What speeds up or slows down transpiration?

Transpiration = water vapour diffusing out through the stomata · rate depends on how open the stomata are and how steep the water-vapour gradient is · change one factor at a time

Conditions around the leaf

Light intensity 70%

Temperature 25 °C

Humidity 50%

Wind speed 2.0 m/s

Transpiration rate

Stomata open

Water-vapour gradient

Leaf cross-section (not to scale)

Potometer: bubble movement in 1 minute

Change one factor and watch the rate.

Higher humidity lowers the rate
Wind raises the rate
Closed stomata: the rate drops