Why does light cause an increase or decrease in transpiration in a plant?

Question

I'm lost! Thanks!

Answer 1

Generally light will cause an increase in transpiration in leaves.  This is for two reasons.  First, light causes stomates to open (these are little pores on the surfaces of leaves that connect the inside of the leaf to the atmosphere).  Second, intense light will cause the leaf to warm up.  This increases the water vapor pressure inside the leaf so that the gradient in water vapor pressure between the inside and outside of the leaf is steeper.  This will speed up the diffusion of water vapor out of the leaf.