Vol. 75 No: 3

Title:
Effects of light and nitrogen supply on the allocation of dry matter and calcium in poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch)

Authors:
KIRSTEN RASMUSSEN STARKEY and NIELS ERIK ANDERSSON

pp: 251-258

Abstract:
Two poinsettia cultivars were grown under short-day conditions with three levels of supplementary light and four levels of N and the effect on growth and Ca uptake and distribution examined. Light had more influence on dry- weight production than N. The proportion of bract dry weight increased with increasing light and the proportion of leaf dry weight increased with increasing N. Increasing N reduced the root:shoot ratio and stem dry weight. Plants grown with more light had a higher percentage dry matter in all parts, whereas the strongest effect of N was on the stem, where the dry-matter percentage was significantly reduced with increasing N. Concentration and content of N in the plant increased with increasing N supply. Total content of Ca in the shoot of the plant increased with increasing N and light, and correlated well with the increase in dry weight. Ca concentration was lowest in the bracts and, within the bract, most so towards the edges. Light increased the production of dry matter and the uptake of Ca to the same extent resulting in the same concentration of Ca in all light treatments. However, the concentration and total content of Ca in the bracts decreased with increasing N supply, indicating that transport of Ca to the bracts decreased with increasing N. The concentration of Ca in the stem was lowest at lowest N and at highest light, while content was the same for all treatments, indicating a "dilution" effect of Ca in the dry matter.

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