惠蓀林場枯落物養分迴歸量與分解速率之季節變動

Abstract

摘 要 本研究以台灣中部惠蓀林場三種不同林分(天然林、杉木林、次生林)為對象，自2001年1月至2002年12月，利用收集網收集枯落物，調查每月枯落物量，包括落葉、枝條、繁殖體及其它，並分析養分的迴歸量。同時，自2000年4月至2003年3月，使用枝葉袋測定枯落物分解速率，探討三種林分枯落物量及分解速率之動態變化及颱風對本試驗地之影響。 全年枯落物總量，兩年期間皆以天然闊葉林為最高，分別為5,508.3，5,471.0 kg ha-1 yr-1，次生闊葉林為次之，分別為3,664.1，4,885.6 kg ha-1 yr-1，杉木人工林為最低976.6，2,227.1 kg ha-1 yr-1。枯落物量在月份間有極顯著的差異，可區分為雙高峰期，一為3-5月的生長季節，大量老葉被新葉取代而脫落，另一為6-7月的颱風季節，因颱風侵襲而影響枯落物的總量及其成分比例。三種林分枯落物各成分中，皆以落葉量所佔比率為最高佔60.4-76.4 %，枝條佔11-23 %，其餘為繁殖體及其他等物質。枯落物各養分迴歸量，兩年期間皆為天然闊葉林>次生闊葉林>杉木人工林。三種林分之養分迴歸量為碳417.6- 2,250.1 kg ha-1，氮11.9-85.3 kg ha-1，磷1.0-7.5 kg ha-1，鉀5.8-55.6 kg ha-1，鈣5.5-49.8 kg ha-1，鎂2.1-14.3 kg ha-1。 三種林分經三年後，其分解速率以天然闊葉林為最快，杉木人工林和次生闊葉林則相近，其重量留存分別為24.75，38.82，36.00 %，分解常數(k)則在0.32-0.48間。重量留存率呈上下波動現象，是受到有機物及礦物物質污染，造成枯落物損失量的低估，影響分解速率。在養分留存率方面，天然闊葉林和次生闊葉林的所有養分，皆隨著分解時間增加而下降，杉木人工林在氮、磷及鉀隨著分解時間增加有先增後降的趨勢，其餘碳、鈣、鎂、木質素則是隨著分解時間增加而下降。由於木質素初期濃度大於40 %，故三種林分在分解初期時就開始分解。以C/N比來預測氮的淨礦質化作用，當C/N比低於25時，便開始進行淨礦質化作用。

Abstract In this study, the monthly amount of the litterfall, including of leaves, branches, reproduction and other materials, along with the nutrient recycling amount of three different stands (natural hardwood stand, NS; China-fir plantation stand, CPS; and secondary hardwood stand, SS) in the Hui-Sun Experimental Forest were monitored from Jan. 2001 to Dec. 2002 by using littertrap method. At the same time, decomposition rate of litter layer were examined from Apr. 2000 to Mar. 2003 by using litterbag method. The purposes of this study were to evaluate the litterfall and decomposition rate dynamics of three different stands. During two years investigation, the results indicated that the annual amount of the litterfall of NS (5,508.3 and 5,471.0 Kg ha-1 yr-1) was the highest, followed by SS (3,664.1 and 4,885.6 Kg ha-1 yr-1), and that of CPS (976.6 and 2,227.1 Kg ha-1 yr-1) was the least. The significant variations about the monthly amount of the litterfall can be divided into two peaks. One was in the growth season (Mar.-Jun.) during which a large amount of old leaves were replaced by new ones. The other was in the typhoon season (Jun.-Jul.), the monthly amount of litterfall as well as its components were affected by both times and degrees of the typhoons. Among the three different stands of the litterfall, 60.4~76.4 % of which was composed of the foliar litter, 11~23 % of which was the branch, and the remainder was reproduction and other plant material. The nutrient recycling amount of the litterfall of NS was the hightest followed by SS, and that of CPS was the least. Recycling amount of these nutrients contained 417.6-2250.1 Kg ha-1 C, 11.9-85.3 Kg ha-1 N, 1.0-7.5 Kg ha-1 P, 5.8-55.6 Kg ha-1 K, 5.5-49.8 Kg ha-1 Ca, and 2.1-14.3 Kg ha-1 Mg, respectively. After 3 years of decomposition, the decomposition rate was faster in NS, followed by CPS and SS. The remaining mass of litter was 24.75, 38.82 and 36.00 % for NS, CPS and SS, respectively. The annual decomposition constant (k) was ranged from 0.32 to 0.48 at the end of 3 years. The remaining mass of litter fluctuated because the contamination of field litterbags with organic and mineral led to the underestimated litter mass loss and affected decomposition rates. In this study, the percentages of nutrients remaining of all nutrients were decreased with time pass in NS and SS. The N, P and K increased initially but than decreased, and C, Ca, Mg and lignin increased until the study end in CPS. Because of the litter with high initial concentrations (>40 %), decomposition started in early stages of decomposition in three different stands. Net mineralization could be well predicted from the C/N ratio. When the C/N ratio was below 25, N net mineralization would start.