湿地植物根系分泌物对根际氮转化菌群特征空间演化调控机制研究

Nitrogen cycling in wetlands has significantly effects on ecological structure, function and production of the systems. Nitrogen transformation in wetlands is mainly conducted by bioprocesses in rhizoshpere.Distribution of nitrogen transforming bacteria in rhizosphere is heterogeneous. Root exudate plays primary role in causing this feature as key transmitter for chemicals involved in rhizoshpere bioprocess. Elucidating the mechanisms of root exudates in shaping nitrogen transforming bacterial structures in rhizosphere will help to control rhizoshpere and give further insight into nitrogen cycling process in the underground environment. While the role and inside mechanisms of exudate in structuring nitrogen transfroming bacteria in rhizosphere remain unclear. Based on this situation, this project will choose typical wetland plant, Phragmites australis, as model to elucidate the mechanisms of its root exudate in shaping rhizobacterial structures through researches on 4 fundamental issues, i.e. micro-scale distribution of exudates in rhizosphere, effects of exudates on key abiotic eco-factors of micro-rhizosphere, chemotaxy of nitrogen transforming bacteria to exudates in micro-environments in rhizosphere, and metabolic profiles of nitrogen transforming bacteria on exudates. This project is to make people get better understand of plant-bacterial interactions in wetlands, spatial development of nitrogen transforming bacteria and nitrogen transforming process in rhizosphere. Results of this project promise to have great academic value with providing theoretical support to optimize root design of constructed wetland for wastewater treatment, regulate nitrogen transforming bacteria in rhizosphere and improve nitrogen-contaminants removal efficiency by related ecological wastewater treatment system.

湿地系统中氮的循环过程显著影响自身生态结构、功能和生产力，其氮的转化主要由根际生物过程完成。氮转化菌在根区呈不均匀分布状态，根系分泌物作为根际各化学物质参与生化反应的关键介质，对这一现象有重要影响。明确根系分泌物对根际氮转化菌的空间演化调控机制可促进掌控根区、理解根际氮循环过程，但关于其作用规律和内在机理尚未明确。针对此问题，本课题拟选取典型湿地植物芦苇，通过研究其根系分泌物在根际的微域分布特点、根系分泌物对根际关键非生物生态因子影响规律、根际微环境中氮转化菌对根系分泌物的趋化性、氮转化菌对根系分泌物的代谢功能等4个基本问题，揭示根系分泌物对根际氮转化菌作用机制，可促进人们对湿地植物-微生物互作机制、根际氮转化菌空间演化规律和根际氮转化过程的理解，研究成果预期可为优化人工湿地污水处理系统根区设计、合理调控氮转化菌群、提高相关生态水处理技术除氮效能提供科学依据，具有积极学术价值。

氮素作为主要营养元素之一，研究氮素在湿地系统中的循环过程有着很毋庸置疑的作用。湿地系统中氮的循环过程显著影响自身生态结构、功能和生产力，其氮的转化主要由根际生物过程完成。氮转化菌在根区呈不均匀分布状态，根系分泌物作为根际各化学物质参与生化反应的关键介质。通过本项目的资助，我们可以明确根系分泌物对根际氮转化菌的空间演化调控机制，充分掌控根区、理解根际氮循环过程。本课题选取典型挺水湿地植物芦苇作为研究对象。构建了根箱微域取样方法和琼脂培养基微域取样法，构建了根际复杂条件下根系分泌物取样方法，利用GC-MS分析了根系分泌物组成与分布特征，共检测出了99种化合物，包括34种烷烃、10 种烯烃、16种芳香烃、3种醇、2种酚、2种醚、2种酮、2种醛、1种酸、23种酯、1种噻唑以及3种其他含硫代、卤代化合物。研究了近根区远根区氮循环菌分布特征，结果表明芦苇根际硝化强度和反硝化强度大小的时间顺序一致：7月>9月>4月≈12月，而非根际基质硝化强度和反硝化强度随时间均无显著变化；根际基质硝化强度相对于非根际基质显著偏大，平均大约10倍以上；近根区的反硝化强度远远大于远根区(近根区>100倍远根区)；利用高通量分析方法，定量研究了氨氧化古菌（Ammonia-Oxidizing Archaea, AOA）和氨氧化细菌（Ammonia-Oxidizing Bacteria, AOB）两大类特种菌群在芦苇湿地近根区和远根区范围内对氨氧化作用的贡献，结果表明近根区和远根区均存在AOA和AOB，但AOA占明显的优势地位，古菌amoA基因丰度比细菌amoA基因丰度最高可高出4个数量级；AOB的amoA基因丰度和硝化速率均与深度呈现负相关，相关分析表明的硝化速率与AOB的amoA基因的丰度呈现显著的正相关关系，而与AOA的amoA基因则不存在相关关系。

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