In what type of environment..?

Question

would a plant have stomata on the upper surface of the leaf? and why

thank you

Answer 1

The disadvantage to having stomata on your upper surface is that water loss becomes too great while trying to absorb CO2. This is because the upper surface is usually the warm side - it faces the sun and gets most of it's radiation.

If you're in an area where water loss isn't much of an issue (such as a very humid, warm rainforest or underwater) then it becomes adventitious to have as many stomata as possible to maximize CO2 uptake - this includes the upper surface.

Aquatic plants have stomata on their upper surface because gas exchange is poor on the water side, and non-xylary moisture is generally unwanted.

There are lots of other adaptations to it. I remember reading once that CAM cacti have stomata on both surfaces because they don't bother opening them up during the day at all, which removes the effect of a warmer adaxial surface.

In the end it depends a lot on ecology, environment, and weather. Plants are in a constant battle to minimize water loss and maximize CO2 uptake, and stomatal morphology often reflects that.

Answer 2

Think about this logically - the plant has stomata to release water vapor.

Most (horizontal) leaves have stomata on the underside of the leaf, where they're protected from rain.  If a leaf is vertical, such as an iris, cattail, or blade of grass, there may be similar numbers on both sides.

Having stomata on the underside is a disadvantage if the air beneath is already saturated with moisture (makes it harder for the water to evaporate).

This mostly happens when the leaf is horizontal, and there's more moisture beneath the leaf (as in aquatic plants with floating leaves, such as  water lilies).