Nitrogen Requirements for Vegetative Growth, Flowering, Seed
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CROP PRODUCTION HORTSCIENCE 47(5):585–588. 2012. and restrict distributions are pushing this endangered genus to the verge of extinction (Tsi et al., 1999), and it is listed as a Conven- Nitrogen Requirements for Vegetative tion on International Trade in Endangered Species of Wild Fauna and Flora Appendix I Growth, Flowering, Seed Production, species. To date, the few studies on P. arme- niacum are focusing on asymbiotic cultiva- and Ramet Growth of Paphiopedilum tion, conservation ecology, mycorrhizal fungi, molecular taxonomic identification, photosyn- thetic physiology, and morphological struc- armeniacum (Orchid) ture. However, little is known about its growth Mou Zong-min, Yan Ning, Li Shu-yun, and Hu Hong1,2 and reproduction after deflasking (transplan- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of tation of seedlings from culture vessels to pots). The study of nutrient physiology can- Botany, Chinese Academy of Sciences, Kunming 650204, China not only facilitate cultivation in horticulture, Additional index words. nitrogen availability, leaf traits, sexual reproduction, clonal reproduction, but could be helpful in conservation ecology slipper orchid of this endangered species. The aims of this study were to evaluate Abstract. Paphiopedilum armeniacum S. C. Chen et F. Y. Liu is endemic to China and has the effects of N on the vegetative growth great ornamental value. Little is known about its nutrient requirement for growth and and reproduction of P. armeniacum to find reproduction after deflasking (transplantation of seedlings from culture vessels to pots). the appropriate N level for cultivation and We studied the effects of adding nitrogen (N) (0, 105, 210, and 420 mgÁL–1) on the vegetative production. growth and reproduction of P. armeniacum. N enrichment improved leaf area and lengthened the leaf lifespan during the vegetative stage. The effects of N application on Materials and Methods flower size were minor. The intermediate N level of 210 mgÁL–1 (MN) increased the seed capsule weight, seed germination rate, and improved the growth of seedlings that Growth conditions and treatment. This developed from seeds of MN-treated plants. N fertilizer exerted little influence on ramet study was performed in Kunming, Yunnan, emergence and ramet number per plant, but a low N concentration of 105 mgÁL–1 China. In Nov. 2008, 200 5-year-old mature promoted the leaf number and leaf area of ramets. Appropriate N levels for P. armeniacum plants with visible flower buds and 360 3-year- in production and cultivation should be determined according to different production old seedlings were randomly selected and trans- objectives. planted into 0.785-L plastic pots (0.1 m wide and 0.1 m deep) filled with sphagnum moss, which is commonly used as potting material Nitrogen is one of the major structural hybrid (Bichsel et al., 2008). Kubota et al. for orchids. All the materials were germinated elements of organisms and it plays an impor- (2009) observed that N application increased from seeds by asymbiotic propagation (for 1 tant role in plant growth and reproduction. biomass and leaf area of the current shoot in year) and grown in a greenhouse potting bark. However, N deficiency is widespread in many Odontioda and also increased the number of Plants had four to six leaves and no ramets. ecosystems. An insufficient N supply reduces florets. The optimal amount of N application These plants were divided into four groups, plant growth and leaf area and induces a de- was 560 mg/pot/year in the experiment. In- respectively, by a completely random design crease in the rate of photosynthesis and leaf N creasing the N fertilizer from 50 to 200 mgÁL–1 and then tagged with numbered tags. All plants content (Boussadia et al., 2010; Chapin et al., increases flower count, flower number, stalk were maintained in the greenhouse under a 1988; Ferrar and Osmond, 1986; Munoz et al., diameter and length, and leaf growth in a Pha- natural light source, at a controlled temperature 2005; Paul and Driscoll, 1997). Changing the laenopsis hybrid (Wang and Gregg, 1994). (24/18 °C, day/night), and watered as needed. N supplementation, sources, and applying its Lower N caused thinner bulb diameter and Two weeks later, the plants of the four groups isotopes to plants are the commonly used flower stalks, fewer roots and flowers, and were grown at one of four N levels: 0N (0 methods of plant nutrient physiology to esti- advances in flowering date in Odontoglossum mgÁL–1), LN (105 mgÁL–1), MN (210 mgÁL–1), mate biomass partition, reproductive allocation, hybrid (Yoneda et al., 1999). Generally, the and HN (420 mgÁL–1). The N levels were and its roles in other physiological processes. optimal applications of N vary among orchid generated by applying 50 mL Hoagland’s The management of N is widely used in hor- species. When quantity of N surpasses a level, solution (Hoagland and Arnon, 1950) with no ticultural plants to optimize plant physiolog- growth and flowering will be inhibited rather N, 50% N, 100% N, and 200% N at the begin- ical characteristics, e.g., high-quality flowers than promoted (Duan and Yazawa, 1995; ning of each month from Nov. 2008 to Aug. and vigorous seeds, which are valuable in Wang, 2003). 