Life Sciences, Metabolism, Plant Physiology / Principles and Exploration
Transpiration and the environment — principles and investigation
Transpiration, which is the loss of water from leaves, is influenced by the state of stomata and the surrounding environment. Compare water loss by changing leaf area, stomata opening, relative humidity, and wind speed. If we look at the effects of humidity and wind separately, we can see that it is difficult to explain the moisture movement inside and outside the leaf simply by temperature.
How does it work?
When humidity is high, transpiration decreases, and when wind and leaf area increase, it increases. Even when the stomata are closed, about 5% of the transpiration of the cuticle remains.
v = leaf area × (.05+.95×stomata opening) × (1−relative humidity) × (1+.2×wind speed)
Try this investigation
- When a branch with leaves absorbs water, air bubbles in the photometer tube move toward the branch. Also observe the stomata gaps in the leaf cross section below.
- Leaf area, stomata, and wind are fixed and losses of 50% and 80% humidity for 60 s are recorded.
- Under standard conditions, compare stomata, wind speed, and leaf area one by one.
Interpreting your results
What happens to water loss when the stomata are fully closed?
Effective opening = .05 + .95 x pore opening. If the pore opening is 0, .05 remains. The humidity effect is (1−.8)/(1−.5)=.4.
Assumptions and limitations
All moisture loss amounts and rates are virtual relative values. The wind coefficient of .2 s/m and the cutoff layer of 5% are assumed for illustrative purposes only. It is approximate that the water absorption of the photometer is equal to the amount of transpiration. Stomatal reactions due to moisture storage, light intensity, temperature, differences between species, and lack of moisture are omitted. The bubbles in the scale tube do not reset the accumulated value and anything outside the relative value of 120 is marked as out of scale.