若干重大地質環境突變的地球生物學過程

謝樹成　王風平　顏佳新　儲雪蕾　史曉穎

摘 要：MCG古菌代表了一類自然界較古老的古菌，提議將MCG古菌歸類于一個全新的門類——深古菌門（Bathyarchaeota）。高濃度CO2造成的海水酸化對西太平洋海區浮游細菌的豐度、高DNA含量細菌、生產力等有促進作用，但對細菌的多樣性有一定程度的抑制作用。火山灰造成海洋異養細菌和真核自養生物的豐度均顯著升高，降低浮游病毒的豐度，導致微生物群落多樣性降低，使整個群落朝著不同方向演替。發現AOM細胞團在其表面形成粘土礦物，而在周圍環境中形成碳酸鹽，這可能與AOM反應產生的HS-增加環境堿度有關。西南印度洋深海微生物群落結構與鈣、磷、硫等元素具有相關性。提出了兩類示蹤古水文條件的微生物脂類指標、三類靈敏響應古溫度的微生物脂類指標。有機質-粘土礦物復合體能有效保護有機質遭受微生物的作用，對碳循環產生重要影響。不同微生物功能群的共存能促進粘土礦物結構鐵的還原，微生物成因的白云石主要與細胞表面的羧基官能團有關。發現古、中生代之交海洋環境具有高溫、缺氧、低硫酸鹽濃度、氮素匱乏的特征，生態系統不同營養層次的生物對海洋環境具有不同的響應能力，微生物對海洋水化學和全球變暖起重要作用。提出了兩幕生物危機與兩幕環境變化，溫度變化和缺氧環境可能導致了二疊紀-三疊紀之交的幕式生物危機。大滅絕后，在Griesbachian早期、Dienerian-Smithian之交、Smithian-Spathian之交出現嚴重的海洋缺氧、硫化事件，出現了微生物巖、鮞粒灰巖等異常沉積。 在雪球地球之前的拉伸紀古氣候已經開始不穩定。埃迪卡拉紀海洋的化學分層造成不同的生境及其不同的地球微生物學過程，造成DOC碳庫與DIC碳庫的分離，也造成不同于顯生宙的海洋碳循環。陡山沱組II和IV段在缺氧或硫化的水體中存在一個大DOC碳庫；陡山沱早期（II段）以光合自養微生物體系為主，到晚期（IV段）隨著透光帶硫化水體的發育，有大量化能異養微生物加入。晚埃迪卡拉紀-早寒武世海洋仍具有缺氧分層的高梯度狀態。早寒武世早期可能缺乏固氮作用相關，隨后趨于正常，氧化明顯并伴生多細胞生物發育。 華北中元古界發現大量微生物成因的凝塊石，在燕山盆地中元古代發現了兩個重要的生物群更替事件，分別與海洋化學變化以及火山活動導致的營養鹽輸入相關。發現了多種真核生物化石，表明這個時期真核生物已經出現明顯的多樣性分化。中元古代海洋DIC庫經歷了逐漸減小的演變，海洋硫酸鹽濃度較低，氧化還原界面較淺。在淺水環境自養微生物控制了碳的代謝過程，而深水環境厭氧微生物代謝對海水化學組成有很大影響。

關鍵詞：地質微生物功能群 全球變化 海洋水化學 極端環境 重大地質環境突變

Abstract： MCG is one of the earlier archaeal branches and taxonomically assigned to a new branch， Bathyarchaeota. CO2-induced oceanic acidification promotes the abundance of planktonic bacteria and the primary production but decreases bacterial diversity. Addition of volcanic ash induces the elevated abundance of heterotrophic bacteria and eukaryotic autotrophs， but decreases the abundance of planktonic viruses and microbial diversity. Microbial cells related to AOM lead to the precipitation of clay mineral on the cell surface but the carbonate in surrounding environments. Microbial lipid proxies were proposed to show sensitive responses to temperature and hydrological conditions. Organic-clay association could prevent organics from microbial degradation， which in turn impacts carbon cycle. Co-occurrence of microbial functional groups accelerates the reduction of iron within clay minerals. It is found that the ocean across the Permian-Triassic boundary is featured by hot， anoxic conditions with low concentration of sulfate and nitrate. Organisms of different trophic levels show varied responses to the deteriorative environmental conditions. Microbes play important roles in changing the oceanic chemistry and global warming at that time. Two episodes of faunal mass extinction and environmental crisis were proposed. Enhanced anoxia and euxinia were present in association with microbialites and giant oolites in early Griesbachian， Dienerian-Smithian transition and Smithian-Spathian. Oceanic stratification in Neoproterozoic results in the differentiation of bio-habitat and thus the different geomicrobiological processes， which in turn causes the separation of DOC pool and DIC pool and thus a carbon cycle different from that in Phanerozoic. Large DOC pool is present in association with anoxic or euxinic conditions during Doushantuo deposition. Photosynthetic autotrophs are dominant in Early Doushantuo but later replaced by chemoheterotrophs due to the expansion of euxinic zones. Thrombolites were demonstrated to be of microbial origin in Mesoproterozoic in North China craton. Two important replacements of microbes were found to relate to the change in oceanic chemistry and the enhanced input of nutrients resulted from volcanism， respectively. Eukaryote was documented to diversify at that period. Mesoproterozoic oceans are characterized by the decrease in DIC pool， the shallow chemocline and low concentration of sulfate.

Key Words： Geomicrobial functional group； Global change； Oceanic chemistry； Extreme environments

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