有机质-铁-硫氧化还原耦合作用下控制泥炭沼泽土壤厌氧呼吸过程的关键机制研究

The relevance of biogeochemical gradients for turnover of organic matter and contaminants is yet poorly understood. This study aims at the identification and quantification of the interaction of different redox processes along gradients. The interaction of iron-, and sulfate reduction and methanogenesis will be studied in controlled batch and column experiments. Factors constraining the accessibility and the energy yield from the use of these electron acceptors will be evaluated, such as passivation of iron oxides, re-oxidation of hydrogen sulfide on iron oxides. The impact of these constraints on the competitiveness of the particular process will then be described. Special focus will be put on the evolution of methanogenic conditions in systems formerly characterized by iron and sulfate reducing condition. As methanogenic conditions mostly evolve from micro-niches, methods to study the existence, evolution and stability of such micro-niches will be established. To this end, a combination of Gibbs’ free energy calculations, isotope fractionation and tracer measurements, and mass balances of metabolic intermediates (small pool sizes) and end products (large pool sizes) will be used. Measurements of these parameters on different scales using microelectrodes (mm scale), micro sampling devices for solutes and gases (cm scale) and mass flow balancing (column/reactor scale) will be compared to characterize unit volumes for organic matter degradation pathways and electron flow. Of particular interest will be the impact of redox active humic substances on the competitiveness of involved terminal electron accepting processes, either acting as electron shuttles or directly providing electron accepting capacity. This will be studied using fluorescence spectroscopy and parallel factor analysis (PARAFAC) of the gained spectra. We expect that the results will provide a basis for improving reactive transport models of anaerobic processes in aquifers and sediments.

泥炭沼泽是陆地生态系统中重要的碳库，探求控制泥炭沼泽土厌氧呼吸的关键因素对核算其碳排放量意义重大。泥炭沼泽土厌氧呼吸过程中不同电子受体交互作用机制复杂，研究选取淹水-落干关键带泥炭沼泽土为研究对象，模拟淹水环境下有机质、铁、硫氧化还原过程交互机制，通过湿式化学实验、室内培养实验等，借助创新有机质氧化还原能力电化学分析技术、稳定同位素技术、同步辐射痕量分析技术等先进研究技术和方法，定性、定量分析有机质-铁-硫耦合作用过程，包括：动力学过程、氧化还原中间和终端产物、电子流平衡状况以及相应的吉布斯自由能变，研究拟从分子水平和热力学角度揭示有机质-铁-硫氧化还原交互机制，厘清控制泥炭沼泽土壤厌氧呼吸过程的关键控制因子，实现定量评估不同电子受体交互、竞争过程对温室气体排放的影响。最终，将实验获得的关键因子以及相应参数纳入碳排放模型，为修正我国湿地碳排放量核算提供理论支撑。

泥炭沼泽是陆地生态系统中重要的碳库，是全球变化研究的热点地区，探求控制泥炭沼泽土厌氧呼吸的关键因素对核算其碳排放量意义重大。大气干湿沉降为泥炭湿地输入大量无机盐离子，土壤厌氧呼吸过程中不同电子受体交互作用机制复杂。本项目按照项目书的要求及年度计划，已基本完成既定研究任务。通过野外原位泥炭剖面分析和室内培养实验，联合分析了淹水环境下有机质、铁、硫氧化还原过程交互机制及影响因子，评估了不同电子受体交互、竞争过程对温室气体排放的影响，提出了硫酸根和腐殖质等电子受体会提高溶解有机物的浓度，而溶解有机物作为微生物呼吸利用底物进而削弱对甲烷的抑制作用，同时有机底物含量可显著影响泥炭的碳矿化和温室气体的排放；外源铁输入可促进富含有机质泥炭土壤的甲烷排放，且甲烷生成取决于铁碳结合物的稳定性，其受厌氧条件下三价铁还原的影响。研究结果揭示了铁、硫与天然有机质氧化还原交互机制，分析了控制泥炭沼泽土壤厌氧呼吸过程的关键控制因子，对了解天然环境下泥炭沼泽湿地生态系统与大气系统之间的温室气体排放、碳交换过程有指示作用。.截止到2022年底，已发表学术论文11篇，其中SCI论文5篇，中文核心期刊论文6篇；申请了国家专利3项，其中3项已获得授权；培养了9名在读硕士研究生，项目执行期间项目组成员参加国内外学术交流会议5次，超过了项目书的既定目标。.本项目研究结论对于深入认识碳储备量最高的泥炭沼泽甲烷、二氧化碳排放规律和重要影响因素具有主要意义，可精确定量评价湿地在碳排放中的真实贡献提供理论支撑。建议未来可进一步改进方法并结合微生物过程拓展到湖泊等淡水湿地，并结合碳排放模型，为修正我国湿地碳排放量核算提供理论支撑。