- 學位論文
阿里山地區淋澱化土壤伴隨黏粒洗入之特性化育作用與分類
Soil Characteristics, Pedogenesis and Classification of Podzolic Soils with Clay Illuviation in Ali Mountain
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摘要
在臺灣亞高山地區砂岩或頁岩所風化之細質地土壤中，黏粒洗入伴隨淋澱化作用或具淋澱化特徵的現象於前人研究中已被發現，在淋澱化作用機制上，黏粒洗入並非其生成之要素，因此將對此土壤化育作用進行研究探討。本研究區三個土壤剖面採集自阿里山區萬歲山、小笠原山及祝山林道，海拔高度從2200 m至2500 m，年均溫為10.8 °C，年降雨量約為4,000公釐，氣候終年冷涼潮濕，無明顯乾燥季節，土壤溫度境況屬於溫和，土壤水分境況則屬於潮濕。研究區母質於中新世紀層晚期生成，以砂岩、頁岩互層為主，因此大部分土壤生成之黏粒含量較高。植被以針葉林為主，紅檜 (Chamaecyparis formosensis)、臺灣鐵杉 (Tsuga chinensis) 及臺灣扁柏 (Chamaecyparis obtuse)佔優勢，輔以華山松 (Pinus armandii)與杜鵑(Rhododendron simsii)灌叢社會等，地被植物主要以玉山箭竹(Yushania niitakayanensis)較佔優勢與芒草(Miscanthus floridulus)和一些蕨類及苔蘚類植物。本研究之目的在探討阿里山地區森林土壤生成化育之機制，透過土壤樣體之形態特徵、理化性質、微形態特徵、黏土礦物組成及礦物風化序列，藉以了解該地區土壤間生成過程之差異。 研究結果顯示，從質地分析中可將三個土體分為砂質黏壤土與黏壤土兩類，黏粒含量在漂白層較低，隨深度增加而上升，在B化育層中達到最大量，而到C層漸減。土壤剖面中亦可發現黏粒有向下聚積之現象且同時在淋澱層中進行累積。在化學性質方面，土壤樣體均屬於高度淋洗之強酸性土壤 (pH 3.3-4.9)與低鹽基飽和度 (BSP < 10%)。有機碳主要分布在土壤表層之O或A化育層，淋澱層(Bhs)次之，漂白層(E)含量最低。淋澱層與黏聚層中各型態鐵與鋁含量均明顯高於漂白層(E)，顯示土壤中有多量活性鐵、鋁與有機質形成有機鐵或鋁錯合物型態向下移動堆積沉澱，進而形成暗色或紅棕色等淋澱化物質之淋澱土。有機碳與鐵、鋁之線性迴歸分析具顯著相關，顯示淋澱化物質在土體中移動造成化育作用，而在游離態鐵與鋁與黏粒移動亦有顯著相關。土壤微形態構造觀察結果，漂白層中土壤顆粒間物質多數已被淋洗竭盡，存在多數原生礦物顆粒，少部分暗色有機錯合物殘留於孔隙或孔洞中，藉由溶質將之向下移動。在適當環境下，土壤孔隙或土壤基體上沉澱而生成有機金屬披覆體。除暗色有機錯合物之外，同時可觀察到黏粒披覆體存在於土壤顆粒間隙中，此與土壤物理分析與化學分析結果吻合，意思即為有機物與鐵、鋁以及黏粒移動是可能同時存在於土壤體中。 三個土壤樣體之黏土礦物組成，在漂白層(E)中主要以蛭石、伊萊石及蛭石－伊萊石混層礦物為主，在淋澱層(Bhs)中主要以蛭石含量較豐，且亦有相當量之蛭石－伊萊石混層礦物，同時水化蛭石含量也漸增。推測本研究區內礦物風化序列為伊萊石→蛭石(或蛭石－伊萊石混層礦物)→水化蛭石。 土壤樣體之分類為二類，土壤樣體1501及1503同屬第一類，符合淋澱土的特性，黏粒含量較少為砂質黏壤土，分類上屬極育型簡育正常淋澱土(Ultic Haplorthod)。因此淋澱化作用為主要土壤化育作用。有機碳、黏粒以及各型態鐵、鋁含量在淋澱層或下層達到最大量，顯示淋澱化物質與黏粒在土層中有移動現象。從微形態特徵觀察可發現，在淋澱層土壤中發現有機物複合鐵鋁物質覆蓋在黏粒披覆粗石英顆粒表面上。第二類土壤樣體1502在化學性質雖然具有淋澱化作用現象，但黏粒洗入聚積使得土壤較亮，在分類上以典型簡育濕潤極育土(Typic Hapludult)。同時在Bhs層微形態特徵可見少量有機物與鐵、鋁形成有機態錯合物包覆在礦物粒子的表面或散布於孔隙與孔洞中，而孔隙邊緣與孔洞有黏粒之定位排列，同樣表現出淋澱化作用與黏粒洗入為主要之土壤化育作用，但以黏粒洗入為主，因此應為具淋澱化作用的極育土。 在本研究區所發現之砂質黏壤土或黏壤土之土壤生成作用是以淋澱化作用為主。在地形平坦處砂質區域由於植被較豐富具含量較高之有機酸，導致礦物風化釋出鐵、鋁形成淋澱化物質，同時隨著強淋洗作用伴隨溶質向下移動，促成淋澱化作用發生，此外黏粒洗入可能同時發生或移動較快，導致在土壤中同時觀察到黏粒洗入的現象。
並列摘要
Clay illuviation associated with podzolization or with podzolic features has been found in the subalpine forest soils in Taiwan. It was actually occured in the fine-textured soils derived from sandstone or shale. Clay illuviation is not generally involved in the mechanism of Podzol soil formation process. Three soil pedons were separately sampled at Wansueishan, Ogasawara and Chushan Mountains. The study area is located at near 2400 meters elevation with annual rainfall near 4000 mm. The soil temperature regime is mesic and the soil moisture regime is udic. Coniferous vegetations are the dominant with Taiwan red cypress (Chamaecyparis formosensis), Chinese hemlock (Tsuga chinensis) and Taiwan cypress (Chamaecyparis obtuse) in this area. The minor shrub communities are pine (Pinus armandii) and Rhododendron (Rhododendron simsii). The ground is covered mainly by Yushan bamboo (Yushania niitakayamensis), miscanthus (Miscanthus floridulus) and some mosses. The objectives of this study were performed by soil morphological characteristics, physical and chemical properties, and mineral composition to study the unique soil formation processes in podzolic soil combined with clay