Long-term effects of an increased CO₂ concentration on terrestrial plants in model ecosystems. Morphology and reproduction ofTrifolium repens L.and Lolium perenne L.

Abstract

Mixtures (ratio 1∶1, 45 seeds·dm⁻²) of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) were enclosed in environmentally controlled acrylic mini-glasshouses and supplied with additional CO₂ from September 1981 until September 1982 (547–600 ppm, control: ∼340 ppm CO₂). At growth optimum the single leaf area of white clover was 30% greater and the specific leaf weight 19% higher with additional CO₂; with the perennial ryegrass it was 18% resp. 29%. The length growth of the white clover petioles was enhanced by the additional CO₂: in the beginning 67% longer leafstalks, at growth optimum no effect and at the end of the experiment 100%. At growth optimum the specific petiole weight was approximately 52% higher. When the growing was terminated the blades of perennial ryegrass were 19% longer at high CO₂. The average volume of the flowerheads was about 53% greater and the adult ears 13% longer. The number of flowers per flower head and the number of earlets per ear did not increase significantly. On an average the white clover seeds were 28% heavier and the caryopses were 4% lighter.