Phalaenopsis is among the world’s most important horticulture crops grown as flowering potted plants and is also grown for cut flower production. In recent years, Phalaenopsis is the highest grossing potted flowering plant in the world’s major floriculture markets (FloraHolland, 2013; U.S. Department of Agriculture, 2013). In addition to a long blooming period (Chang et al., 2013), Phalaenopsis is also noted for resilience against stresses (Hou et al., 2010; Hung, 2012; Lei, 2007), which makes it very versatile and adaptable, both during production and post-harvest.
Nitrogen is an important macronutrient in plants. The growth and flowering of Phalaenopsis are significantly affected by the N status in the plants (Lei, 2007; Yu, 2012). In Phalaenopsis, symptoms of N deficiency include reduced leaf number and leaf area, low chlorophyll content and reduced dry weight of leaves, and a greater incidence of leaf drop (Yoneda et al., 1997). N deficiency could also result in reduced flowering quality in Phalaenopsis (Peng, 2008; Wang, 2000; Wang and Gregg, 1994).
Although the effects of N deficiency in Phalaenopsis are known and have been reported, Phalaenopsis plants do show great resilience to N deficiency (Lei, 2007; Yu, 2012). Healthy plants can continue to grow and flower normally for a long time even under suboptimal N supply (Lei, 2007). In our previous study, we showed that this resilience to N deficiency is attributable to significant amounts of N being stored in the plants (Susilo et al., 2013). In another study, we quantified the contribution of fertilizer N stored throughout the vegetative stage of Phalaenopsis to the developing inflorescence when fertilizer supply was ample during forcing (Susilo et al., 2014). We hypothesize that reducing fertilizer level during the forcing period would increase the contribution of previously stored N to inflorescence development. To our knowledge there is no conclusive evidence to support this hypothesis in the current literature.
High rates of N before harvest are known to reduce the quality of some flowering crops (e.g., ter Hell and Hendriks, 1995). Consequently, some Phalaenopsis growers reduce or withhold fertilization altogether during the finishing stage of Phalaenopsis. Moreover, post-sale plants are often subjected to periods of no fertilization. Although effects and symptoms of N deficiency in Phalaenopsis have been reported in the literature (Lei, 2007; Peng, 2008; Wang and Gregg, 1994; Yoneda et al., 1997; Yu, 2012), how the stored N and currently applied fertilizer N are used in Phalaenopsis grown with reduced fertilizer level is still largely unknown. In the present study, we used 15N labeling to trace the use of stored N and newly absorbed fertilizer N under various fertilizer levels during the reproductive stage of Phalaenopsis.
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