Studies on Matter Production in Pineapple Plant. II. Effects of soil moisture on the gas exchange of pineapple plants

Abstract

Using pineapple plants, a cultivar selected from the Smooth Cayenne, the effects of soil moisture on the gas exchange of the top of the plants were investigated. Soil moisture levels under which the present experiments were carried out four soil moisture constants conventionally referred to in plants except for CAM plants: They were the condition of excessive water, total readily available moisture, first wilting point, and permanent wilting point. The following results have been obtained: 1. The CO2 influx occured in dark period and the last half of light period under every soil moisture condition (Fig. 1). 2. The CO2 balance in the last half of light period, in dark period, and for a whole day reached a maximum at total readily available moisture condition of pF 2 to pF 3 (Fig. 3). 3. Pineapple plants, which belong to the CAM plant, exhibited a positive CO2 balance even under the first wilting point to permanent wilting point for other plants (Fig. 1 and 3). 4. CO2 influx in the last half of light period decreased much under soil moisture condition between first wilting point and parmanent wilting point. Decrease in CO2 balance in dark period, however, was not so large under the same soil moisture conditions. 5. The time course of water vapour exchange coefficient of the whole top of a single plant was similar to that of CO2 exchange (Fig. 2). 6. Transpiration ratio, in each phase of the CO2 exchange, that is in last half of light period, dark period, and a whole day was regulated by light intensity in light period rather than soil moisture conditions (Fig. 4). 7. It was found that the effect of soil moisture obtained in the present investigations was resulted from the regulating action of stomatal aperture. © 1981, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.