竹園紅樹林生態營養物質流轉之動力學研究

Abstract

竹圍紅樹林沼澤地位於淡水與竹圍間的淡水河畔。本地區共有12科25種植物，但僅水筆仔（Kandelia candel L. Druce）屬於紅樹科(RhizoPhoraceae)為紅樹林植物，餘則為其他常見的海邊植物。水筆仔為構成紅樹林的主要樹種，生長於潮間帶，其他植物則生長於潮水不易到達的地方。依沼澤地的植被與潮水沖擊程度的不同，筆者將此地區劃分為潮溪紅樹林區，河邊紅樹林區、混生林區、草生地區及河邊沙灘地區等六區。潮溪紅樹林區與河邊紅樹林區之水筆仔林生長良好，其平均落葉量為1.83g/m平方公尺/day。其落葉具週期性，於八月颱風過境時，落葉量高達7.7g/m平方公尺/day，四、五月因當地氣溫上升，落葉量可達2~3g/m平方公尺/day，其他月份則維持在1g/m平方公尺/day左右。由水筆仔生育過程的觀察顯示其為適合生長於溫度低於20℃的種類。由土壤分析結果顯示水筆仔生長較好的潮溪紅樹林區的土壤質地為坋壤土，其有機質含量、總氮量、有效磷量及陽離子交換量均較其他地區高，且已具適合紅樹林生長的最佳條件。由潮水分析結果顯示，潮水可供給紅樹林生長所需的多量元素，而紅樹林則提供海水中所缺乏的氮化合物和磷化合物，而有利於海中生物生長。由水筆仔葉片營養分析結果顯示幼葉中含有較高量的氮、磷、鉀，而老葉中則含有較高量的鈉、鎂、鈣。潮溪紅樹林區的水筆仔葉片中含有較高量的氮和磷，且其氮:磷:鉀的比值類似幼苗葉片中者，介於2.5~3.0：0.28~0.33：1。矮小紅樹林區的水筆仔葉片中，氮和磷的含量與氮：磷：鉀的比值均偏低，與其生長的土壤中含有的氮和磷偏低的結果成正比。水筆仔體內含有大量的鈉，尤以老葉的含量高，顯示水筆仔可藉老葉掉落的方式來排除體內過多的鈉鹽。由水筆仔葉片中游離態胺基酸的含量分析，顯示水筆仔並未以堆積大量的proline來適應其生長的鹽分地。

The Chuwei mangrove swamp is situated at the estuary of Tanshui river. Floristically, 25 species belonging to 16 genera and 12 families are found here. Kandelia candel, a member of Rhizophoraceae, is the only mangrove species locally, the remainders being common seaside plants. K. candel is also the dominant species in the swamp. It grows in the intertidal zone, while other seaside plants occur in areas free of tide. According to the degree of tidal action and the difference in floristic composition, the swamp was arbitrarily classified into six areas, i.e., tidal creek mangrove area, riverine mangrove area, mixed species area, grassland area, dwarf mangrove area, and sandy beach area. The average leaf fall rate of K. candel forest in the tidal creek mangrove area and the riverine mangrove area was 1.83g/m^2/day. The leaf fall rate correlated well with climate. During the period of 1982-1983, the rate was relatively stable, being about 1g/m^2/day in most months. A higher rate of about 2-3g/m^2/day was obtained in April and May, owing to the raise of air temperature. The rate reached a maximum of 7.7g/m^2/day in August as a result of the occurrences of typhoon. K. candel grows luxuriously in winter when the air temperature is below 20℃. The results of soil analyses indicate that the soil sampled from the creek mangrove area is silt loam with high contents of organic matter, total nitrogen, available phosphate, and high cation exchange capacity, thus providing favorable conditions for the mangrove growth. The results of tidal water analyses reveal that tidal water can offer macro-nutrients which sustain the productivity of mangrove. On the other hand, the mangrove swamp contains high contents of nitrogenous and phosphatic compounds which benefit marine habitants in the estuary. The mineral contents of K. candal seedlings vary with plant parts. High contents of N, P, and K are found in young leaves, whereas in older leaves, high level of Na, Mg, and Ca are observed. The contents of N and P in leaves of K. candel is lower in the dwarf mangroves area. This seems to be correlated with the low level of N and P in the soil. The ratio of N:P:K found in young leaves is close to that in old leaves regardless of the location of sampling area. K. candel can accumulate high level of Na, especially in older leaves. The results of free amino acid analyses in leaves of K. candel indicate that the concentration of proline is not high enough for interpreting the adaptation mechanism of K. candel in the saline environment.