Transpiration and Photosynthesis a compromise. Give explanation.

Explanation

Transpiration has more than one purpose.
It creates transpiration pull for absorption and transport of plants.
Supplies water for photosynthesis.
It cools leaf surfaces, sometimes 10 to 15 degrees by evaporative cooling.
Maintains the shape and structure of the plants by keeping cells turgid.
Photosynthesis : An actively photosynthesising plant has an insatiable need for water. Photosynthesis is limited by available water which can be swiftly depleted by transpiration.
The humidity of rainforests is largely due to this vast cycling of water from root to leaf to atmosphere and back to the soil.
The evolution of the `C_4` photosynthetic system is probably one of the strategies for maximising the availability of `CO_2` while minimising water loss.
`C_4` plants are twice as efficient as `C_3` plants in terms of fixing carbon (making sugar).
However a `C_4` plant loses only half as much water as a `C_3` plant for the same amount of `CO_2` fixed.