Question

what do you mean by aerenchyma

Answer 1

a soft plant tissue containing air spaces, found especially in many aquatic plants

Answer 2

The Aerenchyma is a spongy tissue that forms of air channels in the leaves, allows exchange of gases between the shoot and the root form the channels of air-filled cavities.

You have to provide a low-resistance internal pathway and exchange of gases such as oxygen plant above the water and the submerged tissues from the hypoxic soils.