湿地天然有机质和内部硫循环影响甲烷排放的微观机制

Peatlands store globally significant amounts of carbon and are important sources of the greenhouse gas methane to the atmosphere. However, for reasons which are not well understood, many peatland soils produce smaller amounts of methane than theoretically predicted. The relevance of biogeochemical gradients for turnover of organic matter and internal sulfur cycling is yet poorly understood. To identify constraints on anaerobic peat decomposition, ombrotrophic peat soil virtually devoid of inorganic electron acceptors was selected and we conduct both abiotic/biotic incubation experiments and field work to identification and quantification of the interaction of organic matter and internal sulfur cycling for suppressing methane production. The interactions between sulfide, sulfate reduction, methanogenesis, and organic matter redox processes are investigated by using novel electrochemical method to evaluate redox properties of organic matter, carbon/sulfur stable isotope technic to analysis their transformation pathway and sulfur K-edge X-ray absorption near edge structure to characterize the fate and transformation of newly formed organic sulfur in organic matter. These results demonstrate that both organic matter and internal sulfur cycling are key component of anaerobic decomposition in peatlands, and is at least partially responsible for their low methane production. Thus, organic matter and internal sulfur cycling may be a key regulator of how peatlands respond to ongoing global change. The results will improve a process-based model for assessing the methane budgets of global terrestrial ecosystems and evaluation of uncertainty.

湿地生态系统是重要的碳库，也是大气中甲烷的主要来源。前期研究发现部分湿地排放的甲烷量远低于理论预期值，因此，探求湿地土壤厌氧呼吸过程中影响甲烷排放的关键机制对正确估算甲烷排放通量至关重要。研究选取无机电子受体含量较低的雨养湿地为研究对象，通过室内微宇宙实验、样地微尺度原位试验，借助有机质氧化还原能力电化学分析技术、碳和硫的稳定同位素技术、硫的同步辐射检测技术等先进手段，探讨湿地有机质和内部硫循环参与并影响土壤厌氧呼吸的机制问题。从分子水平揭示淹水环境下天然有机质和硫酸盐再循环过程的交互机制，厘清天然有机质和硫循环交互过程对湿地土壤厌氧呼吸甲烷排放的关键影响机制。解析湿地生态系统温室气体排放规律，确定影响其排放的关键因子，参数化室内和样地试验结果，为湿地碳排放预测模型关键参数的确定提供必要的参考，最终为评价湿地在碳排放中的真实贡献提供理论支撑。

泥炭地是目前全球变化研究的热点区域，其拥有大量有机碳，是全球重要的甲烷温室气体排放源。而有机质参与下的硫循环过程是雨养型泥炭湿地重要的甲烷产生厌氧呼吸过程之一，持续性有机质—硫循环过程影响着泥炭湿地甲烷排放。本项目按照任务书的要求及年度计划，已基本完成既定研究任务。通过野外调查和室内培养实验，明确了淹水环境下天然有机质和硫素循环交互过程，定量了天然有机质和硫素循环交互过程对厌氧呼吸过程的影响，揭示了湿地生态系统温室气体排放规律及其重要影响因素。总之，研究发现有机质作为有机电子受体参与泥炭湿地厌氧呼吸过程并影响CO2和CH4排放，同时持续影响硫素氧化还原循环并进一步影响温室气体排放。截止到2019年底，已发表学术论文6篇，其中SCI论文5篇，中文核心期刊论文1篇；专著1部；已获得授权专利2项。在本项目支撑下，培养硕士研究生3名；项目执行期间项目组成员参加国内外学术会议交流多次；部分依托本项目发表的论文和申请授权的专著、专利，超过了项目任务书的既定目标。本项目研究结论对于深入认识气候变暖和外源硫输入影响下的北方泥炭湿地有机质—硫循环交互过程和预测未来气候变暖情境下泥炭地的温室气体排放具有重要意义。建议未来进一步改进研究方法，加强有机质—硫循环对泥炭地碳排放影响研究的同时还应深入研究该循环机制下的微生物参与过程。