16.2C: Transpiration

Definition

• Transpiration: The process of evaporation of water from plants, primarily occurring at the leaves through open stomata, necessary for photosynthesis.

Importance of Transpiration

• Pulls water from roots to leaves. Functions include:
  • Supply photosynthesis (1%-2% of total water used)
  • Transport minerals from roots for biosynthesis in leaves
  • Cool the leaf

Measuring Transpiration

• Potometer: A device used to measure the volume of water transpired by plants.

Environmental Factors Affecting Transpiration Rate

1. Light

   • Stimulates stomatal opening, increasing transpiration.
   • Light warms the leaf, enhancing evaporation.

2. Temperature

   • Higher temperatures increase evaporation, leading to greater transpiration rates.
   • Example: At 30°C, transpiration rate may be three times that at 20°C.

3. Humidity

   • Dry air increases the diffusion rate of water out of the leaf.
   • Lower humidity results in faster transpiration.

4. Wind

   • Breezes carry humid air away from leaves, replacing it with drier air, which speeds up transpiration.
   • Still air can cause humidity to build up around leaves, reducing transpiration.

5. Soil Water

   • Adequate soil moisture is crucial; if roots fail to absorb water, the plant will lose turgor and close stomata, reducing transpiration and photosynthesis.
   • Insufficient water can lead to wilting.

Water Loss in Transpiration

• Significant water loss: An acre of corn can transpire 400,000 gallons (1.5 million liters) of water in a growing season.
• This amount of water could cover the field with a lake 15 inches (38 cm) deep.