Nitrogen Source for Inflorescence Development in Phalaenopsis: I

J. AMER.SOC.HORT.SCI. 139(1):69–75. 2014. Nitrogen Source for Inflorescence Development in Phalaenopsis: I. Relative Significance of Stored and Newly Absorbed Nitrogen Hadi Susilo, Ying-Chun Peng, and Yao-Chien Alex Chang1 Department of Horticulture and Landscape Architecture, National Taiwan University, 1 Roosevelt Road Sec. 4, Taipei 10617, Taiwan ADDITIONAL INDEX WORDS. moth orchid, nitrogen-15, nitrogen partitioning, nutrient mobilization, sink-source relationship, stable isotope ABSTRACT. Phalaenopsis orchid is a slow-growing crop that responds slowly to fertilization. In this study, we used 15N- labeled Johnson’s solution to investigate the accumulation and use of fertilizer nitrogen (N) during the vegetative and reproductive growth stages of Phalaenopsis Sogo Yukidian ‘V3’ with a focus on the nitrogen source for inflorescence development. Labeling of fertilizer applied to mature plants 6 weeks before forcing or at 6 weeks into forcing showed that in the inflorescence, the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 31% to 69%, which shows the importance of newly absorbed fertilizer for supplying the N needed for inflorescence development. The fate of fertilizer N applied during the small, medium, or large plant stage of vegetative Phalaenopsis Sogo Yukidian ‘V3’ was traced separately with 15N-labeling. The capacity of the plant to accumulate N after fertilizer application was different during the various stages of vegetative growth, with large plants having more N storage capacity as a result of their greater biomass. However, the percentage of the accumulated N that was later allocated to the inflorescence was similar regardless of the stage of fertilizer application: of the fertilizer N absorbed during various stages of the vegetative period, 6% to 8% was allocated to the inflorescence at the visible bud stage. This result highlights the mobility of N stored early on within the plant. By calculation, of the total N in the inflorescence at the visible bud stage, the N absorbed during the small, medium, and large plant stages contributed 7%, 11%, and 25%, respectively, whereas N applied after spiking made up the other 57%. This result indicates that both N stored during the vegetative stage and N applied during the reproductive stage contribute significantly to inflorescence development. Phalaenopsis is currently the most important pot flower Nitrogen is an important macronutrient that significantly in market value in the world’s major floriculture markets affects the growth and flowering of Phalaenopsis (Lei, 2007; (FloraHolland, 2013; U.S. Department of Agriculture, 2013). Yu, 2012), whereas N needs during flowering are of particular One characteristic of Phalaenopsis orchids is the long vegeta- interest. To our knowledge, the relative contributions of stored tive period before the plants are ready to be forced into N and recently absorbed fertilizer N to the developing in- marketable flowering plants (Runkle et al., 2005). Flowering florescence have not been studied in Phalaenopsis. The relative in Phalaenopsis orchids is easily achieved by low temperature contributions to the stored N pool of N accumulated during the andconverselyinhibitedbyhightemperature(LeeandLin,1984). different growth stages during the long vegetative period of Sphagnum moss is a popular potting substrate in the Phalaenopsis cultivation were also unknown. The objective of commercial production of Phalaenopsis. In this substrate, this study is to bring answers to these unknowns. greenhouse-grown standard-type Phalaenopsis plants in Tai- 15N-labeling is a powerful research tool for accurately wan and plants grown elsewhere using the Taiwanese method determining the fate of N in the environment (Hauck and generally undergo three stages during the vegetative stage and Bremner, 1976). The nutritional study of Phalaenopsis is are potted-up twice: from 4.5- to 8.5-cm pots, and finally to difficult with traditional methods because it has a strong 10.5-cm pots, in which plants are grown until flowering. In this buffering capacity against nutrient deficiency, but we have study, we refer to the respective three vegetative stages as Stage used 15N-labeling with the enrichment method to accurately I (small plant in 4.5-cm pot for 5 months), Stage II (medium trace the absorption and partitioning of fertilizer N in Phalae- plant in 8.5-cm pot, 5 months), and Stage III (large plant in nopsis (Susilo et al., 2013). In this study, we used 15N-labeling 10.5-cm pot, 5 months). 