人工濕地中影響落葉分解率因子的探討：以季風型台灣地區為例

Factors influencing leaf litter decomposition rates in constructed wetlands: A case study in monsoonal Taiwan

彭立言(Li-Yen Peng)

指導教授 ： 任秀慧

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02493

摘要

落葉提供支持濕地食物網的外來能量，其分解對於生態系中營養和碳的循環至關重大。人工濕地在世界各地被廣泛地建造，作為因人為活動破壞自然濕地的異地補償。因此在監測人工濕地補償成果時，需要簡單且通用的指標來評估人工濕地的生態功能。落葉分解速率和濕地中的營養循環及有機質累積有關，也影響著碎屑提供、碳儲存及支持異營食物網等濕地生態系統服務。雖然熱帶亞洲地區大部分的自然濕地受到人為活動的嚴重損害，此地區關於人工濕地落葉分解率的研究卻很少。本研究目的為探討水質參數變化和落葉特性(葉品質和葉密度)在人工濕地對於落葉分解速率的影響。落葉分解實驗進行於打鳥埤人工濕地和新海二期人工濕地各三個池子中，於2011年春季和秋季量測水質參數和分解速率的變化。本實驗比較單一葉種和混合葉種分解速率的差異，也分別設置三種不同密度(高、中、低)的葉包以檢驗葉密度對於分解速率的影響。單一葉種(SS)使用開卡蘆，混合葉種(MS)則包含了開卡蘆、蘆葦、空心菜和台灣水龍。此外也進行葉片的葉品質(物理化學性質)分析以探討葉品質的差異對分解速率造成的影響。研究結果顯示，水質參數和落葉分解率相關性低(R2 = 0.1456)。因為人工濕地的環境營養鹽濃度高，所以營養變化對於落葉分解率沒有明顯的影響。葉品質分析結果顯示MS實驗處理因為加入較高品質的空心菜和台灣水龍而有較高的N、P含量和較低的木質素，MS實驗處理分解速率在春季顯著高於SS實驗處理(>1.5倍)，顯示高葉品質的葉片有較高的分解速率。在秋季，MS和SS實驗處理的分解速率沒有顯著差異。這可能和秋季顯著較高的水溫有關(25˚C) ，前人文獻亦指出當水溫升至20˚C以上，纖維素和木質素的分解會增加，這使其對於葉分解的負面影響降低。此外，高密度的葉有較高的分解速率，但這需要進一步的實驗來確認為生物對於落葉分解的影響所致。本研究提供了開卡蘆的分解速率和亞熱帶地區影響落葉分解率因子的資料，證實葉品質和葉密度對落葉分解速率的影響較水質參數的影響較大。我們可利用葉品質對落葉分解速率進行初步的預測，但建議環境因子的影響也必須同時監測。由於其在操作上的便利性，落葉分解速率的監測在未來能夠成為監測評估濕地狀況的常用指標。

關鍵字

分解速率 ； 葉品質 ； 混合葉 ； 葉密度 ； 功能性指標

並列摘要

Leaf litter input provides essential allochthonous energy to support the wetland food webs, and their decomposition is crucial to nutrient and carbon cycling in this heterotrophic ecosystems. Constructed wetlands have been widely established in many parts of the world as ex-situ compensation sites for degraded natural wetlands. Simple and holistic indicators are needed to monitor the ecosystem functions of constructed wetlands as the assessment of their compensation success. Leaf litter decomposition rate could be an appropriate functional indicator because it is strongly related to nutrient retention and cycling in wetlands. It also corresponds to many wetland functions including detritus provision, carbon storage, and support of heterotrophic food webs. However, little studies have been undertaken for the leaf litter decomposition in constructed wetlands particularly for the tropical Asian region where most natural wetlands have been heavily impaired by human activities.
In this study, we aimed to determine the influences of environmental factors and leaf litter characteristics (i.e. leaf quality and quantity) on leaf litter decomposition rates in constructed wetlands using field manipulation experiment of leaf litter bags at two constructed wetlands from northern Taiwan including Daniaopi Constructed Wetlands (DN,打鳥埤人工濕地) and Hsinhai Bridge Constructed Wetlands Phase 2 (HS2,新海二期人工濕地). We investigated the decomposition rates of leaf litter from two different experimental treatments including single species treatment (SS) and mixed species treatment (MS), at three different density levels of leaf litter (H; M; L) in three ponds from each wetland site during both spring and autumn in 2011. Leaves of Phragmites vallatoria was used for SS whereas leaves of P. vallatoria, Phragmites australis, Ipomea aquatica, and Ludwigia × taiwanensis were used for MS. The physical and chemical characteristics of all leaf species were also analyzed to determine the importance of leaf quality on influencing leaf litter decomposition rates. Our results showed that water chemistry parameters were poorly related to leaf litter decomposition rates (R2 = 0.1456). Environmental nutrient levels had negligible effect on leaf decomposition rates throughout the study period in the highly nutrient enriched environment of constructed wetlands. Results of leaf quality analysis showed that MS had higher N, P content and lower lignin, cellulose concentration as compared to SS due to addition of species with higher leaf quality (I. aquatica and L. × taiwanensis) in MS. Decomposition rates for MS were over 1.5 times higher than SS in spring, which was consistent to previous literatures that leaf litter with higher leaf quality decomposed faster. However, MS and SS had no significant difference in decomposition rates in autumn. The seasonal difference in treatment effects between MS and SS could be accounted for the significant difference in water temperature between spring (18.6–25.1˚C) and autumn (22.4–28.4˚C). Higher water temperature in autumn thus diminished the negative effect of lignin, cellulose, and toughness to leaf litter decomposition by enhancing biochemical decomposition. In the treatment of three density levels, leaves in H density leaf bags decomposed significantly faster than M and L densities. Our results confirmed that stronger effect of leaf litter characteristics (leaf quality and leaf density) on influencing leaf litter decomposition rates as compared to water chemistry parameters. Initial prediction of leaf litter decomposition rates could be made based on the quality of leaf litter species. We suggested that leaf litter decomposition rates could be an appropriate functional indicator to access wetland condition.

並列關鍵字

breakdown rate ； leaf quality ； mixed leaf ； leaf density ； functional indicator

參考文獻

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