张佳皓^1,2,,
黄钰莹^1,2,
王灿发¹,
杨欢^1,2,,
1. 生物地质与环境地质国家重点实验室, 中国地质大学(武汉), 湖北 武汉 430074
2. 中国地质大学(武汉)地理与信息工程学院, 湖北 武汉 430074

基金项目: 国家自然科学基金项目（批准号：41830319）资助


详细信息

作者简介: 张佳皓, 女, 26岁, 硕士研究生, 地质微生物研究, E-mail:cugzjh@163.com

通讯作者: 杨欢, E-mail:yhsailing@163.com

中图分类号: P593;P931.5

收稿日期:2020-01-18
修回日期:2020-03-26
刊出日期:2020-07-30

SOURCES OF GDGTS IN STALAGMITES FROM HESHANG CAVE,HUBEI PROVINCE IN CENTRAL CHINA:NEW EVIDENCE FROM 5,6-METHYL brGDGTS AND brGMGTS

Zhang Jiahao^1,2,,
Huang Yuying^1,2,
Wang Canfa¹,
Yang Huan^1,2,,
1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences(Wuhan), Wuhan 430074, Hubei
2. School of Geography and Information Engineering, China University of Geosciences(Wuhan), Wuhan 430074, Hubei


More Information

Corresponding author: Yang Huan,E-mail:yhsailing@163.com

MSC: P593;P931.5

--> Received Date: 18 January 2020
Revised Date: 26 March 2020
Publish Date: 30 July 2020


摘要
摘要:岩溶关键带是地球各圈层相互作用的场所，具有较为独特的生物地球化学过程。洞穴沉积物石笋是各圈层相互作用的产物，也是记录古气候的良好载体。目前，石笋中多种古气候代用指标已经被应用于古气候重建。来自于微生物细胞膜的甘油二烷基甘油四醚化合物（Glycerol Dialkyl Glycerol Tetraethers，即GDGTs）也在石笋中被发现，拓展了GDGTs相关指标的应用范围。然而，石笋GDGTs来源尚不明确，查明石笋中GDGTs来源是其相关指标得以准确应用的前提。本文以湖北清江和尚洞为例，对喀斯特洞穴关键带中古菌和细菌GDGTs的垂直分布进行了详细调查，发现表层土壤和洞穴内部石笋中GDGTs分布存在显著差异，土壤中细菌支链GDGTs（brGDGTs）显著多于古菌类异戊二烯GDGTs（isoGDGTs），而石笋与之相反。土壤中5-甲基brGDGTs多于6-甲基brGDGTs，而石笋中6-甲基brGDGTs为主要异构体类型，5-甲基brGDGTs几乎检测不到。包括5-和6-甲基brGDGTs的甲基化指数MBT、环化指数CBT和异构体指数IR在内的多种指标反映出的brGDGTs分布在土壤和石笋中均存在显著差异；此外，土壤中的甘油单烷基甘油四醚（GMGTs）相对含量远低于石笋中GMGTs的含量。洞穴滴水中GDGTs的检测也表明滴水GDGTs分布与洞顶土壤完全不同，其GDGTs组成以古菌isoGDGTs为主，且古菌isoGDGTs分布模式与石笋一致。这些证据都表明，石笋中GDGTs化合物不是来自于洞穴上层土壤；石笋中的GDGTs可能主要来自于石笋表面原位生长的菌群和岩溶裂隙中地下水系统的贡献，其记录的信号主要是地下水和洞穴内部的环境信息，而非土壤的环境信息。
关键词: 石笋/
古菌isoGDGTs/
细菌brGDGTs/
来源/
地下水/
土壤

Abstract:Stalagmite is an important archive for the paleoclimate research. A number of proxies have been used in stalagmites to reconstruct the paleoenvironment. Among these proxies, glycerol dialkyl glycerol tetraethers (GDGTs) derived from microbial cell membrane have emerged as a promising tool to reconstruct paleoclimate in stalagmites. However, the sources of GDGTs in stalagmites is still unclear, hindering their wide application.
In order to determine the source (s) of GDGTs in stalagmite, we investigated the distribution of isoGDGTs and brGDGTs in the karst critical zone over Heshang Cave in Qingjiang valley of Hubei Province, central China (30°27'N, 110°25'E; 530 m above sea level). This region is subject to a typical subtropical monsoon climate, and precipitation mainly falls in the summer. The mean annual precipitation is about 1400 mm and the mean annual temperature is 16~17℃. We collected 20 surface soils (sample No. LBT-X, X denotes its number), a soil profile (sample No. LBT-P-X; a total of 14 samples for all depths) with a depth of 70 cm, 18 dripping water samples spanning from February 2019 to September 2019 (labeled as HS4D-X and HS6D-X) and a stalagmite (labeled as HS4-X). GDGTs in above samples were extracted with organic solvents and analyzed using an Agilent liquid chromatography mass spectrometry (HPLC-MS). The distribution and concentrations of archaeal isoprenoid and bacterial branched GDGTs (isoGDGTs and brGDGTs) were obtained. The sources of GDGTs in Heshang cave stalagmite was then examined by means of comparison of the distributions between soils, stalagmites and dripping water.
Distribution of GDGTs in surface soils and the soil profile differed markedly from that in the stalagmite. Specifically, brGDGTs dominated isoGDGTs in soils whereas the stalagmite showed the opposite. The relative abundance of brGDGTs vs. isoGDGTs, which can be reflected by BIT index, varied from 0.04~0.51 in stalagmites, much smaller than that (ca. 1) in the soils. BrGDGTs were dominated by brGDGT-Ia in soils, in contrast to the dominance of Ⅱ a' in stalagmites. The most abundant compound of isoGDGTs in soils was crenarchaeol and, in some cases, was GDGT-0. However, crenarchaeol was found to be most abundant in all stalagmite samples.
In addition, 5-methyl brGDGTs were found to be more abundant than their 6-methyl isomers in the overlying soils, while 5-methyl brGDGTs in the stalagmite samples were extremely low in abundance. The IR index, expressing the relative abundance of 6-vs. 5-methyl brGDGTs, ranged from 0 to 0.88 in soils, whereas this index was close to 1 in most stalagmite samples. Cross plots of the methylation index (MBT) and the cyclisation index (CBT) exhibited significant difference between stalagmite and soils. GMGTs have been identified in the stalagmite samples, in contrast to the near absence of them from the surface soils and soil profile.
GDGTs in the suspended particulate matter (SPM) of dripping water also provides clues to the provenance of GDGTs in stalagmites. GDGTs in SPM samples were composed of archaeal isoGDGTs dominated by crenarchaeol and followed by GDGT-0 and GDGT-1. The distribution of GDGTs in the SPM samples were different from that in the surface soils and the soil profile but were similar to that in the stalagmite.
To sum up, the above comparisons provide several lines of evidence for the origin of GDGTs in stalagmites from the underground water (dripping water) or cave system rather than from the soils over the cave.
Key words:stalagmite/
isoGDGTs/
brGDGTs/
source/
groundwater/
soil



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