EFFECTS OF CARBON DIOXIDE CONCENTRATION ON GROWTH OF CALLISTEPHUS CHINENSIS CULTIVAR JOHANNISTAG

Carbon dioxide enrichment to 600 ppm increased the amount of dry matter produced by Callistephus chinensis plants in growth cabinets with negligible mutual shading over a period of 18 weeks. Further enrichment to 900 ppm showed smaller and more variable increases. These effects were the result of a higher unit leaf rate of the treated plants. The direct effect on unit leaf rate was partly offset by a reduction in leaf-area ratio, and this was due almost entirely to the effect on specific leaf area with hardly any effect on leaf-weight ratio. Carbon dioxide accelerated flower development by about a week at 600 ppm and somewhat less at 900 ppm. The proportion of the total plant weight in the form of flowers showed a similar trend with time in all treatments and the relationship between flower-weight ratio and dry-matter content of flowers was likewise similar for all treatments, with the highest dry-matter contents of about 19 per cent associated with the highest flower-weight ratios of about 0.44 for mature flowers. Carbon dioxide enrichment significantly increased the dry-matter content of leaves. The efficiency of energy conversion based on incident light and a twenty-four-hour cycle of 8 h light and 16 h dark for small plants of 140-300 mg total dry weight (leaf areas of 50-120 cm2) was about 4.7 per cent for the 325 ppm treatment, 6.3 per cent for 600 ppm, and 5.5 per cent for 900 ppm. By reference to some further experiments on the growth of C. chinensis cultivar Johannistag in glasshouse conditions, considerable adaptive response to high and low light intensity was also demonstrated. © 1969 OXFORD UNIVERSITY PRESS.