湿地沉积微生物藿类对干旱的响应机制及其古气候意义

It is a very important scientific issue to explore the response of wetland microbial processes to extreme climate under the background of frequent global extreme climate. In the early time, we identified several drought stages in the middle Holocene in Dajiuhu wetland. During these drought stages, the contents and isotope values of microbial hopanoids changed differently suggested that these hopanoid-produced microorganisms may come from different microbial processes. But the mechanism of these microbial hopanoids response to drought is still unclear which limits the interpretation of paleoenvironment. This project carries out continuous monitoring process in the field and cultures the moss and surface peat with different temperatures and water levels in the laboratory to find out the environmental factors controlled the distribution of microbial hopanoids. Combined with 13CH4 isotope labeling experiment, the response mechanism of these hopanoid-produced microorganism processes especially the methane oxidation process to drought is analyzed. In addition, a comparative analysis is conducted in the sedimentary core at the dry sedimentary edge and the wet sedimentary center of the Dajiuhu wetland to explore the diagenetic transformation process of microbial hopanoids and to establish indicators based on microbial hopanoids to reflect extreme drought events in the paleoclimate record.

在全球极端气候频发的背景下探讨湿地微生物过程对极端气候的响应是一个非常重要的科学问题。我们前期在大九湖湿地沉积钻孔识别出中全新世的几个干旱阶段，在这些干旱阶段微生物藿类化合物含量和同位素变化不一致，说明这些微生物藿类可能来自不同的微生物过程。目前湿地这些微生物藿类对极端干旱的响应机制尚不清楚，限制了基于微生物藿类化合物古环境重建的解译。本项目以神农架大九湖湿地为研究载体，在野外开展连续的现代过程监测，同时在实验室进行单一环境因子的培养实验，查明湿地微生物藿类分布的环境受控因素。结合13CH4同位素标记实验剖析这些产藿类微生物过程特别是甲烷氧化过程对干旱的响应机制。另外对大九湖湿地沉积边缘较干处和沉积中心较湿处的沉积柱进行对比分析，探讨湿地钻孔中微生物藿类化合物的成岩转化过程，建立基于微生物藿类的指标用于反映古气候记录中的极端干旱事件。

极端干旱事件频繁发生对泥炭地的生态稳定性产生较大的影响。本项目以神农架大九湖泥炭地为研究载体，在野外开展连续的环境因子、泥炭化学参数、表层泥炭及植物的脂类监测，探讨环境因子对湿地微生物脂类的影响，以及湿地微生物脂类对泥炭地的反馈。同时在实验室开展泥炭和泥炭藓单一环境因子调控揭示泥炭微生物群落应对环境变化的策略。主要取得以下重要进展：1，对大九湖泥炭地主要成碳植物（地榆、乳浆大戟和苔草）叶蜡正构烷烃氢同位素季节性监测发现泥炭沉积叶蜡氢同位素记录了叶片生长末期（稳定期）的环境信号；2，湿地水文变化驱动微生物群落、碳代谢活动和温室气体通量快速变化。微生物藿类及磷脂脂肪酸同位素特征指示了水位下降（干旱时期）微生物甲烷氧化活动的增强。3，建立正构烷烃、烯烃及藿类分离方法并准确测试连续监测表层泥炭脂类同位素。分析了不同生境下苔藓植物中脂类（正构烷烃和里白烯）及其碳同位素探讨了陆生附生苔藓植物中里白烯的生物来源。本项目的研究为极端环境事件发生过程中微生物演化过程及泥炭地碳循环过程提供了重要的理论依据。