【作者】 杨欢；

【导师】 谢树成；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2010， 硕士

【摘要】 类脂物作为生物标志化合物,其结构和组成的改变能够记录环境的变化,已经被广泛应用于多种沉积载体古环境的重建中。然而,根据“将今论古”的原理,类脂物的环境指示意义必须在现代过程中证实才能应用于恢复古环境变化。现代过程中类脂物对环境温度和降雨等响应的研究是类脂物应用于古环境重建的前提和基础。植物只能在较大时间尺度上才能响应环境的变化,而微生物类脂物的结构和组成变化能够迅速灵敏地记录下生存环境温度等的变化,在第四纪古环境研究中越来越显示出其重要的地位。土壤作为全球变化研究中的一个焦点,其微生物类脂物丰富,容易采集,且在不同气候带分布广泛,是研究现代过程中微生物类脂物对环境温度、降雨等响应的理想材料。本文选取了海南尖峰岭不同海拔表层土壤和中国不同气候带土壤对其中的微生物类脂物进行研究。不同海拔带来的温度差异和不同气候带的温度和降雨量差异为检验和建立基于微生物类脂物的有机地球化学指标提供了良好的条件。通过气相色谱-质谱仪与液相色谱-质谱仪检测了包括脂肪酸、脂肪醇、古细菌膜脂甘油四烷基链甘油四醚化合物(GDGTs),细菌支链GDGTs在内的多种微生物标志物,并尝试以这些微生物类脂物为基础建立新的古温度计。同时,对中国不同气候带表层土壤中的细菌支链GDGTs进行调查,查明了其分布的环境控制因素,建立适合中国区域范围内的古温度指标MBT/CBT指数的校正公式,并探索陆源输入指标BIT指数的环境影响因素。此外,还利用过氧化氢氧化土壤中GDGTs化合物,以模拟地质体中氧化条件下TEX86、MBT/CBT指数、BIT指数等所受的影响,为准确恢复古环境变化提供依据。上述的研究主要得到以下几点认识：1)尖峰岭不同海拔表层土壤中存在(反)异构脂肪酸,(反)异构脂肪醇、不饱和脂肪醇、3-羟基脂肪酸、2-羟基脂肪酸、古菌GDGTs与支链GDGTs等微生物标志物。土壤中微生物(反)异构脂肪醇是以蜡脂形式存在的,只有经过皂化才能释放出支链脂肪醇。在纯培养的革兰氏阳性菌和海洋好氧不产氧光合细菌中发现了含量明显的异构脂肪醇,为异构脂肪醇来源于微生物提供了直接证据。通过尖峰岭土壤微生物类脂物,建立了反异构十五酸/异构十五酸、反异构十五醇/异构十五醇、反异构十五醇/正构十五醇、不饱和十八醇/饱和十八醇四种新的古温度指标。反异构十五醇/异构十五醇比值、反异构十五醇/正构十五醇比值、不饱和十八醇/饱和十八醇比值均与海拔之间呈负相关关系,而反异构十五酸/异构十五酸比值却随海拔升高而逐渐增大。这其中,反异构十五醇/正构十五醇比值与由海拔换算成的年平均温度MAT、土壤pH的线性关系最为显著,其校正公式为α15/n-15=0.114*pH+0.0234*MAT-0.773(R2=0.80)。微生物脂肪酸和脂肪醇与海拔之间的相关关系,是微生物细胞膜适应温度变化的结果。此外,古细菌GDGTs与细菌支链GDGTs化合物均能够响应不同海拔温度变化,在陆地古环境重建中有较好的应用前景。2)细菌支链GDGTs与古细菌类异戊二烯GDGTs广泛存在于中国不同气候带土壤中,其相对含量变化主要受土壤pH控制。土壤pH在8.0以下时,细菌支链GDGTs较古菌GDGTs含量高；而在pH大于8.0的盐碱化土壤中,古细菌GDGTs一般比支链GDGTs丰度高很多。这些说明泉古菌更适合于盐碱化土壤中生存,而合成支链GDGTs的细菌则更适应酸性环境。古细菌GDGTs中无环的GDGTV (Cald)大部分来源于广古菌门,包括产甲烷古菌和嗜盐古菌等,而泉古菌醇GDGTⅣ与IV’(Cren)则主要来源于营氨氧化功能的泉古菌。基于此构建的古菌群落指数ACI= Cald/(Cald+Cren)表现出与土壤pH的相关性。ACI指数随土壤pH的变化呈现倒抛物线趋势,即随土壤pH增大,ACI值先变小再变大。ACI值的变化指示的是土壤中古菌群落的变化,即土壤pH在6.0～8.0之间时,泉古菌占主导地位；而当pH大于8并继续增大时,ACI值也逐渐增大,土壤中嗜盐古菌的丰度逐渐增加；在酸性环境中,泉古菌不太适合生存,因此酸性土壤中广古菌的相对含量有所增加。3)中国土壤支链GDGTs的甲基化指数MBT与环化指数CBT具有很好的环境指示意义。中国土壤中支链GDGTs的MBT与年平均降雨量或土壤pH的相关性高于年平均温度MAT,而在全球校正中MBT却主要与MAT相关,证明了全球校正在中国区域条件下会产生较大偏差；而环化指数CBT与土壤pH有很好的负相关关系,与全球校正一致。综合上述关系,建立了中国区域内陆地古温度重建校正公式MBT=-0.02+0.21*CBT+0.03*MAT(R2=0.83)和古降雨量重建公式MBT=0.134+0.109*CBT+0.000318*MAP(R2=0.86),提高了支链GDGTs应用于中国区域古环境重建中的准确性。4)陆源输入指数BIT值受土壤pH影响显著。土壤pH值增大时,其BIT值减小。pH大于6.0的土壤其BIT值大多小于1,这明显动摇了海洋沉积物BIT值正确估算陆源输入的前提,即BIT值必须接近于1。因此,在利用海洋沉积物BIT值估算陆源输入时,必须考虑陆源土壤的pH,以陆源土壤BIT值为基础,才能避免陆源输入的低估。5)随氧化程度加强,土壤TEX86逐渐减小,而CBT值却逐渐增大,说明含环的GDGTs较无环的GDGTs更容易被氧化。支链GDGTs甲基化指数MBT在氧化实验中保持稳定,古温度指标MBT/CBT受氧化影响很小。陆源输入指标BIT随氧化加强逐渐变大,表明支链GDGTs较古细菌GDGTs更抗氧化。因此,存在有机质氧化等降解过程的沉积物中使用BIT值容易造成高估。氧化实验的结果将对古环境重建中准确评估基于GDGTs所建立的指标受氧化等影响造成的偏差提供依据。更多还原

【Abstract】 Lipids as biomarkers can record environmental change on basis of variations of their structures and compositions, and therefore have been widely applied to reconstruct paleoenvironment in diverse geologic settings. However, the present is the key to the past. The feasibility of proxies for paleoenvironment should be validated in the modern processes prior to their use in paleoenvironment interpretation. The study on the response of lipids to environmental temperatures and precipitation can provide the prerequisite and basis for application of lipids on paleoenvironment reconstruction. Plants can only respond to the environmental change at a large time scale while the structures and compositions of microbial lipids can sensitively track the ambient environmental change such as temperatures etc., thus