Transpiration

Definition

The passive movement of water through a plant and its evaporation from aerial surfaces, primarily via stomata in leaves. This process drives the mass flow of xylem sap, cools plant tissues through evaporative cooling, and creates the osmotic gradients that facilitate mineral nutrient uptake from roots. Transpiration rates respond to environmental humidity, temperature, wind, and soil water availability; when water stress occurs, stomatal closure reduces transpiration but concurrently limits CO₂ diffusion, thereby constraining photosynthesis and plant growth.

Etymology

From Latin 'transpirare,' to breathe through, from 'trans-' (across) + 'spirare' (to breathe).

Example

Desert beetles (Tenebrionidae) exploit transpiration-driven moisture gradients by collecting condensed fog on their elytra, while leaf-mining insects track intracellular water potential changes caused by host-plant transpiration rates to optimize feeding site selection.

Related Terms

• stomata
• Cuticle
• xylem
• water potential
• transpiration stream
• guttation
• evapotranspiration
• plant-insect interactions

Usage Notes

Distinguished from guttation, which is root-pressure-driven liquid exudation; and from evapotranspiration, the combined water loss from soil evaporation plus plant transpiration at ecosystem scales. In arthropod contexts, transpiration properly describes plants, though the term is occasionally (and less precisely) applied to evaporative water loss from animal respiratory surfaces—where 'integumentary transpiration' or 'cuticular transpiration' may appear in older literature for water loss through the cuticle.