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  • 學位論文

中台灣孟宗竹根呼吸及其溫度敏感度

Root respiration and its temperature sensitivity in Moso bamboo, central Taiwan

指導教授 : 久米朋宣

摘要


森林土壤呼吸所排放的二氧化碳,其占所有森林總GPP 50%以上,為第二大生態系碳排放來源;而自營呼吸在前人研究中顯示其碳排放量佔土壤呼吸30–70%,是土壤呼吸中不可忽略的一大部份;近來來孟宗竹的擴張成為了東亞的一大課題,前人研究顯示,在台大實驗林的孟宗竹的土壤呼吸以及土壤呼吸對溫度的敏感度高於其他氣候帶森林,而在在全球溫度逐年升高的情況下,孟宗竹將對碳循環有所影響。 本研究最大的目的為估計孟宗竹林土壤的自營呼吸在總土壤呼吸的貢獻量和找出孟宗竹土壤呼吸的高溫度敏感度的控制因子;為達此目的,此研究有四個小目的;一利用Core sample法Trenching法推估異營呼吸和自營呼吸以及不同型態根的年碳排放量;二了解自營呼吸以及不同型態根呼吸其對溫度的敏感度的高低,並且了解室外(Annual Q10)以及室內實驗(Lab Q10)的差異;三找出其自營呼吸在溫度敏感度的影響因子,此篇實驗利用碳氮元素分析去做解釋;四利用roots order法檢視細根在此篇研究的定義是否可行。 從2014年3月到2015年2月,此研究利用了兩種方法來分離自營呼吸和異營呼吸,分別是Trenching 和 Core sample,在Core sample 的方法中除了可分離自營呼吸外,還可細分其不同型態根的呼吸(細根、粗根、地下莖),而在靠近孟宗竹林附近的柳杉林同樣也進行core sample 的實驗;在core sample的實驗中,除了進行室外的實驗測量,為了確定溫度對於根呼吸的影響,此研究進行了室內實驗(Incubation法),利用這兩種方法來計算細根、粗根、地下莖以及總體自營呼吸的Q10;除此之外利用core sample所蒐集的根樣本除了帶回來進行室內的實驗外也測定了不同類型根的單位面積乾重以及氮含量。為了瞭解細根的定義在此篇的可行性,我們進行root order法的實驗,分出不同的root order根樣本並且測量其粒徑、呼吸量、氮含量; 在孟宗竹中自營呼吸分別在兩種方法中佔了62% - 65%於土壤呼吸,其年排放量大約是501 - 587 g C m-2yr-1,其對土壤呼吸的貢獻比例和年排量皆大於同氣候帶的溫帶森林和闊葉樹林。,而細根年碳排放量約為317g C m-2yr-1、粗根為184 g C m-2yr-1地下莖為54 g C m-2yr-1;細根呼吸佔了約55%的自營呼吸; 為了隔離溫度以外的因子做為控制因素,我們進行了Incubation,發現根呼吸會隨著溫度上升而增加,而其呼吸對溫度的敏感度則會下降;而不同季節的根呼吸溫度敏感度也不同,其Q10在夏秋之季擁有比較高的值。在trenching和cores sample 兩個方法中,自營呼吸的Q10 (=3.61-3.92)比異營呼吸(2.45-2.84)來的大,而細根呼吸在整個自營呼吸中擁有最大的溫度敏感度(4.95)其值高於粗根(3.74)以及地下莖(0.19)且也發現細根呼吸的溫度敏感度有季節性的變異,在進行氮含量分析時,比起粗根及地下莖,細根有最高的氮含量,除此之外,其氮含量也有明顯的季節變異,其趨勢與細根Q10季節性變異相似。可以推斷其細根可能為土壤呼吸高敏度的重要關鍵,而其原因可能為細根的高氮含量。 在root order的實驗中,發現孟宗竹order 2 和order 3的根呼吸有明顯的差距,而root order的粒徑為3.1mm,與此篇研究的細根定義相去不遠(2 mm),因此在此篇細根的定義是可行的。 整體而言,我們了解到自營呼吸為其孟宗竹高土壤呼吸以及溫度敏感度的一大部分原因,細根可能為最重要的影響關鍵。

