Effect of Carbon Dioxide Concentration on Growth and Dry Matter Production of Crop Plants : IV. After-effects of carbon dioxide-treatments on the apparent photosynthesis, dark respiration and dry matter production

Abstract

Two kinds of experiments were carried out to confirm after-effects of CO₂-treatments on the apparent photosynthesis, dark respiration and dry matter production of crop plants kept under normal CO₂ concentration. The following results were obtained: 1. Five crop species possessing C₈- and C₄-photosynthesis characteristics were cultured in plastic growth chambers placed outdoors for 7 to 15 days under 4 different CO₂ concentrations (160 to 3200 ppm), natural light and temperature in optimal growth seasons for each species. Apparent photosynthesis and respiratory activities of these plants were determined in the same ambient air (ca. 350 ppm). In 6-rowed barley, rice and soybean (C₃-species), the after-effects of CO₂-treatments were observed to exist. Low CO₂ (160 ppm)-treated plants exhibited higher photosynthetic activity, and high CO₂ ( 1000, 3200 ppm)-treated plants exhibited lower photosynthetic activity than those kept under normal CO₂ (350 ppm). Dark respiration was somewhat enhanced by high CO₂-treatments, but the degree was too small to cause the reduction in the apparent photosynthetic rate. In Japanese millet and maize (C₄-species), the after-effects of CO₂-treatments were scarcely observed to exist (Table 1, Fig. 2). 2. A 9 days' CO₂-treatment of rice and Japanese millet was conducted in the same way as described above. At the end of treatment, plants were transferred to a glasshouse and their subsequent growth was analyzed by use of the growth analysis method (Fig. 1). In rice, after-effects of high CO₂-treatments were clearly revealed out in RGR and NAR just after the termination of treatments, disappearing in subsequent period. RLGR was not affected so much. In Japanese millet, a C₄ species, these after-effects were comparatively small. Low CO₂-treatment somewhat promoted RGR just after the termination of treatment (Table 2, Fig. 3). 3. From these observations, it was concluded that CO₂ concentration in the atmosphere gives after-effects on photosynthetic activity of plants, with high CO₂ concentration (above 1000 ppm) decreasing the potential of photosynthesis by some factors (for example, increase in stomatal or mesophyll resistance, etc.) other than dark respiration.