Effect of Carbon Dioxide Concentration on Growth and Dry Matter Production of Crop Plants : II. Specific and varietal differences in the response of dry matter production

Abstract

Seedlings of crop species possessing either C₃ or C₄ pathway of photosynthesis were cultured for 8 to 20 days under 4 different CO₂ concentrations from 1/2 to 10 times the normal atmosphere (ca. 350 ppm) in transparent growth chambers placed outdoors to reveal out the differences in the rate of dry matter production (RGR) in response to CO₂ concentration among 12 crop species, 27 varieties, or culture seasons (Tables 1 and 2). The following results were obtained: I. In the optimal growth season for each species, the promotion of RGR at higher CO₂ concentrations was greater than in a suboptimal season. When C₃ and C₄ species were cultured in the same favorable season, the response of C₃ species to CO₂ concentration was greater than C₄ species. But in a suboptimal, lower temperature season, the effect of CO₂ decreased and the difference in the response to CO₂ concentration between C₃ and C₄ specics became so small that the distinction between the two groups was difficult (Fig. 1). 2. Varietal differences in the response to CO₂ concentration of 7 crops were investigated. Although the level of RGR differed greatly among varieties, the pattern of response to CO₂ concentration was roughly equal in all varieties examined (Fig. 2). 3. High positive correlations were obtained between the RGR under the normal CO₂ (350 ppm) and that under other concentrations, indicating that the plant possessing a higher RGR under normal CO₂ also had a higher RGR under other concentrations, but that the degree of promotion under higher CO₂ concentrations (3 to 10 times) roughly remained constant irrespective of the levels of RGR in normal CO₂. From these observations it may be concluded that the pattern of crop varieties in their response of RGR to CO₂ concentration is quite similar irrespective of culture seasons (Fig. 3).