Factors Affecting Transpiration in Plants

 

Factors Affecting Transpiration in Plants

Different factors affecting the rate of transpiration are:

Cellular Factors

The cellular factors affecting the rate of transpiration are:

1. The orientation of leaf,
2. The water status of the plant,
3. Structural Peculiarities of the leaf,
4. Total number and distribution of stomata in a leaf.

Environmental Factors

The environmental factors affecting the rate of transpiration are:

1. Light,
2. Humidity,
3. Temperature,
4. Atmospheric pressure,
5. Wind speed or velocity.

Relative Humidity

The amount of water vapour present in the air at a particular time and temperature is expressed as a percentage of the amount required for saturation at the same temperature. The rate of transpiration is inversely proportional to relative humidity. More the relative humidity less is the transpirate rate.

Temperature

A high temperature lowers the relative humidity and opens the stomata even in darkness. As a result, the rate of transpiration increases.

Light

The stomata open during the day and close in the dark. Presence of light is directly proportional to the rate of transpiration.

Air

If the air is still, the transpiration rate is low. This is because the water vapour accumulates around the transpiring organs and reduce the diffusion pressure deficit of the air.

If the air is moving, the saturated air around the leaves is removed and the transpiration rate increases.

Water Availability

The transpiration rate is directly proportional to the absorption of water by the roots from the soil. A decrease in water absorption causes the closure of stomata and wilting, thereby reducing the rate of transpiration.

Surface Area of the Leaves

A leaf having more surface area will show more transpiration rate than the leaf with a lesser surface area.

Ascent of Saps

When water evaporates through the leaves, a pull is created through the xylem, and water moves back to the leaves. This is known as the transpiration pull.

The ascent of sap that is driven by transpiration depends on the following properties of water:

• Cohesion – This is the mutual attraction between molecules of water.
• Adhesion – The attraction of water molecules towards polar surfaces.
• Surface tension – The molecules of water are more attracted to each other in the liquid phase than in the gas phase.

Opening and Closing of Stomata

Stomata consist of a pair of guard cells with an aperture in between. It remains open during the daytime and is closed at night. The reason for the opening and closing of this structure is the turgidity of guard cells.

The interior wall of the guard cells present towards the aperture is dense and flexible. The stomata open when the turgidity of the guard cells increases. The exterior walls bulge out, and the interior walls form a crescent shape.

The orientation of the microfibrils in the guard cells also plays an important role in the opening of the stomata. The radial orientation of the microfibrils makes it easier for the stomata to open. The stomata close when the turgidity of the guard cells decreases due to the water loss and the interior walls form a crescent shape retrieve their original shape.

In dicots, the lower side of leaves have more stomata while in monocots, both the sides have an equal number of stomata.