南仁山低地雨林凋落物分解之研究

Abstract

本研究以墾丁國家公園南仁山保護區之低地雨林組成樹種為對象，在前人設置之永久樣帶上選取12種樹種（小葉木犀、高士佛赤楠、嶺南椆、金平氏冬青、南仁山新木薑子、革葉冬青、山龍眼、白榕、茄苳、印度栲、南仁鐵色、九節木），並分別在樣帶選取三個海拔位置，設置16個樣方，進行分解袋實驗，以瞭解主要組成樹種之葉片在樣帶不同位置上分解的情形，並探討其營養釋出與氣候、環境、及凋落物特性之關係。 經由土壤剖面調查結果得知，土壤質地方面以溪穀區（海拔250公尺）之粒含砂量最高，隨海拔上升，砂粒含量逐漸下降；黏粒含量與砂粒含量分佈呈反向分佈。山頂土壤質地介於砂質黏壤土及黏壤土間，溪穀則屬砂質黏壤土。pH值由溪穀、中段至稜線分別為5.03、4.91、4.93。經由淋洗及陽離子交換容量實驗測得：陽離子（鉀、納、鈣、鎂）總含量以溪穀區最高、中段次之、稜線最低；飽和鹽基百分比以溪穀最高，山頂最低；有機物含量亦以溪穀區最高，其次為中段，最低為稜線區。土壤調查結果顯示溪穀土壤養分含量較山頂優沃。 分解袋實驗中，稜線區所選取之樹種以金平氏冬青之葉片分解速率最快，嶺南椆最慢，半衰期分別為125及251日；中段樹種則以南仁鐵色葉片分解速率最快，山龍眼為中段最慢，半衰期分別為146及276日；溪谷區以白榕的葉片分解速率最快，印度栲最慢，半衰期分別為100及349日。第一季（春季）及第二季（秋季）置放之葉片分解率有明顯差異。 就濃度變化而言，各樹種葉片養分釋出以鉀元素釋出最快，其次為鈣、鎂，氮素濃度在分解過程中則有升高的趨勢。由於養分釋出總量與重量分解率有密切關係，氮素與重量的相關性尤高，因此，氮素仍以稜線區的金平氏冬青、中段的南仁鐵色、溪谷區的白榕、茄苳的釋出速率最高。第二次放置之葉片釋出氮素之種間趨勢雷同。第一季實驗中，各樹種除南仁山新木薑子外，葉片中留存率在第67天已降至50％以下；第二季實驗中，鉀流失率減緩，第92天時，大部分樹種之留存率才降至50％以下，種間趨勢與第一季表現不盡相同，顯示雨季與乾季之差異明顯。鈣及鎂的流失率呈現較不規則的趨勢，各樹種之間差異甚巨。

The purpose of this study is to understand decomposition rate of dominant species and nutrient input to forest floor under disturbances along transect set three years ago. Leaves of three to four dominant species of summit, lower backslope and footslope of transect and two wide-distributed species were collected to proceed decomposition experiment. Leaves of wide-distributed species were taken to test the habitat variation of three sections of the transect while leaves of dominant species of each section were taken for decomposition rate of litter with different quality. According to soil investigation, soil text of summit is classified into clay loam while soil of footslope is sandy clay loam. Total cation content, BSP and pH are lower in summit than in footslope position. Decomposition rates of wide-distributed species (Drypetes hieranensis (Hayata) Pax, Psychotria rubra (Lour.) Poir.) in three section of transect exhibit no difference among sections in both experiments started from March and September. Leaf litter of Ilex triflora, Drypetes hieranensis, and Ficus benjamina decomposed more rapidly than other species in each section, respectively. Half life of these three species are 125,146,100 days for first experiment and 180, 160, 143 days for second experiment. Nutrient releasing patterns are different among ions traced. Nitrogen is released as litter being decomposed. Remaining percentage of potassium and magnesium in litter reached stable percentage after decomposing for 100 and 150 days. Calcium releasing pattern fluctuated with time and reached low remaining percentage after 150 to 200 days. Ficus benjamina produces highest litter under both disturbed and non-disturbed condition and has highest decomposition rate on footslope while Cyclobalanopsis chamionii with highest litter productivity decomposed most slowly among elected species on summit. This indicate higher nutrient flux on footslope than on the summit. With addition of soil character, footslope has better condition for growth of plants.