Stomatal Movement and Water Relations in Crops : 3. Behavior of stomata and transpiration in tobacco plant during and after drought with the aid of recording apparatus

[摘要] Qualitative changes in apparent stomatal aperture and transpiration rate of two potted tobacco plants (Nicotiana tabacum L. var. Bright Yellow) after topping were simultaneously measured with porometers and balances by which continuous recording were enabled (fig. 1). The experiment was conducted in the growth cabinet under the conditions of the illumination of 8800 lux from 9.00 a.m. to 5.00 p.m. and of other meteorological factors as mentioned in fig. 2. One plant was stopped watering during 12 successive days and, after severe wilting, rewatered sufficiently. Another plant was well watered every day to compensate the transpiration. 1. Each datum was compared between two plants, and the effect of soil moisture stress on stomatal opening and rate of transpiration are indicated in fig. 3. In the developing process of water stress, the stomatal opening began to decrease at pF 2.7, but the rate of transpiration began to decrease at about pF 3.4. Therefore, it was made clear that the stomatal function is more sensitive to the water shortage. 2. When water stress increased to pF 4.0, the distinct closing of stomata accompanied by transpiration depression was perceived even in the dark (fig. 3). Such a small change of aperture of stomata was easily detected by the recording porometer method but not by the infiltration method. 3. There exists a curvilinear relationship between stomatal opening and transpiration rate in the light, but it was obscure in the dark (fig. 4). A marked difference in these two curves of transpiration is caused by the existence or absence of illumination. The curve in the light indicates that the smaller the aperture operates the higher the degree of stomatal control of transpiration is. At the time when the plant is wilted and its stomatal aperture is small, actual transpiration rate shows a large depression as compared with Bange (1953)'s theoretical curve obtained by leaf disk method. Such depression may be caused by the reduction of leaf area and the change of leaf form in intact plant. The transpiration rates of recovery processes after rewatering (in dotted lines) are evidently lower than those before wilting both in the light and in the dark. 4. After rewatering, the wilted tobacco plant quickly regained its normal turgesence in external appearance. However, the recovery of full stomatal function required four days and transpiration rate did not recover enough during four days owing to the after-effect of severe wilting.

[学科分类] 农业科学（综合）