Study on the respiration of crop plants. : (I) On the measuring apparatus and some results obtained with regard to the influence of excessive moisture-content of root-surrounding medium on the respiration of shoot.

摘要

(1) Apparatus for measuring respiration. In order to measure the respiration several procedures for measuring carbon-dioxide exchange between plant and air have been employed, such as volumetric, gasometric, gravimetric and electrometric, etc. All of these methods have left much to be desired either of convenience or accuracy. Of all methods the electrometric, particularly, the electro-conductivity method, is the most advanced one as concerned with the principle and the method of measuring itself. So that we attempted to construct a convenient and acurate apparatus by employing the electroconductivity method (Fig. 1). (1) Aspirator : Using three injector tubes as pistons which may be operated by means of a motor, we can force out a constant stream of air-flow of about 5∼50 litres per hour (Fig. 2). The Amount of air-flow may be adjusted by the velocity of rotation of the motor. (2) Air-flow thus forced out goes through the carbon-dioxide free air is introduced into the respiration-chamber, in which the plants are growing. (3) Respiration-chamber : Special device is given for the shape of respiration-chamber (Fig. 3). Amount of transpiration is easily measured by weighing, and even under the condition of over-saturated soil moisture content it may be also easily measured by the use of an attachment. During the measurement, respiration-chamber is kept in the water of bath of constant temperature. (4) Measuring carbon-dioxide amount by electro-conductance of the equivalent sodium carbonate solution, conductivity of the absorbent (sodium hydroxide solution) is measured using golden electrodes before and after the carbon-dioxide absorption occurs, and the difference due to the formation of sodium carbonate caused by the carbon-dioxide absorption is represented by the indicator-needle of the ammeter. (2) Effect of excessive soil moisture on the respiration. Wheat, barley (hulled and hull-less variety), soybean and rice seedlings were grown by sand-culture with modified "Knop's solution", and as they grow to some extent, half pots of each crops were treated with the excessive supply of water to the sand-bed. The influence of excessive water condition, thus given to the root part, on the respiration rates and other physiological activity of the top part was studied. (1) Soon after the plants are treated with excessive moisture supply, respiration rate of the top part of the plants shows marked response, i. e. within at least 3 hours after treatment the respiration is reduced to about 50∼40% of that of control plant (Fig. 4). On the other hand there are the slight decreases in soybean and rice, reducing to about 80∼90% of that of control plant (Fig. 5). (2) The reduction of respiration seems to recover gradually, but after five days the effected wheat and barley still show about 50∼70% of that of control plant, and soybean about 95%. On the contrary rice seedlings show a definite increase over control plant within at least two or three days after treatment. Thus rice seedlings show the different reaction to the excessive soil moisture content as compared with the other crops. (3) It is also found that absorption of water by roots is reduced by the treatment. Not only "passive absorption" of water but also "active absorption" is inhibited by the excessive moisture condition, and as a result plants show decreased turgor pressure and also decreased water content of the body.