illuviation in the subalpine forests. The results indicate that the soil texture of three pedons can be distinguished into two groups, one is sandy clay loam and the other one is clay loam. Clay contents were the lowest in the albic horizon. The clay illuviation is significantly increased in the upper part of B horizon of the Podzols, and then decreased in the C horizon. We also observed clay was moved downward and accumulated both in argillic horizon and spodic horizon. Soil chemical properties show that soil is strong acidity (pH 3.3-4.9) and very low bases saturating percentage (<10%). The soil organic carbon is mainly distributed in topsoil because the higher humus is not easily decomposed by microorganism, low temperature and coniferous vegetation. The content of organic carbon and different forms of Fe and Al were significantly higher in spodic and argillic horizon than those of albic horizon, which is indicated that large amount of active amorphous and organic-sesquioxide materials were accumulated in the soil. Podzolization processes were characterized by the accumulated organic carbon, Fe, and Al in spodic horizon, therefore we can find the significant correlations among organic carbon, Fe and Al content in the E and B horizon (p<0.01). Distinct organo-iron complexes materials and clay coatings were accumulated on the coarse grains of the Bhs horizon by polarized microscopy. Except of the dark pellets of organic compounds, the slightly oriented clay coating also appeared along the soil pores and channels. Therefore, pedogenic processes in the study area are mainly characterized with the illuviation of organo-metallic (Fe and/or Al) complex materials and fine clay particle. The clay mineral compositions of three pedons in study area can be divided into two parts due to the horizon differentiation. The albic horizon was prominent with illite, vermiculite and vermiculite-illite interstratified minerals. The other part is mainly consisted of much more vermiculite, vermiculite-illite interstratified minerals and hydroxy-interlayered vermiculite (HIV) in the spodic and argillic horizons. The weathering sequence of clay mineral of Podzols with fine textures in the study area is proposed as: from illite to vermiculite, then to HIV and vermiculite. As the results, two of three studied soil pedons can be classified as Ultic Haplorthod or Typic Haplorthod and the other one pedon can be classified as Typic Hapludult based on USDA Soil Taxonomy. We proposed that clay illuviation was one of the pedogenic processes in the study area. However, podzolization was only formed at the area with gentle slope or flat landscape to promote the strong leaching process with very high precipitation in the study area. To consider the environment condition with the dense coniferous vegetation dominated at the study area, the weathering time of podzolization is the main pedogenic process factor that leads to the soil transition. Overall, the phenomena of pedogenic processes both podzolization and clay illuviation could be observed together in flat landscape region of Ali Mountain.
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