Factors Affecting the Rate of Transpiration

The rate of water uptake by a plant, also known as the rate of transpiration, can be affected by multiple environmental factors. The roots will absorb more water from the soil if the rate of transpiration increases.

There will always be transpiration taking place, but the rate of transpiration can vary. There are four main factors that affect the rate:

  • Temperature
  • Light intensity
  • Air movement
  • Relative humidity
Factor increasingEffect on the rate of transpirationExplanation
TemperatureIncreasesIf the surrounding temperature of a plant increases, more water molecules will evaporate from the mesophyll,

This increases the rate of diffusion of water from the leaf.
Light intensityIncreasesWhen the light intensity is higher, the stomata open wider to allow more carbon dioxide into the leaf for photosynthesis.

This allows more water to be lost.
Air movement (e.g. wind)IncreasesWind conditions cause the air movement around the plant to fluctuate. When the air movement increases, it removes water vapour from the air surrounding the leaf.

This creates a concentration gradient between the leaf and the air, which increases water loss.
Relative humidity – Measures the concentration of water vapour in the air compared to the total concentration of water the air can holdDecreasesThe diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by a higher concentration of water molecules (higher relative humidity). This is because the concentration gradient is lower.