How does sunken stomata reduce water potential gradient?

It makes the water harder to get out of the plant by diffusion, thus trapping water vapor in the space. The trapped humidity makes water on the surface of spongy cells harder to evaporate.

I think it's:
- sunken stomata are in depressions
- the depressions make it difficult for air movement/wind to remove the vapour, it being a factor
- the water potential outside leaf has increased
- reduced water potential gradient
- reduced rates of transpiration

Or something along those lines.

edit: just imagine pits.
Then water isn't removed by wind.
So water potential isn't decreased (is higher than otherwise)
So there's a reduced water potential gradient between environment and air spaces in leaf
So there's less transpiration

Thanks for the reply. Why is the water potential outside the leaf increased? Can i think of it as that there are less water molecules in the air as they are trapped hence the water potential is higher in the air. And the sunken stomata have a lower water potential energy ? And what does it mean by reducing the water potential gradient ?

A sunken stomata means that the stomata is in a pit. The wind going past can't remove the water as it is in a pit, like imagine wind going under the leaf, but it wouldn't affect the water in the pit. So the pit traps moist air (already transpired I presume.) This means that the outside has a higher water potential than otherwise.

Water moves from a high water potential to a low water potential. If you decrease the gap between the two water potentials, you're decreasing the water potential gradient. Very much like concentration gradient.

As it's the same principle as with concentration gradient, look at this diagram:

If you increase the concentration in lungs or decrease the concentration in blood, you make the like less steep, decreasing the gradient. Does that make sense?

It does make sense. So stomata have a lower water potential energy as it traps the moist air and the outside has a higher water potential energy as it has less water molecule. Is that right ? So the outside now has a high water potenital and the inside now has low water potential. But the two water potential energies are quite close thats why the concentration gradient is decreased. Is this right ?

edit:
water goes from ↑Ψ → ↓Ψ
If you decrease the gap between the water potentials, you decrease the Ψ gradient.
end of edit

It's the other way round:
- water moves down water potential gradient, from high to low.
- water moves from high water potential in air space in leaf to low water potential in environment
- to reduce the water potential, the stomata are in pits "sunken stomata"
- pit traps moist air, so has a higher water potential than if the pit wasn't sunken (as wind doesn't remove the water)
- as water goes from high to low, and you've made the low water potential outside higher, there's a lower water potential gradient
- so there's less transpiration

in summary
- pit traps moist air
- so increased water potential outside (in pit)
- so decreased water potential gradient
- so less transpiration

(That's the most you're going to need, I think.)

(Included in edit: It'd be far easier to explain in person, unfortunately I can't do that. :/)