Introductory Crop Physiology

Mechanism of water absorption

In higher plants, water is absorbed through root hairs that are in contact with soil water and form a root hair zone a little behind the root tips. Root hairs are tubular hair like prolongations of the cells of the epidermal layer (when epidermis bears root hairs, it is also known as piliferous layer) of the roots.
The walls of root hairs are permeable and consist of pectic substances and cellulose which are strongly hydrophilic in nature. Root hairs contain vacuoles filled with cell sap. When roots elongate, the older root hairs die and new root hairs are developed so that they are in contact with fresh supplies of water in the soil. Kramer (1949) proposed that water is absorbed by two mechanisms.

1. Active absorption of water

In higher plants, water is absorbed through root hairs that are in contact with soil water and form a root hair zone a little behind the root tips. Root hairs are tubular hair like prolongations of the cells of the epidermal layer (when epidermis bears root hairs, it is also known as piliferous layer) of the roots.

(a) Osmotic absorption: Water is absorbed from the soil into the xylem of the roots according to osmotic gradient.
(b) Non-osmotic absorption: Water is absorbed against the osmotic gradient.

2. Passive absorption of water

It is mainly due to transpiration; the root cells do not play active role and remain passive.