The Effects of Light Intensity and Carbon Dioxide Concentration on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne

Abstract

Rooted cuttings were grown in controlled-environment cabinets at daily visible light totals of 31, 63, 125, and 250 J cm −2 8-h day −1 and carbon dioxide concentrations of 325 and 600 ppm. The experiment was repeated on another occasion with the inclusion of a further carbon dioxide level of 900 ppm. A 5-h tungsten night break was used in the first week to delay flower initiation The plants in the various treatment combinations were sampled by frequent small harvests for leaf area and fresh and dry weights of leaf, stem, root, and flower, and also for various morphological features. Other growth measures were obtained by manipulation of the primary data, including the fitting of progress curves. Plants were respaced at intervals to minimize mutual shading. There was an increase in total dry-matter production with increasing light and carbon dioxide, with a small positive interaction between them. Plants in one experiment had a somewhat higher unit leaf rate and a lower leaf-area ratio, the latter being due to a slightly smaller leaf-weight ratio. The effects of additional carbon dioxide were largely accounted for by increased photosynthesis. Although there were substantial differences in specific leaf area between treatment combinations within each experiment, the leaf-weight ratio was little altered in the period of vegetative growth. The inverse relationship between specific leaf area and unit leaf rate showed a very similar trend for all combinations of light and carbon dioxide concentration. Leaf area was a linear function of absolute leaf water content for all treatment combinations within an experiment, but there was a small significant difference between occasions. Flower development was extremely delayed in the lowest light level and substantially delayed at the next higher level. The number of leaves below the flower decreased with increasing light level Flower weight increased with increasing light above 63 J cm −2 8-h day −1 and with increasing carbon dioxide concentration, there being a positive interaction between them The initial weight and leaf area of cuttings differed for the two experiments, and although the results on the two occasions were in the same direction, their magnitudes were different. Some of the discrepancy was eliminated by expressing the various growth measures as functions of plant dry weight, but there was evidently a difference in the potential for growth of the two batches of cuttings. The plants which were initially smaller had a higher average unit leaf rate which, due to a higher leaf water content, was not offset by a lower leaf area ratio.