Which factors affect the rate of transpiration in a tree?

Which factors affect the rate of transpiration in a tree?

• A. Soil type and nutrient availability
• B. Cuticle thickness, hairs, and stomata distribution
• C. Leaf color
• D. Root depth

Answer: (B)

Transpiration rate is mainly about how easily water vapor can escape from the leaf, which is controlled by leaf surface traits and stomatal behavior. The cuticle is a waxy layer on the leaf surface; when it’s thicker, it acts as a stronger barrier to water loss, so less water can diffuse out. Leaf hairs, or trichomes, influence the boundary layer—the thin layer of still air around the leaf. A thicker boundary layer can slow the diffusion of water vapor away from the leaf, reducing transpiration under many conditions. Stomata are the openings through which most transpiration occurs; their density and distribution determine how many routes there are for water to exit and how readily they can be opened or closed by guard cells in response to light, humidity, and CO2. More stomata or more open stomata mean more water loss, while fewer or closed stomata reduce transpiration. These epidermal features directly shape the pathways and ease of water loss. By comparison, soil type and nutrient availability affect water supply and overall plant water status more indirectly, leaf color isn’t a direct driver of transpiration, and root depth mainly influences access to water rather than the leaf’s rate of water loss itself.

Transpiration rate is mainly about how easily water vapor can escape from the leaf, which is controlled by leaf surface traits and stomatal behavior. The cuticle is a waxy layer on the leaf surface; when it’s thicker, it acts as a stronger barrier to water loss, so less water can diffuse out. Leaf hairs, or trichomes, influence the boundary layer—the thin layer of still air around the leaf. A thicker boundary layer can slow the diffusion of water vapor away from the leaf, reducing transpiration under many conditions. Stomata are the openings through which most transpiration occurs; their density and distribution determine how many routes there are for water to exit and how readily they can be opened or closed by guard cells in response to light, humidity, and CO2. More stomata or more open stomata mean more water loss, while fewer or closed stomata reduce transpiration.

These epidermal features directly shape the pathways and ease of water loss. By comparison, soil type and nutrient availability affect water supply and overall plant water status more indirectly, leaf color isn’t a direct driver of transpiration, and root depth mainly influences access to water rather than the leaf’s rate of water loss itself.