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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。
Based on the archaeal and bacterial cell membrane lipid glycerol tetraalkyl glycerol tetraether (GDGTs) based on the ancient temperature indicators of tetraether index (TEX_ (86)) and methylation / cyclization indicators (MBT / CBT), and terrestrial input Indicators (BITs) and drought and salinization indicators R_ (i / b) have been widely used in paleoenvironment reconstruction of sediments such as oceans, lakes and loess-paleosol. However, when using these molecular markers to reconstruct the paleoenvironment, the influence of oxidative degradation factors on the GDGTs compounds, especially the bacterial branched GDGTs, is not yet clear. In this study, hydrogen peroxide was used to simulate the effects of different oxidation levels on GDGTs compounds in soil. Then the differences of antioxidant capacity of different GDGTs compounds between archaea and bacteria were analyzed to understand the effects of chemical oxidation and degradation on GDGTs. The results showed that the anti-oxidative capacity of archaeal isoprene GDGTs was lower than that of bacterial branched-chain GDGTs, while both the archaea containing bacteria and GDGTs of bacteria had lower anti-oxidative abilities than GDGTs. The paleontal temperature indicator TEX_ (86) of archaea GDGTs decreased gradually during oxidation, and the TEX_ (86) indicator of archaeal GDGTs deposited under oxidative conditions was underestimated. The bacteria MBT / CBT index was largely unaffected by the deepening of the oxidation in the environment dominated by the uncyclic bacteria branched GDGTs. The difference of antidegradability of archaea and bacterial GDGTs led to the BIT index of terrestrial input index increasing with the increase of oxidation degree. It is possible to use this index to restore ancient terrigenous input in geological bodies. Aridification and salinization index R_ (i / b) with the deepening of the degree of oxidation showed a gradual downward trend, which may be underestimated in the application. It should be pointed out that the hydrogen peroxide used in the laboratory is much more oxidized than the oxygen under natural conditions and the conclusions of this paper reflect an extremely extreme situation.