Abstract
It has been clarified that the rates of apparent photosynthesis in C3 plant such as rice and wheat, which evolve a large quantity of carbon dioxide in the light, become higher as the oxygen concentration in the air decreases. However, the drastic change in oxygen concentration from 21 per cent to a few per cent may inhibit some of the physiological functions of plant which have adapted to the present atmosphere. The present experiment was conducted to evaluate the effect of low oxygen concentration for a long period on dry matter production and growth of rice plant. The plant was kept in the assimilation chamber in both control and low oxygen plots. The plant in low oxygen plot was treated with the air containing 3 per cent oxygen and the plant in control plot was aerated with ordinary outdoor air. The gas treatment was conducted only in the daytime for 20 days from the heading stage to the milky dough stage. The following results were obtained. 1. The increased weight of dry matter during the treated period was significantly higher in the low oxygen plot than in the control. This increase was mainly due to the reduced photorespiration rate in low oxygen concentration. 2. The space between tillers was extremely expanded after 20 hours from the begining of low oxygen treatment. 3. When the rice plant was exposed to low oxygen concentration at flowering time, remarkable sterility occurred. Such phenomenon was also observed when only the panicle was kept in low oxygen concentration. Thus, the sterility observed here seems to be caused, not by the translocated substances from the leaf and stem, but by the direct damage of low oxygen to fertilization. 4. The grain fertility of Cyperus microiria Steudel, on the other hand, was hardly affected by oxygen concentration of 3 per cent at which the rice plant showed remarkable sterility. This fact suggests that the influence of low oxygen on fertility of plant differs with species. 5. It follows from these findings that the lowering of oxygen in the air is effective in increasing the dry matter production of rice plant, while deteriorate the physiological functions relating to fertility and growth.
