Abstract
The stomatal response to evaporative demand depending on air humidity and wind was analyzed in an intact cucumber leaf (Cucumis sativus L.) exposed to different conditions of air humidity and wind velocity in a leaf cuvette. The evaporative demand on the transpiring leaf was evaluated on the basis of the environmental factors within the leaf cuvette and was set at different values by changing the saturation vapor deficit and wind velocity within the leaf cuvette. Using a model leaf of wetted filter paper, a constant positive linear relationship was found between the evaporation rate and the evaporative demand even under different conditions of air humidity and wind velocity. On the other hand, the relationship between gas exchange parameters in the cucumber leaf (i.e., stomatal conductance, transpiration rate and photosynthetic rate) and the evaporative demand was discontinuously shifted due to the change in wind velocity even under the same humidity condition. These differences in the stomatal behaviors in relation to the evaporative demand, given by the respective changes in air humidity and wind velocity, were not attributed to the feedback stomatal response to the intercellular CO2 concentration in the leaf. The mechanism of stomatal response to the evaporative demand, given by the respective changes in air humidity and wind velocity, was explained on the basis of the antagonism relationship between the guard and epidermal cell turgors that are directly affected by the leaf surface humidity and impact of the evaporative demand through water balance within the stomatal complex.
