鴛鴦湖生態保護區優勢植物葉營養元素比較

Foliar Nutrient Dynamics of Five Dominant Plant Species in Yuanyang Lake Nature Preserve, Taiwan

鴛鴦湖生態保護區位於台灣亞高山帶，其植物組成可分為森林植物社會和水、濕生草本植物社會。本文分析此保護區內兩種森林優勢植物（台灣杜鵑、台灣扁柏）和三種水、濕生草本植物（芒草、水毛花、東亞黑三稜，合稱沼澤植物）其葉所含之營養元素。主要目的在比較此五種優勢植物其成熟葉以及老葉主要營養元素（氮、磷、鉀、鎂）之季節性變化。相較於台灣杜鵑和台灣扁柏，沼澤植物其成熟葉具有較多的氮、磷和鉀。在所分析的營養元素中，僅鎂元素具季節性變化：五種植物之成熟葉和老葉其鎂含量在春季（四月）時均呈現大幅增加，顯著高於七、十和一月時葉內鎂含量。五種植物黃化老葉其氮、磷和鉀含量均顯著低於成熟葉，顯示葉子在掉落前其營養元素有流失或被移轉的現象，其中以鉀元素含量減少最多。沼澤植物其老葉所減少之磷元素比例顯著高於台灣杜鵑和台灣扁柏。

The vegetation composition of Yuanyang Lake (YYL), a subalpine natural preserve in Taiwan, could be divided into two major communities, the coniferous-hardwood and the swamp communities. Nutrient contents of N, P, K and Mg in mature and senescent leaves of Chamaecyparis obtuse var. formosana and Rhododendron formosanum, dominating the coniferous-hardwood community, Sparganium fallax, Schoenoplectus mucronatus subsp. robustus, and Miscanthus transmorrisonensis, the swamp community, were measured in April, July and October of 2002 and January of 2003. The objectives of this study were to compare the seasonal changes in nutrient contents of leaves among the five species and to determine the extent of nutrient loss in these species prior to leaf fall. In general, mature leaves of marsh plants had higher N, P and K contents than those of the two terrestrial plants. Among the nutrients measured, only Mg contents showed consistently seasonal trend. Mature and senescent leaves of the five species had consistently higher Mg contents in April than those collected in other seasons. In comparison between mature and senescent leaves, senescent leaves always had significantly lower N, P, and K contents than mature leaves, indicating loss of these nutrients from aging leaves. Potassium was the greatest among the nutrients lost. In comparison between terrestrial and marsh plants, senescent leaves of marsh plants lost significantly more P than those of the two terrestrial plants.