Explain: (a) the effects of wind speed, and the variation of temperature, humidity and light intensity on transpiration rate (b) how wilting occurs

Sourav PanNovember 2, 2024

Answered

To understand the effects of environmental factors on transpiration rate and how wilting occurs in plants, we can break down the information into two main sections: (a) the effects of wind speed, temperature, humidity, and light intensity on transpiration, and (b) the process of wilting.

(a) Effects of Environmental Factors on Transpiration Rate

1. Wind Speed:
   • Increased Transpiration: Higher wind speeds can increase the rate of transpiration. Wind removes the water vapor that accumulates around the leaf surface, maintaining a lower humidity level near the stomata. This enhances the concentration gradient between the inside of the leaf (high humidity) and the outside air (lower humidity), promoting faster diffusion of water vapor out of the leaf.
   • Implications: In windy conditions, plants may lose water more quickly, which can lead to increased stress if water is not replenished.
2. Temperature:
   • Increased Transpiration: Higher temperatures generally increase transpiration rates. Warmer air holds more moisture, and increased temperatures raise the kinetic energy of water molecules, leading to more rapid evaporation from mesophyll cells into air spaces.
   • Limitations: However, if temperatures become excessively high, plants may close their stomata to conserve water, which can reduce transpiration rates.
3. Humidity:
   • Decreased Transpiration: High humidity levels in the surrounding air reduce the concentration gradient for water vapor between the inside of the leaf and the external environment. As a result, transpiration rates decrease because there is less driving force for water vapor to diffuse out of the stomata.
   • Dry Conditions: Conversely, low humidity increases transpiration as it enhances the concentration gradient.
4. Light Intensity:
   • Increased Transpiration: Light stimulates photosynthesis and causes stomata to open for gas exchange (CO₂ uptake). When stomata are open, water vapor can escape more readily, increasing transpiration rates.
   • Photosynthesis Link: The relationship between light intensity and transpiration is often linked to photosynthetic activity; higher light levels promote both processes.

Summary of Transpiration Factors

In summary, wind speed and temperature generally increase transpiration rates by enhancing evaporation and maintaining concentration gradients. In contrast, high humidity decreases transpiration rates by reducing this gradient. Light intensity also promotes transpiration by causing stomata to open during photosynthesis.

(b) How Wilting Occurs

Wilting is a physiological response in plants that occurs when they lose more water than they can absorb. Here’s how this process unfolds:

1. Water Loss Exceeds Absorption:
   • Wilting typically occurs due to excessive transpiration under conditions such as high temperatures, strong winds, or low humidity. When these factors lead to significant water loss from leaves through stomata, turgor pressure in plant cells decreases.
2. Turgor Pressure Decline:
   • Turgor pressure is the pressure exerted by water inside plant cells against their cell walls. It is essential for maintaining cell rigidity and overall plant structure. When plants lose water rapidly, turgor pressure drops, causing cells to become flaccid.
3. Physical Symptoms:
   • As turgor pressure decreases, leaves may droop or fold up to reduce surface area exposed to sunlight and minimize further water loss through transpiration. This adaptation helps conserve moisture but compromises photosynthetic efficiency.
4. Long-Term Effects:
   • If wilting persists due to prolonged drought or inadequate water supply, it can lead to permanent damage or even death of plant tissues. Continued wilting can weaken plants and make them more susceptible to pests and diseases.
5. Recovery Potential:
   • Many plants can recover from temporary wilting if watered promptly; they will regain turgidity as they absorb water again. However, if wilting is prolonged or severe, recovery becomes less likely.

Summary of Wilting

In summary, wilting occurs when plants lose more water through transpiration than they can absorb from their roots. This leads to decreased turgor pressure in cells, resulting in drooping leaves as a mechanism to reduce further water loss. Prolonged wilting can cause serious damage or death to plants if not addressed.