溪頭人工針葉林淨初級生產力與土壤溫室氣體釋放

Abstract

本研究目的為探討溪頭營林區4個人工針葉林包含25年生台灣杉 (TC88)、32年生巒大杉(CL81)、34年生巒大杉(CL79)及42年生柳杉 (CJ71) 森林淨初級生產力 (Net primary production, NPP)，以及施加硝酸銨 (NH4NO3) 150 kg N ha-1，對於NPP之影響，在CL81以密閉罩法 (Closed chamber method) 測量三種溫室氣體 (N2O、CH4、CO2) 施肥後的釋放，以及量測土壤水溶液中離子濃度、電導度及pH值，觀察施肥後養分動態變化，最後將三種溫室氣體及NPP轉換成GWP (Global Warming Potential)，評估施肥對於之整體影響。 研究結果顯示，在NPP部分，4個樣地平均為8.7 ± 3.7 Mg C ha-1 yr-1，施肥後NPP都沒有顯著差異 (p>0.05)。在溫室氣體部分，N2O在施肥後第5天施肥樣區與未施肥樣區相比，釋放有顯著差異 (p<0.05)；CH4在施肥後第15天釋放有顯著差異 (p<0.05)；CO2釋放則在施肥後沒有顯著差異。在土壤溶液部分，土壤溶液pH值受到施肥影響，在2012年1/21施肥後，3、4、5月施肥樣區與未施肥樣區相比皆有顯著差異(p<0.05)；土壤溶液電導度在2、3、4、5月施肥樣區與未施肥樣區相比有顯著差異；土壤溶液離子部分，NO3--N濃度在2012年2、3、4、5月有差異，而NH4+-N濃度則在施肥後沒有顯著差異。 總結來說，在施肥後的一年內，林分可能受限於針葉樹的生長速度較為緩慢或是林地內存在非氮元素之外的生長限制因子，因此對於NPP並沒有顯著影響。但是若轉換成GWP來看，溪頭巒大杉人工林施肥之後，NPP及GHGs雖未達顯著標準，但對於溫室效應無負面影響。

The purposes of this study were two. The first was to estimate net primary productionand fluxes of three greenhouse gases includingN2O, CH4 and CO2 of coniferous plantations in Xitou Experimental Forest. The second was to compare changes of net primary production and greenhouse gases emission in unfertilized and fertilized plots with NH4NO3 (150 kg N ha-1).There were four sitesin Xitou including the plantations planted Taiwania cryptomerioides in 1988 (TC88), Cunninghamia lanceolata var. konishii in 1981 (CL81) and 1979 (CL79) as well asCryptomeria japonica in 1971 (CJ71).Soil solutions also gathered to analysis amount of NO3--N, NH4+-N, conductivity and pH after fertilization in CL81. Finally, we transmitted NPP, fluxes of greenhouse gases to Global Warming Potential to assessed effects of fertilization in CL81. Results of NPP in TC88, CL81, CL79, and CJ71 averaged 8.7 ± 3.7 Mg C ha-1 yr-1 and showed no significant different between unfertilized and fertilized plots. The flux of N2O showed significance difference between unfertilized and fertilized plots in the 5th dayafter we added NH4NO3. On the other hand, there was significance difference of the flux of CH4 between unfertilized and fertilized plots in the 15th day after fertilization. But there was no significance difference of the flux of CO2. Conductivity and NO3--N concentration in soil solution were significance difference between unfertilized and fertilized plots in February, March, April and May. The pH value of soil solution was significance difference between unfertilized and fertilized plots in March, April and May. However, there was no significance difference in NH4+-N concentration after nitrate ammonium addition. In conclusion, we speculate about the reasons for no significance differences of NPP after fertilization are that the growth of conifer is slow and there are other limiting factors, which restrict the growths of stands. Although the results of GWP and GHGs are not significance between control and fertilization, there areno negative effects on global warming.