腦寮溪天然闊葉林枯落物與林地養分動態之研究

Abstract

本研究以腦寮溪天然闊葉林為試驗地，自2001年8月至2003年3月，調查森林枯落物量及其養分含量、枝葉層分解速率及其養分留存率、土壤養分庫，以探討林地有機質和養分由植體進入枝葉層、土壤層的動態變化。 本試驗地的年枯落總量為9.14 t/ha，各組成分量的高低依序呈葉部>枝條>其他>繁殖體。枯落物總量的季節性變化，總量主要受葉部影響而隨之變動，呈春初夏末為最高量的單一高峰型的凋落類型。於試驗期間枯落物量因受“娜克莉”颱風的影響，使得此月無論是在枯落物總量或枯落物養分含量均達最高，尤其是影響枯落物組成分中的枝條，顯著高於其他月份枝條的枯落物量，達5-114倍之多。 枯落物各組成成分的養分濃度以其他部位濃度最高，繁殖體次之。養分濃度高低呈碳>氮>鈣>鉀>鎂>磷>鈉>鐵>錳濃度，而各組成成分養分濃度的月變動情形大致呈春末4-6月及秋末10-1月是養分濃度出現的高峰時期。枯落物養分年輸入量，均以葉部顯著高於其他各個組成分，顯見葉部為林地養分回歸主要來源。 枝葉層分解速率受分解期間雨量分布不均影響，致使分解的第190天至245天為枯落物分解最迅速時期，有隨著雨量的增加重量留存率的增減量亦有相似的變化趨勢。分解過程中枯落物組成成分的動態變化，顯示氮、磷、鈣、錳、鐵及硫濃度會隨分解時間增加而增加；碳及鎂濃度則隨分解時間增加而遞減；鉀及鈉濃度則於初期呈逐漸下降，而後突然有升高的趨勢。 枝葉層養分濃度受枯落物的原始養分濃度高低影響，於月份間的變動以鎂、磷、鈉、鉀、鈣及錳濃度均呈顯著差異（P<0.05）。枝葉層的養分含量分布狀態主受枝葉層重量而定，均呈H層>F層>L層，有顯著隨土壤層加深而增加的明顯趨勢。土壤養分濃度與含量高低之季節變動，顯示8月份的養分濃度最高，而4月期間最低。土壤養分濃度及含量的高低會隨土壤層的加深而遞減，且多集中於0-10 cm的土壤層中。

The purpose of this study was to explicate how the nutrient dynamics of forest from vegetation to soils changed. The content and concentration of litterfall, litter decomposition and soil nutrient pool were investigated monthly from August 2001 to March 2003 in the natural hardwoods of the Nao-Liao River. The amount of litterfall produced in this site was 9.14 t/ha yearly. Most of the litterfall were composed by leaves, followed by branch, others and reproduction. The seasonal variability of litterfall showed a uni-modal distribution pattern. In this study period, the litterfall variability was due to the strong typhoon , Nakri, which might have led to increased more than 5 to 114 times branch litter compared with other months. Nutrients concentration of litterfall was in the order as C>N>Ca>K>Mg>P>Na>Fe>Mn, and the concentration of litterfall was highest in others, followed by reproduction. The seasonal variability showed the highest during later spring(April-June)and later autumn(October-January). In addition, nutrient returned to the soil through litterfall among different component was greatest in leaves. Leaf litter decomposition rate in this site was affected by rainfall, and showed rapid rate during the 190th to 245th days. The decomposition rate and dynamics of remaining were affected by rainfall distributtion. Nutrient dynamics during decomposition indicated that the N, Ca, Mn, Fe and S concentration were increased until the study ended, the C and Mg concentration was decreased, K and Na concentration was decreased initially but then increased. Nutrient concentrations of litter layer were determine by the initial nutrient composition of litterfall. The Mg, P, Na, K, Ca and Mn concentration of litter layer were varied significantly(P<0.01)each months. The nutrients content were mainly determined by the litterfall mass, and their content was decreased in order: H layer>F layer>L layer. Nutrient concentrations and content of soil were decreased with soil depth and mainly distributed in the 0 to 10 cm soil depth, it showed that maximum nutrients concentration occurred in August and minimum in April.