大白花蝴蝶蘭'V3'對肥料氮之吸收、儲存及利用

Abstract

蝴蝶蘭為全球性的重要花卉作物。植物體內氮的運移可藉由15N標定法追蹤分析，此方法尤其適用於追蹤蝴蝶蘭對氮之吸收及運移。本研究以15N追蹤法分析肥料氮於大白花蝴蝶蘭’V3’ (Phalaenopsis Sogo Yukidian ‘V3’)之運移，並著重於蝴蝶蘭對不同型態氮吸收之偏好、新根老根吸收效率之比較、肥料氮由蝴蝶蘭根部運移至葉片之速率、肥料氮於營養生長各階段之儲存情形以及生殖生長期不同給肥量對儲存氮利用率之影響。將含有等量尿素、銨態氮及硝酸態氮的養液施用於蝴蝶蘭之地上部或地下部，並將15N分別標定在不同型態的氮上，結果顯示蝴蝶蘭根部對不同型態氮之吸收偏好以銨態氮最高，尿素次之，而對硝酸態氮之偏好最低。相反之，蝴蝶蘭葉片的吸收偏好依次為硝酸態氮、尿素、銨態氮。將經15N標定之Johnson養液施用於新根或老根，三週後分析新葉與老葉中的15N濃度與含量，得知新根對氮之吸收效率遠高於老根。將經15N標定的Johnson養液施用於蝴蝶蘭之根部，肥料氮於0.5天後便能於葉片偵測到，並於8天之試驗期間內持續累積在葉片中。但新葉所累積之氮，只有小部分來自肥料氮，大部分來自儲存氮。另一試驗分別於蝴蝶蘭小苗、中苗、大苗階段給予經15N標定的肥料氮，得知蝴蝶蘭各個苗期所吸收儲存的肥料氮，會有一定且相似的比例分配至花梗。於花苞可見階段，運移至花梗中的儲存氮分別有16%、25%及59%來自小苗、中苗及大苗期所儲存的氮。於生殖生長期若給肥量減少則儲存氮之利用率提高。因此，蝴蝶蘭栽培的各階段均應持續供應足夠的肥料以使植株累積大量養分。試驗的結果亦顯示蝴蝶蘭的成熟葉與根部均有儲存氮的功能。

Phalaenopsis is one of the most economically important floriculture crops, and its cultivation is still increasing worldwide. 15N-labeling is an accurate analytical tool for studying the fate of nitrogen in plants, and is especially useful for tracing the absorption and partitioning of nitrogen in Phalaenopsis. In the present study, 15N-labeling was used to study the fate of fertilizer-derived nitrogen in Phalaenopsis Sogo Yukidian ‘V3’, with focus on the absorption preference for various nitrogen forms, the efficiency of absorption by roots, the rate of allocation from roots to leaves, storage over the various stages of the vegetative period, and utilization of the stored nitrogen under different fertilization levels during forcing. 15N-labeling of urea-, ammonium-, or nitrate-nitrogen supplied together in equal molarities to Phalaenopsis Sogo Yukidian ‘V3’ shoot or roots revealed that in decreasing order, the order of uptake preference by roots was ammonium, urea, and nitrate, while the order of uptake preference by leaves was nitrate, urea, and ammonium. By tracing the fate of fertilizer nitrogen in young and mature leaves 3 weeks after application of 15N-labeled Johnson’s solution to the young or old roots, much higher nitrogen uptake efficiency was found in the young roots compared with the old roots. Fertilizer nitrogen applied to Phalaenopsis Sogo Yukidian ‘V3’ roots could be detected in both upper and lower leaves as early as 0.5 day after application, and continued to accumulate in the leaves over the 8-day experimental period. During this period, fertilizer nitrogen only accounted for a small portion of the nitrogen accumulated in the actively growing young leaf, while the bulk came from stored nitrogen. In another experiment where fertilizer nitrogen absorbed during the small, medium, or large plant stages was traced, it was found that regardless of the stage of application during the vegetative period, a similar percentage of the absorbed nitrogen was allocated for inflorescence development. Nitrogen accumulated during the small, medium, and large plant stages contributed significantly to inflorescence development and constituted 16%, 25%, and 59%, respectively, of the stored nitrogen translocated to the inflorescence at the visible bud stage. Reducing fertilizer application during the reproductive stage resulted in increased utilization of stored nitrogen for inflorescence development. Results of the last two experiments highlight the importance of fertilization throughout all stages of Phalaenopsis. Results of the various experiments also indicate the ability of mature leaves and roots of Phalaenopsis to serve as storage organs for nitrogen.