水稲収量予察の作物学的研究 (予報) XII, XIII, XV : 戸外の全植物体を対象とした水稲の炭素同化作用

抄録

(1) Since the yields of cereal crops can be said to be the products of their Carbon assimilation, it is very important, as fundamental data for increasing or forecasting their yields, to trace up their responses of the rate of assimilation to the various external conditions in different growing stages. Many former photosynthetic experiments were carried out on detached leaves or in-natural conditions, while the authors tried to measure the rate of corbon assimilation, using whole plant, under as nearly natural conditions as possible with the purpose of applying the results to cultural practices and yield-forecasts of crops. (2) Refering to the method of THOMAS and HILL (1937, '50), the authors constructed a apparetus to measure the rate of carbon assimilation. The apparatus consists of 4 sets. 0ne set of them is shown in Fig. 1. A blower (A) pumps out air stream with constant flow into a cooler (B). Being measured by oriffice (C) and manometer (J), the flow of the air can be adjusted by the blower from 30 litres to 150 litres per minute, in proportion to the rate of carbon assimilation, not to reduce the concentration of carbon-dioxide lower than 80 percent of the normal one. The size of plant-chamber is 50cm. square and 50cm. high for seedling plants and 50cm. square and 100cm. high for adult plants. The most part of the air stream going into the plant-chamber is sent out from a out-let (F), but a part of it is sucked out by a pump (M) as an air sample. The sampled air is pumped out again by the pump (M) into a absorber (O) placed in a waterbath (P) of constant temperature (30 ± 0.02°C) at the velocity of about 300 ml./min. The absorbing solution is 0.005 N sodium hydroxide, containing 1 percent butyl alcohol. A sintered glass dish fixed in the bottom of the absorber breaks up the air stream into very fine bubbles, the alcohol causes foaming and thus prolongs the period of contact between the bubbles and the liqued. The progress of the absorption is determined by measuring the electrical conductivity of the solution with impedance bridge (1000 cycle/sec.), as it changes from hydroxide to carbonate. From the calibration curves between electrical conductivity and the solution differing in the ratio of content of sodium hydroxide and sodium carbonate the amount of the absorbed carbon-dioxide can be easily read at the accuracy of 0.01 mg. Basing upon the difference of the amount of absorbed carbon-dioxide between blanck set and assimilation set, the rate of photosynthesis (apparent assimilation) can be easily calculated. (I....Solarimeter, H.....Thermocup, G.....Small cooler, Q.....Platinum electrode, U.....Gas-meter) Using the present apparatas, the authors made some experiments with rice plants. Results obtained are summarized as follows. (3) Relation between the rate of carbon assimilation and light intensity. From the results of measurements, using 3 varieties and controlling the sunlight with white clothes and natural clouds, in their various growing stages from seedling stage until ripening, it was made clear that the rate of carbon assimilation increases with light intensity up to about 0.5 cal./cm².min., but it does not almost increase in greater intensities than 0.6 cal./cm².min. throughout their growing periods, except the later period than about 17 days after heading. In other words, so-called "light curve" of rice plant resembles closely with Blackman's curve, and its light saturation point seems to be about 0.6 cal./cm².min., except in late stage. In later stages than 17 days after heading both the rate of photosynthesis and the light intensity of saturation seemed to begin to fall off day by day. (Fig. 2 and 3) (4) Diurnal changes of the rate of carbon assimilation. For the experiments in cloudless days, using Norin-No. 25 and No. [the rest omitted]