Transpiration

Water loss, i.e. transpiration, in xerophytic (desert) and non-xerophytic (non-desert) plants is dependent

on different environmental conditions.

Xerophytes or xerophytic plants are plants which have adapted to conditions of unfavourable water balance, conditions where the rate of water loss is potentially greater than the availability of water, as in the case of desert plants. These types of plants have developed a wide range of features known as xeromorphic features which reduce the rate of water loss, these adaptations can take place in other plants too but more concentration on these changes taking place in xerophytes will be put. Non-xerophytes are those that arenЃft adapted in any particular way, like the xerophytes, for the prevention of too much water loss but are just normal plants and mostly those grown by individuals under proper conditions.

Water loss is actually a process known as transpiration. Transpiration is the process by which plants lose water as water vapour into the atmosphere. Most of this loss takes place through leaves and the whole experiment will be based on leaves of xerophytes and non-xerophytes.

The significance of transpiration is as the following: transpiration is the consequence of photosynthesis which seems to take place as for photosynthesis carbon dioxide is required and a leaf permeable to carbon dioxide is permeable to water vapour as well. Therefore evaporation of water must then accompany photosynthesis and this produces effects which may be beneficial to the plant.

The transpiration stream is dependent

on the rate of evaporation from leaves and is the flow of water brought about when evaporation of water from leaf cells causes their turgor to fall and the concentration of their cell sap rises increasing the water potential. Cells are caused to atke

up water from their neighbours and xylem vessels. Withdrawal of water by osmosis from the xylem vessels produces a tension. This tension draws water up the vessels of the stem from the roots bringing about the transpiration stream.

Conditions are present which affect the transpiration rate and are as follows:

Ѓњ Light intensities affect in the following way: when light intensities increase, the stomata on both leaf surfaces open allowing more rapid evaporation.

Ѓњ In decreased light intensities the stomata are closed except only a few and in this condition evaporation is reduced by a great deal.

Ѓњ In humid conditions, when the atmosphere is already saturated with water vapour, not much water can be absorbed from plants thus reducing transpiration.

Ѓњ In dry atmosphere, transpiration is more rapid as the surrounding air has almost no water and readily takes up water from the leaves.

Ѓњ In warm conditions (varying temperatures) evaporation occurs rapidly, direct sunlight without a warm atmosphere also has this effect as the leaf absorbs energy raising the temperature.

Ѓњ In cool temperature or high temperatures the capacity of the air to hold water vapour increases and so transpiration increases.

Ѓњ In still air, the region around the leaf becomes saturated with water vapour and no more can be absorbed from the leaf, transpiration is therefore reduced.

Ѓњ In moving air,