2009. CaCl2 and KCl were used to balance horticulture and seedling production, respec- Paphiopedilum armeniacum is endemic potassium and calcium in all solutions. Plants tively. For ornamental orchids, N fertilization to China and is well known as slipper orchid. were watered when the moss surface became can help growers produce orchids more effi- It is famous for its golden yellow flowers and dry. ciently. The addition of N increases the number long flowering period. First class certificates Measurements. In Mar. and Apr. 2009, the of leaves and flowers in Dendrobium nobile have been awarded to P. armeniacum by the length of the flowering period, labellum di- and 100 mgÁL–1 N is recommended for this American Orchid Society, Royal Horticul- ameter, dorsal sepal diameter, petal diameter, tural Society, and many others (Cribb, 1998). and peduncle length were recorded for each P. armeniacum is a hemiepiphyte on karst mature plant during the flowering phase. All limestone cliffs and slopes in shady forests at the diameters were measured from the point Received for publication 11 Jan. 2012. Accepted elevations of 1400–2050 m in west Yunnan of attachment to the top using a slide caliper. for publication 19 Mar. 2012. of China. The limestone area is characteristic Hand pollination was performed on the fifth Research supported by the Western Light Foun- of scarcity of soils and nutrient deficiency, day after bloom for 25 plants per treatment dation of The Chinese Academy of Sciences and especially in N and phosphorus (P). Mean- group. The emergence and number of ramets Yunnan Social Development Science Program while, vascular epiphytes are always limited and their sizes (leaf area and leaf number) in the (No. 2007C0001Z, 2009CD116). We thank Seng-yin Liu and Jia-lin Huang for their by low nutrient availability in situ and point mature plants were determined on Sept. 2009. kind help. to N and/or P limitations (Zotz, 2004; Zotz The seed capsule weight was measured at 1Professor. and Asshoff, 2010). In general, the habitat of 60, 90, and 120 d after pollination (DAP). The 2To whom reprint requests should be addressed; P. armeniacum is nutrient-poor. In the past 120 DAP seed capsule was surface-sterilized e-mail [email protected]. decades, habitat destruction, overcollection, and the seeds were scattered on the surface of HORTSCIENCE VOL. 47(5) MAY 2012 585 1/4 Murashige and Skoog (MS) basal medium one-way analysis of variance. Ramet emer- as shown in Figure 1D. Although juvenile (Murashige and Skoog, 1962) supplemented gence rates were tested by chi-square test. plants fertilized with HN had fewer new leaves with 30 gÁL–1 potato mash and (mgÁL–1): Significant differences between N rates were and withered leaves, the leaves were larger activated carbon (300), sucrose (20,000), agar determined with linear contrasts. Differences with HN compared with 0N. (8,000), and kinetin (0.25). The seed germi- were considered statistically significant at a In juvenile plants, the 0N and LN (105 nation rates were calculated after 90 d incuba- probability of P # 0.05 in all tests. Graphs mgÁL–1) treatments had the lowest leaf N tion of seeds in a dark room at 25 ± 1 °C. The were plotted with SigmaPlot 10.0 (Systat, San concentrations in both the new and old leaves germinated protocorms were transferred on Jose, CA). (Table 1). Chl a/b was not different between 1/2 MS medium with the previously listed N rates, whereas the effect of N rate on Chl supplements and cultured under a fluorescent Results a+b was quite similar to those for the leaf N lamp source at a photosynthetic photon flux concentrations. There was almost a threefold density of 40 mmol photons/m2/s with a pho- Influence of nitrogen on vegetative growth. increase in Chl a+b when N rate increased toperiod of 12:12 (light: dark) at a controlled In juvenile plants, N rate did not affect total from LN to MN. No variations were detected temperature (24/18 °C, day/night). After 6 leaf number during the experiment (Fig. 1A). in Chl a/b among treatments. 0N plants had –1 months cultivation, 48 seedlings of each The HN (420 mgÁL ) plants produced fewer the lowest Fv/Fm of 0.61, whereas Fv/Fm was treatment were sampled. The N concentra- new leaves and withered leaves than other 0.83 to 0.85 in the plants receiving N. tion, carbon (C) concentration, leaf num- treatments as shown in Figures 1B and 1C.