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人工无本底土壤培养实验下GDGTs的含量与分布特征

Abundance and Distribution of GDGTs in Incubated Artificial Soils with no Fossil Pool

  • 摘要: 微生物来源的甘油二烷基甘油四醚类化合物(GDGTs)是古气候变化研究的重要工具。培养实验有助于明确GDGTs对环境参数的响应机理,检验相关气候代用指标的可靠性。然而目前的GDGTs培养实验主要针对单一菌株或存在本底信号影响,制约了对土壤环境中GDGTs对环境因子精确响应的系统理解。本文利用人工配置的无GDGTs土壤进行了4年相同温度不同土壤含水量(SWC)条件下(0~10%、0~20%、0~30%、0~40%)的实验室培养,以探究无本底培养实验获得的GDGTs的含量与分布特征及其对培养条件的响应。结果表明:①GDGTs含量与SWC正相关,但添加磷酸盐缓冲溶液会抑制GDGTs的产生;②基于野外调查提出的能反映土壤湿度变化的支链与类异戊二烯四醚(BIT)指标与SWC无明显相关性,因而土壤中BIT指标可能间接而非直接响应SWC变化;③本实验条件下6-甲基支链GDGTs(brGDGTs)较5-甲基brGDGTs占绝对主导,导致古温度指标MBT'5ME值极高而MBT'值极低,从培养实验角度证实较高的6-甲基brGDGTs 相对含量会影响brGDGTs古温度指标的准确性。

     

    Abstract: Glycerol dialkyl glycerol tetraethers (GDGTs) derived from microorganisms are important tools for the study of paloclimate changes. Incubation experiments are helpful to clarify the mechanisms for the responses of GDGTs to environmental parameters, and to test the reliability of related climatic proxies. However, previous GDGT incubation experiments were mainly conducted on a single strain or suffered from the influence of background signal, hampering systematically understanding the precise response of this biomarker to environmental factors in soil environment. In this study, artificial soils without GDGTs were incubated under the same temperature but different soil water content (SWC) conditions. The results showed that: (1) the abundances of GDGTs were positively correlated with SWC, but phosphate buffer could inhibit the production of GDGTs; (2) The branched and isoprenoid tetraether index (BIT), a soil moisture proxy developed in natural soils, was not significantly correlated with SWC; (3) 6-methyl brGDGTs were more abundant than 5-methyl brGDGTs, resulting in extremely high values of MBT'5ME and low MBT'. Our results suggest that the BIT soil moisture proxy may indirectly (rather than directly) respond to SWC changes, and confirm that high relative abundance of 6-methyl brGDGTs can affect the applicability of the MBT'5ME paleothermometer in soils. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202405240120.

     

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