Factors Affecting Transpiration: Definition, Factors, and Significance

Factors Affecting Transpiration: We are all familiar with the process of transpiration that occurs through the stomata in leaves. Numerous factors influence transpiration rate, which can be classified as external or internal. We will discuss everything on the transpiration process, factors affecting transpiration, the transpiration of plants, and more in this article.

Transpiration is perceived as a necessary evil for plants because it allows them to absorb water and minerals from the soil; however, excessive transpiration can be extremely harmful to the plant, even leading to death due to dehydration. Transpiration is a natural process. So, in this article, let us now look at the various external and internal factors that influence the transpiration of plants.

What is Transpiration?

Transpiration is defined as the process of loss of water in the form of water vapour from the aerial parts of the plant through the stomata, lenticels, and cuticles.

Factors Affecting Rate of Transpiration

The rate of transpiration depends on certain factors, which are categorized into two types:

1. External Factors
2. Internal Factors

External Factors or Environmental Factors for Transpiration Process

External factors refer to the environmental factors that affect the rate of transpiration which are as follows:

(i) Atmospheric Humidity

Atmospheric humidity refers to the amount of water vapor present in the air. If the air is saturated with water vapor, the rate of transpiration decreases, and as the air becomes dry, the rate of transpiration increases. Thus, the rate of transpiration is inversely proportional to atmospheric humidity.

Fig: Rate of Transpiration vs. Humidity

(ii) Temperature

The rate of transpiration increases with the increase in the temperature of the atmosphere as it is directly proportional to the temperature. Increased temperature not only helps in quicker evaporation of the water molecules but also keeps the air warm to hold more water vapours than cold air. But at higher temperatures, wilting takes place in plants that results in a decrease in the rate of transpiration.

Fig: Rate of Transpiration vs. Temperature

(iii) Light

Bright light is the main stimulus that causes the stomata to open, because of which the plants show a daily periodicity of transpiration rate. The mode of action of light is both direct and indirect. The increase in the intensity of light raises the temperature of the leaf cells and thus increases the rate at which the liquid water is transformed into vapours. Thus, the rate of transpiration is directly proportional to the intensity of light. But at a higher light intensity, the number of heat increases which increases the temperature, thus resulting in the wilting of plants, which causes a decrease in the rate of transpiration.

Fig: Rate of Transpiration vs. Light Intensity

(iv) Wind Velocity

Fast-moving air currents continuously bring fresh, dry masses of air in contact with leaf surfaces that carry water vapor produced during transpiration and thus increase the rate of transpiration. Thus, the velocity of wind greatly affects the rate of transpiration.

Fig: Rate of Transpiration vs. Wind Velocity

(v) Soil Water Content

The availability of water in soil greatly affects the rate of transpiration. If little water is available to the plants, then it results in the dehydration of the leaf, causing stomatal closure in the mechanism of stomatal transpiration, which decreases the rate of transpiration. This condition usually occurs during drought or when the soil is frozen or at such a low temperature that roots are unable to absorb water.

(vi) Atmospheric Pressure

The rate of transpiration is inversely proportional to the atmospheric pressure. With the decrease in the atmospheric pressure, the rate of transpiration increases because the air can move out of the plant easily due to the development of pressure deficit.

Internal or Structural or Plant Factors

Internal factors include the structural factors of the plant that affect the rate of transpiration which are as follows:

(i) Leaf Surface Area

The rate of transpiration is faster if the surface area of the leaf is more. But the rate of transpiration per unit surface area is more in smaller leaves than in larger leaves because of the higher number of stomata in smaller leaves. However, the rate of transpiration per unit leaf surface area decreases in a canopy because of the density of foliage, shading effect, and decrease of air movement inside the canopy.

