东北全新世泥炭微生物类脂物记录:季风变化及其对甲烷生物地球化学过程的影响

It is crucial to understand terrestrial microbial processes because they governgreenhouse gas emissions; unfortunately, the long-term microbial responses to climate change remain unclear, causing uncertainty in predictions for how they will impact future climate and atmospheric composition. The peatland from the Northeast China, controlled by the East Asian Monsoon system, has been major players in climate change and carbon cycling, such that these deposits represent a truly novel potential to address the above scientific issues. This proposed research will expand the Northeast China dataset of peat-forming plant δ D values, a key hydrological indicator; quantify and isotopically characterise microbial biomarkers and especially those derived from organisms involved with methane cycling; evaluate the link between precipitation, vegetation, redox conditions and microbially mediated processes and especially methanogenesis. These records will be developed using cutting edge approaches exploiting gas chromatography (GC), GC-mass spectrometry, high performance liquid chromatography-mass spectrometry, GC-isotope ratio mass spectrometry (IRMS) and GC-thermal conversion-IRMS. This dataset seeks to understand methanogenic and methanotrophic processes and will be used to develop higher resolution and longer-term CH4 biogeochemical records over the Holocene and to better understand the impact of the East Asian monsoon change on modern and ancient CH4 biogeochemistry, to ultimately embed them in the framework of known and hypothesised relationships between microorganisms and climate change， and to explore how CH4 biogeochemical processes will respond to monsoon climate change and whether this will act as a positive, negative or netutral feedback on monsoon climate change. This work will be one of the very first applications of these novel methodologies to the study of past changes in peat biogeochemistry in Northeast China. It will validate and expand on the Chinese investigations and contribute to a better mechanistic understanding of the microbial response to climate change and its impact on CH4 biogeochemistry.

陆地微生物过程控制着温室气体释放，关系到气候变化长期响应等科学问题，成为预测未来气候及大气组成方面的瓶颈。受控于东亚季风的我国东北泥炭地在气候变化与碳循环中占有重要地位，是解决上述科学问题的最佳突破口。本项目应用分子有机地球化学方法高分辨率地建立植物叶腊单体氢同位素（δD）季风降水指标，定量研究微生物类脂物及其藿类碳同位素组成与特征，评价降水、植被、氧化还原条件及微生物过程之间的联系，发展高分辨率、长序列的甲烷生物地球化学分子记录。着力探索产甲烷与甲烷氧化过程，示踪泥炭地全新世甲烷生物地球化学循环，深入揭示东亚季风变化对现代与全新世甲烷生物地球化学过程的影响，并将其置入微生物与气候变化关系的框架中，探索全新世甲烷生物地球化学过程如何响应季风变化。本项目将是率先应用这些国际前沿方法研究东北泥炭生物地球化学过程，从根本上了解微生物对气候变化的响应，深化甲烷生物地球化学与季风气候的机制研究。

本项目在AMS 14C可靠年代标尺的基础上，运用GC-MS,HPLC-MS等对我国东北泥炭微生物类脂物记录进行了高分辨率研究，定量重建了该区16ky以来的年均温度(MAATpeat)变化序列，揭示了全新世以来有水文演化及控制因素，建立了其微生物群落与过程的类脂物代用记录。研究显示，东北地区末次冰消期期间温度变化幅度（可达约10°C以上）远大于中低纬度和同纬度的亚洲季风区，这种大幅度的变化表明东北地区与北半球高纬气候密切相关，提出在末次冰期，与极地海冰扩张和北大西洋温盐环流减弱有关的高纬地区的变冷，使中纬度西风环流与西北风增强，并传输更多冷空气到东北地区。在末次冰消期期间西风环流及其冷空气的传输减弱，放大了该区域的变暖，认为北大西洋气候对我国东北地区较其他亚洲季风区影响显著。自早全新世以来，整个东北地区有效湿度持续增加，以暖干-冷湿气候变化模式为主，这一现象与中亚干旱区一致，但显著不同于其它东亚季风区。因此，我们提出除了东亚季风影响我国东北地区外，中纬度西风环流也对该区具有重要的控制作用。在这样多大气环流影响的气候背景下，古菌与细菌膜类脂物记录显示较强的产甲烷过程与甲烷氧化过程均发生在早全新世，在温度较低的中晚全新世时期产甲烷过程和甲烷氧化过程减弱。该成果不仅对中国大陆不同区域突变事件及降水趋势与水资源分布等具有十分重要的指导意义，而且对东北泥炭对于全新世期间季风和西风环流驱动的水文和温度变化如何影响甲烷释放提供了科学证据。