Question

why stomata occurs on lower surface in dorsiventral leaf

Answer 1

The stomata present on lower surface of dorsiventral leaf because the evoparation of water in plant will be less on lower surface. As the leaf is not directly exposed to sunlight . Hence in many plants the leaves have stomata on the lower surface.
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Answer 2

To limit the loss of water through transpiration

Because if the leaves are present on the upper surface the loss of water will be increased which will cause shrinkage of leaf.