(ii) Leaf Structure

It includes the following features:

• a) The thickness of the cuticle: Cuticular transpiration decreases with the thickness of the cuticle.
• b) Number and position of stomata: The rate of transpiration depends on the number and position of stomata because, in dicots, the number of stomata is more at the lower surface while the isobilateral monocot leaves possess an equal number of stomata on both surfaces.
• c) Sunken stomata: The presence of sunken stomata in the leaves of succulent xerophytes reduces the rate of transpiration as it provides an area where little movement of air occurs.
• d) Hair: The hair insulates the surface of the leaf from air currents and air temperature, thus reducing the rate of transpiration.
• e) Mesophyll: The presence of a compact mesophyll layer having more palisade tissue and fewer intercellular spaces reduces the rate of transpiration, while the presence of a loose mesophyll layer having more spongy tissue and larger intercellular spaces increases the rate of transpiration.
• f) Leaf Modifications: The formation of prickles, leaf spines, scaly leaves, phyllodes, phylloclades (modifications found in xerophytes) reduces the rate of transpiration.

(iii) Root-Shoot Ratio

An extensive root system is more efficient in water uptake from the soil. Increased availability of water increases the rate of transpiration. Thus, a low root-shoot ratio decreases the rate of transpiration, whereas a high root-shoot ratio increases the rate of transpiration. Thus, the rate of transpiration is directly proportional to the root-shoot ratio.

(iv) Orientation of Leaves

Leaves arranged transversely on the shoot lose more water as they are exposed to direct sunlight, whereas if the leaves are arranged perpendicularly on the shoot, then the rate of transpiration decreases.

(v) Mucilage and Solutes

The presence of mucilage and solutes decreases the rate of transpiration by holding water tenaciously.

(vi) Hormones

The presence of the hormone abscisic acid (ABA) in the leaves of the plant regulates the stomatal movement to prevent water loss by transpiration. Thus, the accumulation of abscisic acid decreases the rate of transpiration.

Significance of Transpiration Process

The significance of transpiration are as follows:

1. It helps in the production of a suction force that helps in the conduction of water and minerals in the plants.
2. It helps to maintain the water balance.
3. It helps the cells to maintain osmosis by keeping them turgid.
4. It provides a cooling effect to the plants due to the loss of water in the form of water vapor.
5. It indirectly helps in the growth of the plant.

Summary of Factors Affecting Rate of Transpiration

Thus, transpiration is a process in which the plant loses the extra water in the form of water vapour from the aerial parts of the plant. Transpiration helps in the elimination of excess water. It is an inevitable process and a necessary evil. The factors affecting the rate of transpiration are divided into two types- external and internal factors. External factors include atmospheric humidity, temperature, light, wind velocity, soil water content, atmospheric pressure, carbon dioxide concentration in the atmosphere, and the internal factors include leaf area, leaf structure, root-shoot ratio, the orientation of leaves, and presence of mucilage, hormones, and other solutes.

FAQs on Factors Affecting Transpiration

Here we have provided some frequently asked questions on Factors affecting transpiration:

Q.1. What is transpiration?
Ans: Transpiration is defined as the process of loss of water in the form of water vapour from the aerial parts of the plant through the stomata, lenticels, and cuticles.

Q.2. What are the two types of factors affecting transpiration?
Ans: The two types of factors affecting transpiration are:
1. External or Environmental Factors
2. Internal or Structural or Plant Factors

Q.3. What are the internal factors affecting transpiration?
Ans: The internal factors affecting transpiration include leaf area, leaf structure, root-shoot ratio, the orientation of leaves, and the presence of mucilage, hormones, and other solutes.

Q.4. What are the external factors affecting transpiration?
Ans: The external factors affecting transpiration include atmospheric humidity, temperature, light, wind velocity, soil water content, atmospheric pressure, and carbon dioxide concentration.

Q.5. What is the significance of transpiration?
Ans: The significance of transpiration are as follows:
1. It helps in the production of a suction force that helps in the conduction of water and minerals in the plants.
2. It helps to maintain the water balance.
3. It helps the cells to maintain osmosis by keeping them turgid.
4. It provides a cooling effect to the plants due to the loss of water in the form of water vapour.
5. It indirectly helps in the growth of the plant.

We hope you find this article on ‘Factors Affecting Transpiration‘ helpful. In case of any queries, you can reach back to us in the comments section, and we will try to solve them. Stay tuned with Embibe for more topics and their explanation.