台灣東部雷公火泥火山之微生物甲烷循環

Microbial methane cycling in the Lei-Gong-Huo mud volcano of eastern Taiwan.

張永欣(Yung-Hsin Chang)

指導教授 ： 林立虹

國立臺灣大學/理學院/地質科學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01336

摘要

泥火山與冷泉系統皆是重要的甲烷逸散的地質構造，來自深部熱裂解源及微生物所產生的碳氫化合物，藉由裂隙等通道釋放至大氣與海洋中。其微生物族群在陸域泥火山中所扮演的角色，有助於了解碳循環在不同深度儲庫間的調控。本研究目的在於探討台灣東部雷公火泥火山中的微生物甲烷循環，藉由分析噴發泥與距離噴發口不同距離的岩芯樣本 (岩芯 A 距離噴發口 0.34 m，岩芯 B 距離噴發口 1.53 m)，嘗試了解深部的流體通量如何影響微生物族群結構。
分析結果顯示此地區主要的微生物族群多為厭氧、耐鹽或嗜鹽特性菌種。靠近噴發口的環境以厭氧型甲烷氧化作用為主，其中岩芯 A 中深度5-9 cm 及 29 cm，為鐵－甲烷過渡帶，主要優勢古菌為 ANME-2a，其族群數量在不同深度樣本間的分布與 Dusulfuromonas/Pelobacter 族群為正相關，顯示金屬還原伴隨甲烷氧化作用發生的可能性。甲烷生成作用主要為利用甲基類代謝的甲烷菌種，並活躍於岩芯 A 深度9-27 cm 及岩芯 B 的淺部區間。細菌族群相較於古菌族群則有較高的物種豐富度及多樣性，其主要優勢菌種在岩芯 A 為 Desulfuromonas、Pelobacter、Marinobacter及未培養的 Bacteroidetes 相關菌種，岩芯 B 則轉換成以 Thiohalophilus 及未培養的 Bacteroidetes 相關菌種為優勢菌種。
綜合分子生物證據與地化資料，顯示深部富含碳氫化合物的流體湧升和來自大氣的氧氣，為調控泥火山中微生物族群結構變化與功能表現的重要因子。本地區泥火山的甲烷逸散，微生物的調控扮演重要的角色，在靠近噴發口的位置，甲烷經金屬還原伴隨甲烷氧化作用被大量消耗。距離噴發口較遠的位置，源自甲烷菌生成的甲烷則直接逸散至大氣。

關鍵字

泥火山 ； 微生物甲烷循環

並列摘要

Mud volcanoes and cold seeps are important geological features that facilitate the export of microbial and/or thermogenic hydrocarbons from deep sources to the overlying seawater and/or atmosphere. Understanding how microbial communities are regulated in terrestrial mud volcanoes would facilitate to unravel the carbon cycles linking deep and shallow reservoirs. The objective of this study was to characterize microbial communities associated with bubbling fluid and sediments along depth in two sites of the Lei-Gong-Huo mud volcano in eastern Taiwan. These sites were chosen (BF: bubbling fluid; site A: 0.34 meter from venting center; site B: 1.53 meter from venting center) in order to investigate how fluid flux would shape the community structures.
Site comparisons revealed that anaerobic, halophillic, salt-tolerated microorganisms were prevalent in both sites. Iron to methane transition occurred at depths of 5-9 cm and 29 cm in site A where archaeal populations were dominated by ANME-2a. The abundances of ANME-2a were positively correlated with those of Desulfomonas/Pelobacter sp., suggesting that anaerobic methanotrophy is coupled to the metal reduction. Methanogenesis primarily catalyzed by methylotrophic methanogens were actived at 9-27 cm depths of site A and shallow intervals of site B. Bacterial communities were highly diverse and composed of different assemblages. Dominant bacterial members switched from Desulfuromonas, Pelobacter, Marinobacter and uncultured Bacteroidetes-related microorganisms in site A to Thiohalophilus and uncultured Bacteroidetes-related microorganisms in site B.
The molecular evidence combined with geochemical characteristics revealed that the interplay between the upwelling, hydrocarbon-rich fluids, and downward atmospheric oxygen is essential to regulate community assemblages and functional expressions in mud volcanoes. Methane emission in the mud volcanoes was controlled by microbial processes. Near the venting site, methane is consumed by iron-dependent anaerobic oxidation of methane. Far from the venting site, methane produced from methanogen was directly realeased to atmosphere.

並列關鍵字

mud volcano ； microbial methane cycling

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