水深梯度驱动下芦苇根孔微环境耦合反硝化的响应特征与机制

Nitrogen (N) is a key factor controlling water eutrophication, and denitification of wetlands plays an important role in N loading mitigation. In riparian wetlands, root channel system with various structures and large quantity is formed due to the complicated hydrological regime and combined biological activities. In the root channel system, the heterogeneity of Red-Ox condition is a significant factor driving the shifting of N storage and transformation. Nevertheless, few research has been carried out concerning at the environmental characteristics and coupled denitrification in “multi-media” root channel system, and less attention has been paid to the contribution of denitrification in root channel system. Chosen phragmites root channel in riparian wetland as the research target, the chemical composition and structure pattern of root channel “multi-media regime” will be obtained with three-dimensional CT scanning, three-dimensional Fluorescence Spectroscopy and microbial Metagenomic sequencing following the analysis of micro-interface environmental parameters. With the application of 15N isotope pairing and microelectrode technique, coupled denitrification dynamics and the contribution of nitrous oxide (N2O) and nitric oxide (NO) at the micro-environment of phragmites root channel driven by water depth gradient will be discussed. Based on the overall research, the micro-environmental effects, related coupled denitrification in different flooding conditions and the mechanisms will be revealed. It is expected that the study could help supplementing the N cycling theoretical system in the structure of “filter + biofilm” of root channel system, and could support the technical operation in N pollution mitigation and ecological restoration in eutrophied water columns.

氮是水体富营养化的关键限制因子，反硝化脱氮在湿地氮负荷削减中起着重要作用。湖滨带湿地的复杂的水文条件及多种生物作用构造了结构丰富、数量庞大的根孔系统，氧化还原异质性是根孔各结合态氮赋存及转化的重要驱动因子。然而，根孔“多介质体系”中的环境特征及耦合反硝化研究较为薄弱，在湿地内源氮循环中的作用未引起足够的重视。本研究以湖滨带湿地芦苇根孔为研究对象，在探明根孔微环境特征的基础上，结合三维CT扫描、三维荧光光谱分析及微生物宏基因组测序获取根孔“多介质体系”的物质组成与结构特征。借助15N同位素配对及微电极技术探索水深梯度驱动下芦苇根孔耦合反硝化的响应规律和N2O、NO的分布特征。基于以上研究，揭示不同淹水情形下根孔的微环境效应及耦合反硝化的受控机制，完善根孔系统“滤膜+微生物膜”结构的氮循环理论体系，为富营养化水体氮污染治理和生态修复提供技术支撑。

通过芦苇根孔反硝化脱氮过程研究，发现水深是限制芦苇根孔活性的主要限制性因子，其中溶解性有机碳是反硝化脱氮的主要限制因子之一。芦苇根孔存在氧化还原的异质性活性界面，是芦苇根孔反硝化主要热点。根孔微生物数据分析发现，根孔微生物nosZ基因种群是根孔微生物反硝化脱氮的主要优势物种，芦苇根系随水深变化明显，适度的水深条件是芦苇形态指标、生理指标及光合活性处于峰值，芦苇发挥反硝化脱氮效率高。芦苇根孔对湿地反硝化具有重要意义。