Difference Between Stomatal Conductance and Transpiration

The key difference between stomatal conductance and transpiration is that stomatal conductance is the rate of CO2 entering or water existing through the stomata of leaves, while transpiration is the water movement through a plant and its evaporation from aerial parts of the plant such as leaves, stems, or flowers.

The plant water relationship is concerned with how plants manage the hydration of their cells. This includes the collection of water from the soil, water transport within the plant, and water loss by evaporation from the leaves. The water status of plants is usually expressed as water potential. Stomatal conductance and transpiration are two important phenomena for plant water status.

CONTENTS

1. Overview and Key Difference
2. What is Stomatal Conductance 
3. What is Transpiration
4. Similarities – Stomatal Conductance and Transpiration
5. Stomatal Conductance vs Transpiration in Tabular Form
6. Summary – Stomatal Conductance vs Transpiration

What is Stomatal Conductance?

Stomatal conductance is defined as the rate of CO2 entering or water existing through the stomata of leaves. It is also a measure of the degree of stomatal opening that can be used as an indicator of plant water status. Generally, stomatal conductance is measured by a porometer. The inverse of stomatal conductance is known as stomatal resistance. Stomatal conductance is directly under the biological control of the leaf through its guard cells. These guard cells surround the stomatal pore. The turgor pressure and osmotic potential of guard cells directly influence stomatal conductance.

Figure 01: Leaf Porometer

Stomatal conductance is also a function of stomatal density, stomatal aperture, and stomatal conductance. It is even essential to leaf level calculation of transpiration. Furthermore, it has been shown in many studies there is a direct correlation between the use of herbicides and changes in physiological and biochemical growth processes in plants. The use of herbicides mainly results in a reduction in stomatal conductance and turgor pressure in leaves. The stomatal opening is normally light dependant. There are two key elements involved in the process. They are the stomatal response to blue light and the photosynthesis in the chloroplast of guard cells. Both these key elements decrease the osmotic potential of guard cells, which causes water to flood into the cells. Therefore, the guard cells become enlarged and open. Furthermore, some research studies have also found the relationship between drought stress and stomatal conductance.

What is Transpiration?

Transpiration is the water movement through a plant and its evaporation from aerial parts of the plant such as leaves, stems, and flowers. Only a small amount of water taken up by the root is used for the growth and metabolism of the plants. The remaining unused water is lost through transpiration and guttation. Transpiration occurs through stomatal apertures. It is known as a necessary cost associated with the opening of the stomata, which allows the diffusion of CO2 gas from air for photosynthesis. The potometer measures the rate of transpiration.

Figure 02: Transpiration

The transpiration process cools the plants. It also changes the osmotic pressure of cells that enables mass flow of mineral nutrients and water from roots to shoots. The hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil are the major two factors influencing the rate of water flow from the soil to the roots. Moreover, the mass flow of liquid water from roots to the leaves is influenced primarily by water potential differences and capillary action.

What are the Similarities Between Stomatal Conductance and Transpiration?

• They are two processes that take place through stomatal apertures.
• Both processes influence the water status of a plant.
• These processes are encouraged by light.
• Both processes can be measured.
• They are both extremely important for the survival of plants.

What is the Difference Between Stomatal Conductance and Transpiration?

Stomatal conductance is the rate of CO2 entering or water existing through the stomata of leaves. In contrast, transpiration is the process of water movement through a plant and its evaporation from aerial parts of the plant such as leaves, stems, or flowers. So, this is the key difference between stomatal conductance and transpiration. Moreover, in stomatal conductance, the water moves from stomata to the atmosphere, but in transpiration, the water first moves from roots to stomata and then to the atmosphere.

The following infographic presents the difference between stomatal conductance and transpiration in tabular form.

Summary – Stomatal Conductance vs Transpiration

The water status of plants is extremely important for their survival. Stomatal conductance and transpiration are two important phenomena for plant water status. Stomatal conductance is a measure of the degree of stomatal opening that can be used as an indicator of plant water status. It is also known as the rate of CO2 entering or water existing through the stomata of leaves. Transpiration is the loss of water from aerial parts of the plant in the form of water vapor. Thus, this is the summary of the difference between stomatal conductance and transpiration.

Reference:

1. “Stomatal Conductance, Photosynthesis, and Transpiration, Modeling.” SpringerReference, doi:10.1007/springerreference_224109.
2. “Transpiration – What and Why?” Passel.

Image Courtesy:

1. “Leaf porometer” By International Maize and Wheat Improvement Center (CC BY-NC-SA 2.0) via Flickr
2. “salz und transpiration” By s gendera (CC BY 2.0) via Flickr

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