南极苔原卤甲烷源汇过程及其调控机理研究

Methyl halides are the main materials for the destruction of the ozone layer, and they are also important greenhouse gases and trace organic pollutants. With the implementation of the Montreal Protocol and its amendments, the studies on the methyl halide emissions from the natural sources on the land have increasingly become the research hotspots for environmental sciences, but there is no report about the processes of the sources and sinks for atmospheric methyl halides from Antarctic tundra ecosystem. In this project, tundra ecosystem on the Fildes Peninsula of maritime Antarctica is selected to be as study area, and the patterns for the temporal and spatial variations of methyl halides and their affecting factors will be studied to find out the key factors affecting tundra methyl halide fluxes based upon field observation and the laboratory simulation experiments. In addition, we will use stable isotope tracer technique and soil incubation experiments to study the differences of gross production and gross consumption for methyl halides and their influencing factors in different types of tundra soils. The variation characteristics of the carbon stable isotopes will be made certain in methyl halides emitted from Antarctic tundra ecosystem, and the mechanisms of the production and consumption for tundra methyl halides will also be explored in this project. Finally, we will establish a model between net methyl halide fluxes and environmental factors, and will explore the effects of the changing function of sources and sinks for methyl halides in Antarctic tundra on the ozone hole recovery and atmospheric environment. The results of this project will reveal the processes of the biogeochemical cycles for methyl halides in Antarctic tundra ecosystem under extreme environment, and will further promote people to understand the processes of sources and sinks for methyl halides and their regulatory mechanisms in Antarctic tundra environment, and will provide the scientific basis to reasonably evaluate and predict the contribution of Antarctic tundra ecosystem to methyl halide emissions in the atmosphere.

卤甲烷是破坏臭氧层的主要物质，是重要的痕量温室气体和有机污染物。随着《蒙特利尔议定书》及其修正案的实施，对陆地自然源卤甲烷排放的研究日益成为环境科学的热点，但目前还未见有南极苔原卤甲烷源汇过程研究的报道。本项目以南极法尔兹半岛苔原作为研究区域，通过野外观测与室内模拟实验，研究苔原卤甲烷通量的时空变化规律及其影响因素，查明影响苔原卤甲烷通量变化的关键因子；通过稳定同位素示踪技术与土壤培养实验，研究苔原土壤卤甲烷总产生与总消耗通量的变化特征及其影响因素，明晰卤甲烷碳稳定同位素变化特征，探索苔原卤甲烷可能的产生与消耗的机制。建立卤甲烷通量与环境因子的模型，探讨南极苔原卤甲烷源汇功能变化对臭氧洞恢复与大气环境的影响。通过本课题的研究，将揭示南极极端环境下苔原卤甲烷的生物地球化学循环过程，推动人们对南极环境卤甲烷源汇过程及其调控机制的认识，为合理评估和预测南极苔原对大气卤甲烷的贡献量提供科学依据。

卤甲烷是破坏臭氧层的主要物质，也是重要的痕量温室气体和有机污染物。本项目以南极法尔兹半岛苔原作为研究区域，通过野外观测与室内模拟实验，研究了苔原卤甲烷、三氯甲烷和四氯化碳通量变化规律、源汇机制及其影响因素。发现南极苔原土壤总体上表现为CH3Cl和CH3Br的汇，且CH3Cl比CH3Br通量高一个数量级；普通苔原土壤对CH3Cl和CH3Br的消耗速率最大，企鹅粪和海豹粪的沉积同时促进了CH3Cl和CH3Br的产生而降低了汇强。热处理和有氧/厌氧培养实验表明：苔原土壤CH3Cl和CH3Br的消耗主要受微生物调控，而其产生是非生物过程，不受氧气含量制约。温度梯度培养实验揭示了温度增加促进了普通苔原土壤CH3Cl和CH3Br的消耗；冻融循环实验表明：南极苔原土壤在冻结期表现为CH3Cl排放源，且企鹅与海豹聚居区土壤排放通量显著高于普通苔原，而在融化期苔原土壤表现为CH3Cl吸收汇，且普通苔原CH3Cl吸收速率显著高于动物聚居区苔原，表明全球变暖将进一步增加苔原CH3Cl和CH3Br的汇强，取决于土壤湿度和非生物产生速率。查明南极苔原是重要的CHCl3排放源，每年向大气排放约100吨CHCl3；其产生偏好于透气性较高的土壤环境中微生物参与的酶促生物过程，且企鹅活动促进了CHCl3产生过程；苔原土壤在融化期CHCl3排放速率约是冻结期的3倍，且在夏季平均温度条件（约4℃）下苔原土壤呈现最大的CHCl3排放速率。发现苔原土壤是大气CCl4相对稳定的汇，每年吸收约2.4吨CCl4。证实了南极苔原对CCl4的降解是非生物地球化学反应为主导的过程，与O2含量有关，不受海洋动物活动和相关的有机质、卤素输入的影响；获得了CCl4相对于土壤汇的分生命周期为235-474年。此外，阐明了南极苔原土壤气态硒挥发特征以及硒生物地球化学过程，揭示了苔原土壤硝化和反硝化微生物活性、群落结构及其影响因素，解析了多环境因子对南极苔原温室气体通量的影响，以及苔原生态系统呼吸和光合期间CO2同位素组成及其与环境因子的关系等。.发表标有该项目资助号的论文总计17篇。通过该项目的研究，为我国在南极积累了大量的含卤的痕量气体浓度与通量等的资料，阐明了南极苔原卤素生物地球化学循环过程，推动了人们对南极环境含卤的痕量气体源汇过程及其调控机制的认识，为合理评估和预测南极苔原对大气卤甲烷的贡献量提供了科学依据。