Transpiration is affected greatly by the environment factors such as temperature, light relative humidity, wind, and so on.
It is difficult, however, to determine the effect of individual factors strictly in the field condition, because in nature it is not possible to change one factor without changing other factors.
Therefore, in order to clarify the relationship between the transpiration and environment factors, it is necessary to carry out the experiments in a control cabinet which is capable to produce a definite environment condition without changing other factors.
From this view point, effect of environmental factors such as air temperature, relative humidity and wind velocity upon transpiration were studied from the aspect of the energy exchange, using a newly devised experimental apparatus.
As the material for experiment, Phaseolus vulgaris was used, and the following results were obtained.
- Transpiration increases with increasing air temperature and wind velocity.
At constant temperature and wind velocity, transpiration rate is governed by moisture content of air.
Transpiration also increases with decreasing relative humidty at constant wind velocity.
These relationships are represented by sigmoidal curves.
- Total heat energy in air is increased with increasing transpiration rate at any wind velocity tested.
Most of energy is changed as latent heat in the range of wind velocities from 0.9m. sec-1 to 1.6m.sec-1.
In a lower wind velocity such as 0.4m. sec-1, however, part of energy is changed as sensible heat, and this heat is decreased in contrast to an increase in latent heat.
From these results, it may be concluded that transpiration and the resulting energy exchange in the biosphere is remarkably affected by the surrounding factors such as air temperature, relative humidity, and wind velocity.