Hong Kong orchid tree is an outstanding flowering tree for tropical and subtropical regions of the world (Barwick, 2004). It is a hybrid between Bauhinia purpurea L. and Bauhinia variegata L. and, unlike its parents, does not set fruit and, thus, is not weedy. It has an extended flowering period, which in south Florida lasts from early November through January. Although these trees have attractive green foliage during the summer months, by October older leaves on each shoot typically develop moderate to severe K, Mg or both deficiency symptoms on south Florida’s sandy, nutrient-poor soils. These deficiencies are not only unsightly, but also cause premature senescence of the older leaves, leading to complete defoliation by April. Thus, these deficiency symptoms detract from the esthetic appearance of these trees during their showiest season. Potassium deficiency symptoms appear as an extensive interveinal and marginal necrosis of the oldest leaves, whereas Mg deficiency symptoms appear as an interveinal chlorosis of these same-aged leaves (Broschat, 2008; Dickey, 1983). Some trees display deficiency symptoms of both elements simultaneously, but typically only one element is deficient on a particular tree at any point in time.
Because the terminal inflorescences of Hong Kong orchid tree produce about a dozen large flowers over the course of 3 months, it is suspected that the flowers are acting as a sink for mobile nutrient elements resorbed from older leaves on the same shoot. There are few published data relating nutrient mobilization from leaves to flowers in woody plants, although the mobilization of nutrients from leaves to stems and developing fruits is well documented (Hill, 1980; Tagliavini et al., 2000; Williams, 1955). As individual flowers within an inflorescence of Hong Kong orchid tree open sequentially, perhaps even senescing flowers provide nutrients for redistribution to younger flowers. Trivellini et al. (2011) demonstrated that senescing flowers of Hibiscus rosa-sinensis L. contain notably less N, P, K, and Mg than open flowers, suggesting remobilization of these elements.
Because most nutrient deficiencies can be prevented or treated with appropriate fertilizers, it would be useful to determine if the K and Mg deficiencies that plague Hong Kong orchid trees during the fall, winter, and spring months could be prevented. The objectives of this study were 1) to determine the seasonality of these nutrient deficiencies and their relationship to flowering and new leaf growth and 2) to determine how fertilization affects the growth, flowering, and development of K and Mg deficiencies in Hong Kong orchid trees growing in south Florida.
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