长江中游芦苇滩地CH4通量组分区分及环境调控机制

Not dividing the components of CH4 flux caused the CH4 fluxes dynamics unaccountable and their environmental controls unclear.The well-developed aerenchyma of Phragmites Australis not only can promote CH4 escaping from soil but also can help O2 delivering to the soil. Thus, theoretically, a Phragmites Australis ecosystem has large potential of CH4 sequestration. Our prelimiary results showed that the CH4 absorption by Phragmites Australis ecosystem on the floodplain in the middle reaches of Yangtze River was more than twice as large as the maximum of a forest ecosystem, which implied that the Phragmites Australis ecosystem in this region may have different characteristics on CH4 flux as well as regulatory mechanism. This research is going to conduct a continuously 3 yr. observation on CH4 flux of Phragmites Australis ecosystem on the floodplain in the middle reaches of Yangtze River with eddy covariance method, in order to reveal the ecosystem CH4 variation at different time scales and its budget on atmospheric CH4. Meanwhile, the two main components of CH4 flux, i.e., net production and net oxidation, will be quantitatively partitioned with 13C stable isotope technique, and static chamber method will be used to observe CH4 flux from the soil and from the soil-plant system. All the environmental factors, including vegetation, micrometeorology and soil, will be observed synchronously. By doing these, the CH4 flux and its control factors will be discussed at macroscopic, medium and microcosmic level separately, and then the mechanism of environmental regulation on CH4 flux of the Phragmites Australis ecosystem in this region will be discovered by coupling analysis of the results of the three levels with SEM model.

CH4通量组分未被区分导致通量变化规律和环境调控因子不明确。芦苇发达的通气组织能同时为土壤CH4输出和O2输入提供通道，因此，理论上芦苇生态系统具备较强的CH4吸收潜力。预研究发现，长江芦苇滩地在未淹水夏季CH4吸收强度大于森林生态系统最大值2倍，暗示该区域芦苇滩地可能具有较其它芦苇湿地不同的CH4源汇功能和环境调控机制。本项目将基于涡度相关法对该区域芦苇滩地CH4通量进行为期3年连续观测，揭示研究区CH4通量变化特征和源汇功能；同时，以静态箱法对比观测土壤-大气、土壤-植被-大气界面CH4通量以厘清植被在地表CH4通量中的贡献，以13C稳定同位素技术定量区分土壤CH4通量的净产生和净氧化分量，结合不同尺度同步观测的环境因子，在宏观、中观和微观三个层次探讨CH4通量过程及环境调控作用，并基于SEM模型对三个层次通量过程及环境调控机制进行耦合分析，揭示芦苇滩地CH4通量主控因子及其调控机制。

甲烷(CH4)是仅次于二氧化碳（CO2）的重要温室气体。由于CH4通量过程复杂，且缺乏高时空分辨率的观测，目前仍难以准确模拟和估算自然生态系统中CH4排放量。湿地是陆地生态系统重要碳库，同时也是最主要的CH4的源。芦苇发达的通气组织能同时为土壤CH4输出和O2输入提供通道，因此，理论上芦苇滩地在非淹水状态下具备较强的CH4吸收潜力。预研究发现，长江芦苇滩地在未淹水夏季CH4吸收强度大于森林生态系统最大值2倍，暗示该区域芦苇滩地可能具有较其它芦苇湿地不同的CH4源汇功能和环境调控机制。本项目基于涡度相关闭路系统对该区域芦苇滩地CH4通量进行了为期1年多连续观测，初步揭示研究区CH4通量变化特征及驱动因子，结果显示：（1）CH4通量具有明显的季节变化，表现为淹水季显著高于非淹水季。（2）淹水季CH4通量表现出显著的日变化特征，呈现白天高而晚上低的特点，其变化幅度为30~320nmol•m-2•S-1。（3）淹水季CH4通量日变化规律不明显，同时呈现出了CH4的吸收和排放，其变化幅度大约在-10～10nmol•m-2•S-1之间，整体表现为CH4中性或微弱的CH4排放。（4）水位是调节CH4通量的关键因子。当水位上升至-1.6m时，CH4通量开始增大；在水位达到-0.8～-0.6m时，CH4通量排放最大（平均值达到320nmol•m-2•S-1）；当水位在-0.4～0.4m时，CH4通量保持在较高水平（～200nmol•m-2•S-1）；之后，随着水位的上升，CH4排放量有所降低。此外，依托本项目，研制了一款土壤-大气界面其通量观测箱，提高了野外采集气样的便捷性；同时研发了“一种两级多通道大气采集管路过滤系统”，将基于DLT100 快速CH4分析仪的CH4通量闭路系统的连续免维护运行时间从7天延长至60余天，极大提升了CH4通量闭路系统的运行效率。