關鍵字

根呼吸 自營呼吸 溫度敏感度 Q10 孟宗竹

並列摘要


CO2 released by soil respiration (Rs) accounted for about 50% of GPP at the global scale and Rs is the second largest carbon emission in the ecosystem. Rs consist of soil autotrophic respiration (Ra) and soil heterotrophic respiration (Rh), and Ra may account for 30 – 70% of Rs. In the Ra, fine roots with smaller radius (< 2 mm) has higher respiration. Previous studies indicated that the Moso bamboo invasion in East Asian have been important issue in recent year, which might change local carbon balance through the changes in soil carbon cycling. Previous study indicated that Rs and temperature sensitivity (Q10) of a Moso bamboo forest in the NTU forest were higher than those of other types of forests. The aim in this study is to estimate contribution of autotrophic respiration (Ra) to total Rs and to clarify mechanism of high temperature sensitivity of Rs in the Moso bamboo forest. To this aim, this study used trenching methods and core sample methods to separate Rh and Ra. As well, core sample methods enabled us to separate fine root (Rf) and coarse root (Rc) respiration from total Rs. Second, we used field experiments and lab experiments to estimate the Q10 in Rh, Ra, Rf, and Rc. Third, this study examined factors of the temperature sensitivity of the roots respiration using N concentration analysis. Forth, this study examined the definition of diameter based fine root using root orders, N concentration, and respiration rate In the Moso bamboo forest, this study conducted trenching methods to separate Ra from total Rs and also conducted core sample methods to separate Ra and Rh form Rs from March 2014 to February 2015, also separated the Rf, Rc, and rhizome respiration (Rr) from Ra. The core sample methods were also conducted in C. japonica forest which is near the Moso bamboo forest. Based on the field measurements, annual Q10 was determined for Rh, Ra, Rf, Rc and Rr. The roots samples collected by core sample were brought to the lab to quantify monthly Q10 of Rf, Rc and Rr with N analysis and dry weight measurements. The result showed Ra separated from trenching methods and core sample methods had almost same values with same seasonal variation patterns. The Ra accounted about 62 - 65% of the total Rs and the annual Ra was 507 - 587 g C m-2yr-1. The core sample methods indicated Rf had highest contribution to the Ra, and that the annual Rf, Rc and Rr was about 317 g C m-2yr-1, 184 g C m-2yr-1 and 54 g C m-2yr-1, respectively. Rf accounted about 55 % to toal Ra. Rf had the largest contribution of Ra in Moso bamboo. This study indicated annual Q10 of Ra (=3.61-3.92) was larger than that of Rh (2.45-2.84) in both trenching method and core sample method. In the core sample method, Rf in field measurement had higher Q10 value (4.95) than Rc (3.74) and Rr (0.19). Q10 of Ra in Moso bamboo forest was higher than that of C. japonica in both field measurements and incubation treatments. Besides, incubation experiment indicated Q10 of Rf had distinctive seasonal change with higher value in summer. The N analysis indicated that Rf had the highest N concentration than Rc and Rr, and that N concentration of Rf had distinctive seasonal change with higher value in summer. Thus, higher N concentration of Rf is related to high respiration and temperature sensitivity of Rf. Root respiration of Moso bamboo had distinctive change between order 2 and order 3 root. Diameter of order 2 was about 3.1 mm, what was similar with the definition in our study (2 mm). Thus the definition of Moso bamboo fine root in this study was probably valid. Overall, this study clarified Ra was an important part in Rs of the Moso bamboo forest compared with Rh, and fine roots were the main CO2 source in Ra with high Q10. Thus, this study indicated Ra and fine root may be the key of high Q10 of Rs in the Moso bamboo forest.

參考文獻


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