Effect of Carbon Dioxide Concentration on Growth and Dry Matter Production of Crop Plants : 1. Effects on leaf area, dry matter, tillering, dry matter distribution ratio, and transpiration

Abstract

Crop plants at the 5 to 7-leaf stages possessing C₃ (barley, rice, and soybean) and C₄ (barnyard millet and maize) pathways of photosynthesis were cultured for 15 days in transparent growth chambers placed outdoors under 4 different carbon dioxide (CO₂) concentrations from 1/2 to 10 times the normal atmosphere (ca. 350 ppm) to make clear the effects of various CO₂ concentrations on growth and dry matter production. The following results were obtained: I. Increases in plant height and leaf area were promoted by high CO₂ concentrations, but the degree of promotion was relatively small. At a low concentration (160 ppm), plants often elongated and had narrow drooping leaves as compared to control plants under normal CO₃ concentration. 2. Increase in dry weight was promoted by high CO₂ concentrations and suppressed by a low concentration. This increase proceeded up to about 3 times (sometimes 10 times) the normal concentration, and this was effected mainly through the increase in net assimilation rate. The C₃- and C₄-plants responded differently to CO₂ concentrations, the latter giving less suppression at a low concentration and less promotion at high concentrations than the former. 3. Tillering in barley and rice was accelerated by high CO₂ concentratoins and withheld by a low concentration. In rice plants, observed at the 7-leaf stage, the promotion of tillering took place at the 4th node, and the appearance of tillers was made steadier at the 2nd and 3rd nodes by high CO₂ concentrations. 4. Distribution ratio of dry matter in rice and maize was in a marked contrast. In rice plant distribution to leaves was less and that to roots was increased at high CO₂ concentrations, while in maize such a tendency was not observed at all. 5. Transpiration rates (dm^-2 day^-1) were smaller at higher CO₂ concentrations. At a low concentration, the promotion of transpiration was enhanced day by day as the treatment proceeded. On fine days, the leaf temperature was about 1°C lower at a low CO₂ concentration and about 1°C higher at higher concentrations as compared to control plot, but no difference was observed on cloudy days.