playing a more and more important role in the Quarternary paleoenvironment research. Soils, as a focus of global change research, are the ideal materials for studying the response of microbial lipids to environments because soils are rich in microbial lipids, readily collected and widely distributed in different climate zones.This dissertation will focus on microbial lipids in the surface soils across an alitude transect of Mt. Jianfengling and from different climate zones of China. The temperature and precipitation difference as a result of altitudes and climate zones can provide favorable conditions for validating and establishing novel organic geochemical proxies in terms of microbial lipids. So many kinds of microbial lipids including fatty acids, fatty alcohols and archaeal or bacterial glycerol dialkyl glycerol tetraethers (GDGTs) have been detected by gas chromatogram and mass spectrometry as well as liquid chromatogram and tandem mass spectrometry, and also used to establish new paleothermometers. The factors controlling branched GDGTs distribution in surface soils from different climate zones of China have been investigated and the equation for MBT/CBT index has been calibrated to cater for its use in Chinese regional environment. Besides, the environmental factors influencing the terrestrial input index, BIT has also been determined. We also simulate the impact of oxidation on paleoenvironmental proxies including TEX86, MBT/CBT and BIT index by hydrogen peroxide, which may provide the basis for accurate paleoenvironmental interpretation. Integrated with progress in above research, conclusions were drawn as follows.1) The microbes in the surface soils of Mt. Jianfengling can produce diverse biomarkers including (anteiso) iso fatty acids,(anteiso) iso fatty alcohols, unsaturated fatty alcohols, 3-hydroxy fatty acids,2-hydroxy fatty acids, archaeal and bacterial GDGTs. The branched fatty alcohols in the soils occur as wax and can only be released by saponification. The iso fatty alcohols have been found in pure-cultured gram-positive bacterium and AAPB, thus providing direct evidence for the sources of branched fatty alcohols. Four novel paleothermometers including the ratios of a15/i15 (acids), a15/i15 (alcohols), a 15/n-15(alcohols) and unsatured/saturated octadecanol were established based on microbial lipids in the soils of Mt. Jianfengling, where the ratios of a15/i15 (alcohols), a 15/n-15(alcohols) and unsaturated/saturated octadecanol correlate negatively with altitudes while the ratio of a15/i15 (acids) increase with increasing altitudes. The most significant correlation exists between the ratio of a15/n-15(alcohols), altitudes-derived mean annual temperature (MAT) and soil pH, yielding a calibration equation a15/n-15= 0.114*pH+ 0.0234* MAT-0.773 (R2=0.80). The response of microbial fatty acids and alcohols to the altitude in fact results from the adaptation of microbial membrane to ambient temperature. Moreover, archaeal and bacterial GDGTs both show great potential in reconstructing terrestrial paleoenvironment due to their response to temperature change in Mt. Jianfengling.2) The microbial branched GDGTs and archaeal GDGTs are widely distributed in soils from different climate zones of China and their relative abundance