Phalaenopsis is currently the most important pot flower in market value in the world’s major floriculture markets (FloraHolland, 2013; U.S. Department of Agriculture, 2013). One characteristic of Phalaenopsis orchids is the long vegetative period before the plants are ready to be forced into marketable flowering plants (Runkle et al., 2005). Flowering in Phalaenopsis orchids is easily achieved by low temperature and conversely inhibited by high temperature (Lee and Lin, 1984).
Sphagnum moss is a popular potting substrate in the commercial production of Phalaenopsis. In this substrate, greenhouse-grown standard-type Phalaenopsis plants in Taiwan and plants grown elsewhere using the Taiwanese method generally undergo three stages during the vegetative stage and are potted-up twice: from 4.5- to 8.5-cm pots, and finally to 10.5-cm pots, in which plants are grown until flowering. In this study, we refer to the respective three vegetative stages as Stage I (small plant in 4.5-cm pot for 5 months), Stage II (medium plant in 8.5-cm pot, 5 months), and Stage III (large plant in 10.5-cm pot, 5 months).
Nitrogen is an important macronutrient that significantly affects the growth and flowering of Phalaenopsis (Lei, 2007; Yu, 2012), whereas N needs during flowering are of particular interest. To our knowledge, the relative contributions of stored N and recently absorbed fertilizer N to the developing inflorescence have not been studied in Phalaenopsis. The relative contributions to the stored N pool of N accumulated during the different growth stages during the long vegetative period of Phalaenopsis cultivation were also unknown. The objective of this study is to bring answers to these unknowns.
15N-labeling is a powerful research tool for accurately determining the fate of N in the environment (Hauck and Bremner, 1976). The nutritional study of Phalaenopsis is difficult with traditional methods because it has a strong buffering capacity against nutrient deficiency, but we have used 15N-labeling with the enrichment method to accurately trace the absorption and partitioning of fertilizer N in Phalaenopsis (Susilo et al., 2013). In this study, we used 15N-labeling to compare the contributions of fertilizer N, applied before or after spiking, to the developing inflorescence and compare the relative contributions of fertilizer N absorbed during various stages of the vegetative period to the stored N pool.
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