Changes in Nitrogen Partitioning to Inflorescence and Pseudobulbs during Various Growth Stages of Oncidium 'Gower Ramsey'

Oncidium (Oncidium spp.) is an import horticultural crop for both potted plant and cut flower production. A part of its stem becomes enlarged to form a pseudobulb, which serves as a storage organ for reserve nutrients and water. As a sympodial orchid, Oncidium extends its growth by producing one or more new shoots from the base of the current shoot. These characteristics make it difficult to study the nutrient requirement of Oncidium compared with monopodial orchids. In this study, we used the stable isotope nitrogen-15 (¹⁵N) as a tracer to investigate how fertilizer nitrogen (N) is partitioned to pseudobulbs and inflorescence in the various growth stages of Oncidium 'Gower Ramsey'. Results indicated that the fertilizer N supplied during the vegetative stage in the current generation was mostly stored in the pseudobulbs, and the fertilizer N supplied during the reproductive stage in the current generation was largely allocated to the inflorescence. During a single shoot growth cycle, the later was the application of ¹⁵N-labeled fertilizer, the less was the ¹⁵N detected in the pseudobulbs while the inflorescence by contrast received more ¹⁵N. During the next generation, the source of N for the development of new pseudobulb and inflorescence came partly from the fertilizer N applied during the previous reproductive stage. Therefore, it is important to continue the supply of N during the reproductive stage of Oncidium 'Gower Ramsey' to improve the quality of cut flower produced and the shoot development of the next generation.