are primarily controlled by soil pH. The microbial branched GDGTs have higher abundance than archaeal GDGTs when soil pH is below 8.0, while in the alkaline soils with pH higher than 8.0 the achaeal GDGTs markedly exceed in abundance over bacterial GDGTs. Archaeal GDGT V without rings are known to primarily come from Euryarchaeota including methanogens and halophilic archaea whereas crenarchaeol are mainly derived from ammonia-oxidizing Crenarchaeota. On this point, archaeal commomunity index (ACI) was defined to describe the relative abundance of Euryarchaeota and Crenarchaeota. The ACI shows a close relationship with soil pH, i.e. the ACI values decrease with higher soil pH first and then increase when soil pH is higher than 8.0. The ACI shows that the Crenarchaeota dominate when soil pH is between 6.0 and 8.0 while the abundance of halophilic archaea increase when soil pH is higher than 8.0. The reliance of ACI on soil pH indicates that the most suitable environment for ammonia-oxidizing Crenarchaeota to flourish may have pH between 6.0 and 8.0.3) The MBT and CBT index of branched GDGTs in Chinese soils show good environmental significance. The correlation coefficient between MBT in Chinese soils and mean annual precipitation (MAP) or soil pH is much higher than MBT vs. MAT while in global calibration MBT is closely related to MAT rather than MAP, indicating that global calibration for MBT and MAT does not fit for the paleoenvironment reconstruction in Chinese geologic settings. However, CBT index in Chinese soils also shows good negative correlation with soil pH, in consistent with its global calibration. Integrated with above relations, two new calibrations for paleotemperature and paleoprecipitation reconstruction in China were established, i.e. MBT=-0.02+0.21*CBT+ 0.03* MAT (R2=0.83) and MBT=0.134+0.109*CBT+0.000318*MAP (R2=0.86), which improved the accuracy in Chinese regional paleoenvironment reconstruction.4) The terrestrial input index, BIT is remarkably influenced by pH of Chinese soils. The BIT values decrease with higher soil pH. Most BIT values in the soils with pH higher than 6.0 are lower than 1, which can not fit for the prerequisite to accurately and correctly estimate the terrestrial input, i.e. the BIT values of soils should approximate to 1. Therefore, soil pH in the river drainage basin should be considered before terrestrial input estimation via BIT index. If the BIT values of soils are much lower than 1.0, terrestrial input estimation should be based on BIT values of soils to avoid underestimate.5) The TEX86 values decrease while CBT values increase with increasing oxidation of GDGTs in soils, suggesting that ring-bearing GDGTs are more readily degraded than GDGTs without rings. The MBT of branched GDGTs in soils keep constant throughout the oxidation experiment, leading to neglectable change in MBT/CBT-derived temperatures. The BIT values increase with enhanced oxidation, implying that branched GDGTs are more resistant to oxidation than archaeal GDGTs. Therefore, the oxidation of GDGTs in sediments may result in overestimate of terrestrial input via BIT index. The results in the oxidation simulation experiments will provide basis for accurately reconstructing paleoenvironment based on TEX86, MBT/CBT and BIT.更多还原