(A) External factors
1. Atmospheric humidity:
If atmosphere is humid, it reduces the rate of transpiration. When the air is dry, the rate of transpiration increases.
A high wind speed or a dry breeze will greatly increase transpiration.
3. Atmospheric pressure:
Low atmospheric pressure increases the rate of transpiration.
4. Soil temperature:
Plants growing in warm regions exhibit less transpiration at a temperature lower than 5 – 8°C.
5. Air temperature:
The rate of evaporation doubles with every rise in temperature by 10°C. High temperature affects the closure of stomata, reduces transpiration.
Less amount of soil water decreases the rate of transpiration. If the rate of transpiration exceeds the rate of absorption, the stomata get closed and plant wilts.
(B) Internal Factors
1. Leaf structure:
Presence of thick cuticle and sunken stomata reduces the rate of transpiration.
2. Leaf orientation:
Transpiration is low in north-south orientation as compared to other orientation.
3. Leaf area:
Directly proportional to the transpiration rate.
4. Plant age:
Germinating seeds exhibit a slow rate of transpiration. It becomes maximum at maturity and decreases at senescence stage.
5. Root shoot ratio:
The increase in ratio of root and shoot enhances the rate of transpiration.
6. Water contents of the leaves:
Directly proportional to the rate of transpiration.