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. Received for publication 19 Sept. 2013. Accepted for publication 2 Dec. 2013. This research was funded by a grant from the National Science Council, Executive Yuan, Taiwan (NSC 98-2313-B-002-014-MY3). Materials and Methods This study consists of portions of the theses submitted by Hadi Susilo and Ying- Chun Peng in partial fulfillment of their Master of Science degree requirements. EXPT.1:ABSORPTION AND PARTITIONING OF FERTILIZER N We thank Yu-Chun Chen and Yi-Ai Guo for their assistance in the early part of BEFORE AND AFTER LOW-TEMPERATURE FORCING. The objective Expt. 2. We are grateful to Ya-Chi Yu for helpful discussions in Expt. 2. We also thank the Stable Isotope Facility at the University of California, Davis for of this experiment was to determine the absorption and performing the 15N analysis. partitioning of N in Phalaenopsis plants before and after low- 1Corresponding author. E-mail: [email protected]. temperature forcing as well as the source of N being used for J. AMER.SOC.HORT.SCI. 139(1):69–75. 2014. 69 inflorescence development. Vegetatively propagated plants of that 15N-labeling was ended at the end of each of Stages I, II, the white, large-flowered Phalaenopsis Sogo Yukidian ‘V3’ in and III. 10.5-cm pots with five or six leaves were used. The experiment Plants were divided into five groups and each given one of was conducted over a period of 18 weeks. The 15N-labeling the following treatments: 1) no 15N label application (control); treatments were performed by subirrigating the plants once 2) single application of 15N 3 months into Stage I; 3) single with modified Johnson’s solution (Johnson et al., 1957) labeled application of 15N label 3 months into Stage II; 4) single with 11.25 atom% 15N at various points in time: 1) no labeling application of 15N label 3 months into Stage III; and 5) three 15N treatment (control); 2) 15N-labeling at the start of the experi- label applications, each done 3 months into Stages I, II, and III. ment (6 weeks before low-temperature forcing); 3) 15N-labeling The timing of 15N label application was designed so that in each 6 weeks after low-temperature forcing was initiated; and 4) 15N- of Stages I, II, and III, the plants had the same duration of 15N- labeling both at the start of the experiment and 6 weeks after labeling of 2 months. 15N-labeling was conducted by subirri- low-temperature forcing was initiated. There were four treat- gating the pots once with full-strength Johnson’s solution ments with six replications each. The timing of the single enriched with 22.5 atom% 15N. Seven plants from each treatment application of 15N label was designed as such, so that plants group were sampled at each of the following sampling points: 1) were exposed to 15N-enrichment for the same duration (6 first sampling: end of Stage I; 2) second sampling: end of Stage weeks) after each 15N application. In the first 6 weeks of the II; 3) third sampling: end of Stage III; 4) fourth sampling: visible experiment, the plants were grown in a phytotron at 30/25 °C bud stage; and 5) fifth sampling: stage where two-thirds of all (day/night) under natural photoperiod and maximum light flowers on the inflorescence were open. Sampled plants were intensity of 450 mmolÁm–2Ás–1 at National Taiwan University divided into their respective shoots and roots and also inflores- (Taipei, Taiwan) to maintain vegetative growth. After the 6- cences for the fourth and fifth sampling points. The plant parts week period, the roots of all plants were cleaned of the old were measured for fresh weight and dry weight and then ground substrate, washed with tap water, and the plants were repotted tofinepowderbeforetotalNand15Nanalysis. into fresh substrate to cease 15N enrichment in the substrate 15N-LABELING OF FERTILIZER. Modified Johnson’s solution surrounding the roots. The plants were then transferred to a was used as the fertilizer in all experiments. It contained 16 mM phytotron at 25/20 °C (day/night) with maximum light intensity N, 2 mM phosphorus, 6 mM potassium, 4 mM calcium, 1 mM of 450 mmolÁm–2Ás–1 for 12 weeks for forcing into the re- sulfur, 1 mM magnesium, 50 mM chlorine, 25 mM boron, 5 mM productive stage. At the time 15N-labeling was conducted in manganese, 4 mM iron, 2 mM zinc, 0.5 mM copper, 0.1 mM Treatments 3 and 4 (6 weeks into low-temperature forcing), the molybdenum, and 0.1 mM nickel with an ammonium-to-nitrate plants had spikes 5 cm long. ratio of 1:7. 15N-labeling was achieved by enrichment of the All plants were fertigated at the same time by subirrigating potassium nitrate in the Johnson’s solution with 60 atom% 15N- with Johnson’s solution when the surface of the substrate labeled potassium nitrate (ISOTEC, Miamisburg, OH). In Expt. appeared dry. Except when 15N-labeling was being performed, 1, the 15N-labeled solution had a 15N concentration of 11.25 unlabeled Johnson’s solution was used for fertigation.

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