1. Temperature of surrounding:
If the temperature outside is very high, as in summers, the air surrounding the leaf is hot and so the evaporation will be more. transpiration will be more.
If the temp. is low as during winters, evaporation is comparatively less.
* In condition of very high temperature stomatal pores gets close and stops the transpiration to prevent dehydration eg. in Deserts.
2. The motion of wind:
If the wind is blowing normally, the process of transpiration is normal.
But if the wind is blowing fast, the process of transpiration increases as the water vapours in the air surrounding the leaf is blown away by fast moving wind with high frequency. Hence increasing the evaporation.
3. Water content in the surrounding i.e. Humidity:
If the wind is humid, transpiration will be very low. There is no water deficit in surrondings, so no diffusion of water in the surronding is needed. Supporting to this, absorption of water from roots will also be less.
4. Leaf surface:
The transpiration is low from the inner surface of leaf while high from outer surface.
The transpiration is different in leaves of different shapes. Like the leaf which is broad will have more transpiration comparative to the needle shape leaves.
Since most water loss occurs through stomata, their structure, frequency, distribution and opening and closing greatly influence the rate of transpiration.
Several other factors such as relative humidity of the atmosphere, velocity of wind, light intensity, temperature and soil conditions also affect transpiration.
Besides these environmental factors, the structural features (known as internal factors), habit and habitat of the plant also influence the rate of transpiration.
Decrease in leaf surface, rolling of leaves during drought, absence of leaves, and presence of epidermal hairs and sunken stomata decrease, restrict or prevent transpiration.
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