实验模拟氧化条件对微生物四醚脂的环境替代指标的影响  

EFFECTS OF OXIDATIVE DEGRADATION BY HYDROGEN PEROXIDE ON TETRAETHERS-BASED ORGANIC PROXIES

作　　者：丁伟华[1] 杨欢[1] 何钢强[1] 谢树成[1] 

机构地区：[1]中国地质大学(武汉)生物地质与环境地质国家重点实验室,武汉430074

出　　处：《第四纪研究》2013年第1期39-47,共9页Quaternary Sciences

基　　金：国家重点基础研究发展规划项目(973项目)(批准号:2011CB808800);国家自然科学基金项目(批准号:40930210和40921062);111项目(批准号:B08030)共同资助

摘　　要：以古菌和细菌细胞膜脂甘油四烷基甘油四醚(GDGTs)为基础建立的古温度指标四醚指数(TEX_(86))与甲基化/环化指标(MBT/CBT),以及陆源输入指标(BIT)与干旱和盐碱化指标R_(i/b),在海洋、湖泊、黄土-古土壤等沉积物的古环境重建中得到了广泛的应用。然而,利用这些微生物分子指标来重建古环境时,氧化等降解因素对GDGTs化合物,尤其是对细菌支链GDGTs的影响目前还不是很清楚。本研究通过过氧化氢模拟不同氧化程度对土壤中GDGTs化合物产生的影响,进而分析古菌和细菌GDGTs不同结构化合物抗氧化能力的差异,了解化学氧化降解对GDGTs各指标的影响。结果表明,古菌类异戊二烯GDGTs抗氧化能力低于细菌支链GDGTs,同时含环的古菌和细菌GDGTs抗化学氧化能力均要低于无环GDGTs。古菌GDGTs古温度指标TEX_(86)在氧化过程中逐渐降低,在氧化条件下沉积的古菌GDGTs的TEX_(86)指标用于古温度的重建存在低估的可能。在以无环细菌支链GDGTs为主的环境中,细菌MBT/CBT指标随氧化程度加深其重建温度基本不受影响。古菌与细菌GDGTs抗降解能力的差异导致陆源输入指标BIT指数随着氧化程度增加而升高,在地质体中应用此指标恢复古陆源输入存在高估的可能性。干旱化和盐碱化指标R_(i/b)随着氧化程度加深表现出逐渐降低的趋势,从而在应用上也可能存在低估。需要指出的是,实验室用的过氧化氢比自然条件下氧气的氧化作用强得多,本文的结论反映了一种比较极端的状况。The organic proxies such as TEX86 （the tetraether index of tetraethers consisting of 86 carbon atoms）, MBT/CBT（the methylation index/the cyclisation index）, BIT（the branched and isoprenoid tetraether index）and Ri/b（the ratio of isoprenoid GDGTs to branched GDGTs）based on the archaeal and bacterial glycerol dialkyl glycerol tetraethers （GDGTs）have been widely applied to reconstruct palaeoenvironment in marine, lacustrine sediments and loess-paleosol sequences. However, degradation like oxidation usually has a significant effect on GDGTs,which should be considered when these organic proxies, especially those branched GDGTs-based proxies, are used in palaeoenvironmental reconstruction. Therefore it＇s of great significance to evaluate the effects of oxidation on these proxies. Here ,we simulate the geological oxidation with hydrogen peroxide to investigate the changes of the different proxies. A soil sample with abundant GDGTs was collected from Chongqing（29°34.0＇N, 106°25.2＇E） where the soil profile is developed on an anticline formed by Permian and Triassic limestone. Sixty grams of soil sample were then separated into six aliquots equally. The samples were named as VSL-0-1, VSL-0-2, VSL-2, VSL-4, VSL-6 and VSL-8,which means they are oxidized for 0 hr,2 hrs,4 hrs,6 hrs and 8 hrs respectively. We then use hydrogen peroxide to oxidize soil powders and stirred samples by the magnetic mixer to homogenize the samples for the fixed time series at the room temperature. Once times up, we gathered the soil residuals with filters as soon as possible. The soil residuals were freeze-dried and ground into powders again. Finally,we extracted and detected GDGTs in the soil residuals to examine the changes of different proxies. The results showed that cyclopentane-containing GDGTs were less resistant to oxidation than acyclic GDGTs, and that the isoprenoid GDGTs are more easily degraded than the branched GDGTs in the oxidation experiment. The TEX86 index based on isoprenoid GDGTs is more easily to

关 键 词：过氧化氢 氧化GDGTs TEX86 MBT CBT BIT RI b古环境重建 

分 类 号：P593[天文地球—地球化学] Q949.3[天文地球—地质学]