The Uptake and Partitioning of Nitrogen In Phalaenopsis Sogo Yukidian

The low growth rate and slow response to fertilizer application of Phalaenopsis make it difficult to understand its nutrient requirement. In this study, we used stable nitrogen isotope, ¹⁵N, to trace nitrogen absorption and partitioning in Phalaenopsis. Mature Phalaenopsis Sogo Yukidian ‘V3’ plants were potted in sphagnum moss and fertigated with modified Johnson’s solution. The KNO₃ in the solution was partially substituted by K¹⁵NO₃. Both roots and leaves were capable of taking up nitrogen; the uptake efficiency was highest in new roots, lower in old roots, and lowest in leaves. There was no difference on nitrogen uptake efficiency between upper and lower leaf surfaces. After one single ¹⁵N application, tissue ¹⁵N content reached a plateau about 8 weeks after treatment. These results indicated that sphagnum moss is a substrate good for retaining fertilizer and Phalaenopsis has a high efficiency for nutrient utilization. Growing young leaf is the major sink during vegetative growth stage and stalk during reproductive phase. The sink strength of leaves decreased as the leaf age increased. Data revealed that mature leaves and roots act as storage organs and are able to translocate nitrogen to stalks during reproductive phase; this explains why well-grown Phalaenopsis can still flower after months of fertilizer cessation.