文心蘭對氮之吸收與氮於植體內之分配

Abstract

文心蘭為臺灣第二大蘭花產業，以外銷切花為主。其膨大且富含養分的假球莖具世代相連的特性，增加營養研究上的難度。本研究藉由穩定性氮同位素追蹤法，暸解文心蘭對肥料氮的吸收與偏好，以及自肥料中吸收的氮於植體內分配之情形。期能改善業界於文心蘭生育階段間之施肥技術，提升切花品質，增進農民收益。 施肥後12小時，肥料氮即可被根部吸收並運移至植體各部位。文心蘭根部、葉片及假球莖組織中皆含有硝酸還原酶，並以根部活性最高，葉片活性次之。隨根齡增加，根部硝酸還原酶活性逐漸下降。栽培於日夜溫25/20 oC環境下之文心蘭，根部之硝酸還原酶活性最高，有利植體對氮素之吸收。同時給予尿素、銨態氮與硝酸態氮三種氮源時，文心蘭根部吸收三種氮源之比例為0.75：0.57：1，顯示文心蘭偏好吸收硝酸態氮。 新芽萌發期與新芽生長期為文心蘭之營養生長期，該時期吸收之肥料氮主要供給當代假球莖發育，其餘氮則儲存在較老之假球莖中，並於生殖生長期將氮分配至花梗供其發育。於假球莖出鞘期與假球莖成熟期，文心蘭進入生殖生長期，該時期吸收之肥料氮大多供給花梗發育，其餘氮素則儲存於各代假球莖中。顯示花梗發育所需氮源，大部分來自生育週期後期所吸收之肥料氮。待進入下一世代之生殖生長期，文心蘭花梗發育所需的氮，一部分來自上一世代的儲存氮，而大部分則來自當世代生殖生長期所吸收之肥料氮。 綜合上述，文心蘭根部之硝酸還原酶活性最高，對氮之吸收偏好硝酸態氮，故於根部施肥時可提高硝酸態氮之比例，且於日夜溫25/20 oC下栽培，有利文心蘭吸收氮素。目前業界傾向於文心蘭生殖生長期減少氮肥的施用以增加抽梗率，然本研究發現，文心蘭花梗發育所需氮源，大部分來自生殖生長期給予的肥料氮。故文心蘭生殖生長期間更應注重氮肥的施用，以利文心蘭切花生產品質及植株下一世代之發育。

Cut flower production of Oncidium is the second largest orchid industry in Taiwan. The enlarged pseudobulbs, which store nutrients and are interconnected between generations, present difficulties in nutrition research. In this study, the stable isotope of nitrogen was used as a tracer to understand how Oncidium absorbs nitrogen in the fertilizer, nitrogen be allocated in the plant, and the nitrogen form it prefers. It is hoped that the results of this study will provide useful information for improving the fertilization management of Oncidium at different growth stages, so that the quality of Oncidium Gower Ramsey cut flower and the earning of growers may be increased. After 12 hours of application of fertilizer, nitrogen can be absorbed by the roots and translocated to various parts of Oncidium Gower Ramsey. The leaves, tissue of pseudobulb, and roots of Oncidium Gower Ramsey all have nitrate reductase activities. The activity was highest in the roots, and second highest in the leaves. The nitrate reductase activity of roots decreased with increased age of roots. Under 25/20 oC day/night temperature, the nitrate reductase activities in root of Oncidium was the highest, and it was favorable for Oncidium to absorbed nitrogen. When three kinds of nitrogen sources of urea, ammonium, and nitrate were given at the same time, the roots of Oncidium Gower Ramsey absorbed the three nitrogen forms in the proportion of 0.75：0.57：1, indicating that nitrate was the preferred form of nitrogen for absorption by the roots. Bud stage and plantlet stage are the vegetative stage of Oncidium Gower Ramsey. Fertilizer nitrogen supplied during the vegetative stage of Oncidium Gower Ramsey was used mainly for the development of the current pseudobulb. The remaining nitrogen was stored in the older pseudobulbs. The nitrogen stored in the pseudobulbs at the vegetative stage was partially allocated to stalk for its development during the reproductive stage. Unsheathing stage and pseudobulb with inflorescence stage are the reproductive stage of Oncidium Gower Ramsey. Most of the fertilizer nitrogen supplied during the reproductive stage was allocated to support stalk development, while the remaining was stored in the pseudobulbs. It indicated that the main nitrogen source of inflorescence was from the nitrogen absorbed during the later phase. During the reproductive stage of the next generation, the nitrogen allocated to the stalk came partly from nitrogen stored in the previous generation, while the majority came from the nitrogen absorbed during the reproductive stage of the current generation. In summary, the nitrate reductase activity of roots was the highest among organs of Oncidium Gower Ramsey, and roots preferred nitrate in nitrogen uptake. Therefore increasing the proportion of nitrate is recommended for fertilization applied to the roots. Under 25/20 oC day/night temperature, it was favorable for Oncidium to absorbed nitrogen. Reducing the application of nitrogen during reproductive stage is commonly practiced by growers with the intention to increase the rate of stalk emergence. However, this study shows that the source of nitrogen for development of the stalk came mostly from fertilizer applied during the reproductive stage. Therefore, it is important to continue the supply of nitrogen during the reproductive stage of Oncidium Gower Ramsey to improve the quality of cut flower produced and the development of the next generation.