An Approach to the Measurement of Photosynthetic Rate in Single Leaves by the Aeration Method : I. The effects of aeration speed, gradient of CO2-concentration and propeller drive on the photosynthetic rate of mulberry leaf

[摘要] Using an aeration chamber devised to measure the photosynthetic rate of a single leaf, the photosynthetic rate was measured by varying aeration speed, frequency of propeller rotation and gradient of CO2-concentration. The results were summerized as follows: Relation between the rotation frequency of a propeller (S), expressed by rpm and relative photosynthetic rate (Y0) expressed by the percentage of the muximum rate per leaf was empirically shown as the equation I. Y=S/(0.8231+0.0317S)+66.12 ……(Equation I) According to the equation, the relative photosynthetic rate gradually increases with the increase in rotation frequency of a propeller and reaches almost a constant value at approximately 250 rpm (fig. 2). With or without propeller drive, the relative photosynthetic rate (as expressed by percentage of the photosynthetic rate estimate under CO2gradient ranging from 8 to 12 ppm with a propeller drive than without it (Figs. 3 and 4). In the case of propeller drive (above 250 rpm), the relative photosynthetic rate was inversely proportional to CO2-gradient. In other words the relative photosynthetic rate was directry proportional to CO2-concentration in the chamber (Fig. 6). Without propeller drive, however, the relation between the relative photosynthetic rate and CO2-gradient was not linear as shown in fig. 5. The relation between CO2-gradient (Z, as expressed in ppm) and the relative photosynthetic rate (Y1) was expressed by the following equation, in the case of propeller drive (Fig. 7). Y1=102.7090-0.2424Z ……(Equation II) Measured photosynthetic rate were extrapolated to CO2-gradient of 0 ppm using the above equation and then relative photosynthetic rate were calcurated for each leaf. This modified relative photosynthetic rate (Y2) was not influenced by the aeration speed when the propeller was driven (Fig. 9). Whereas the modified relative photosynthetic rate was influenced by the volume of air supplied to the chamber (X, as expressed 1/min.) when the propeller was not driven. This relation was shown in the following equations (Fig. 8). Y2=42.4854X0.1412 ……in Aug. sample Y2=51.0313X0.1841 ……in Aug. sample ……(Equations III and IV) The equations express that modified relative photosynthetic rate increases with the increase of aeration speed in both seasens. The reason why the modified relative photosynthetic rate with the propeller drive differed from that without drive may be due to the unequal distribution of CO2-concentration in the chamber and the resultant surpression of photosynthetic rate by CO2-diffusion resistance in the chamber.

[学科分类] 农业科学（综合）