湿地岸边带新型微生物氮循环过程的发生机制、热区分布及氧化亚氮减排的环境效应

Wetland riparian zones, the transitional areas between water bodies and upland terrestrial communities, have been globally shown to efficiently intercept runoff and pollutants from upland areas into streams, and play an important role especially in the removal of N pollutants via microbial N-cycle pathways. Due to active N reactions, riparian zones are regarded as hotspots for nitrous oxide (N2O) production in natural environment. The N-cycle is mainly driven by microorganisms, which transform different N compounds through a series of redox reactions. N-cycle studies have been conducted for the last hundred years. However, there is limited knowledge about the complexity of the process involved. This is particularly true for riparian zones due to their high heterogeneity. Novel microbial N cycle processes, such as anaerobic ammonium oxidation (anammox), complete ammonia oxidizers (comammox), nosZ clade II-type denitrification and dissimilatory nitrate reduction to ammonium (DNRA), gave us a brand new knowledge of the mechanisms of N cycle and N2O emission. .Financially supported by a series of NSFC funding, our previous investigation found the occurrence of anammox hotspots at land–freshwater interfaces of lake riparian zones in North China, as evidenced by molecular and isotopic tracing technologies. Moreover, with static chambers and control experiments, these anammox hotspot zones showed less N2O emissions flux compared with the tests without anammox biomass during a 12 month testing period. In stark contrast, both polymerase chain reaction (PCR) and 15N tracing screening showed negative results from landward soils, which was only 5 m away from interface hotspots in the riparian zone (reported by Nature Geoscience). Based on our and others’ previous studies on microbial N-cycles in wetland riparian zones, we propose the hypothesis that different N-cycle processes may have distinct spatial-temporal hotspots in riparian zones. .This project aims to explore the mechanisms, hotspots and contribution of the above novel microbial N-cycle processes in riparian zones with special on N2O mitigating, using advanced 15N-18O isotopic tracing, traditional 15N isotopic tracing, high-throughput sequencing and metagenomic technique targeted key functional genes. The results of this project are expected to supplement and revise the theory system of N-cycle in aquatic and wetland ecosystems, therefore has significant influence on global N-cycle balance and N2O flux.

湿地岸边带是陆地与水体之间的过渡区，具有很强的氧化还原梯度，是温室气体N2O释放热区。新型氮循环反应和功能微生物的发现，如厌氧氨氧化、完全硝化、nosZ cladeII型反硝化和硝酸盐异化还原成氨，让我们重新认识氮循环机理，特别是N2O释放机制与环境效应。在自然基金连续资助下，本团队前期发现湖泊岸边带发生显著的厌氧氨氧化反应热区并减排N2O，但仅5米之隔的陆向土壤则不发生反应（成果刊于Nature Geoscience）。由此推测，氮循环过程在岸边带的发生具有明显更迭性和热区异质性，其微生物驱动机制和N2O释放效应值得深入研究。本项目拟采用先进的15N-18O稳定同位素双标记示踪、传统15N单标记示踪和针对关键功能基因的高通量和宏基因等多组学技术，深入研究湿地岸边带新型氮循环过程的发生机制与热区分布，探索N2O减排的环境效应。研究结果将对水生态系统氮循环模式和N2O通量模型计算有重要意义。

湿地岸边带是陆地和淡水生态系统的过渡区，频繁干湿交替使水/土、水/沉积物界面形成了广泛的且周期性更迭的缺氧-好氧界面，具有丰富的氧化还原电位梯度，通常被认为是氮循环转化的活跃区和温室气体N2O的高释放区。随着氮循环微生物中新物种、新过程和新功能的不断发现，对于湿地岸边带系统中氮循环微生物，尤其是新型物种、过程或功能及其区域环境效应的认识，更是尚不清晰。依托本项目支持，团队应用（q）PCR、15N同位素示踪和宏基因/转录组学等技术，研究湿地岸边带系统新型氮循环微生物过程及新型功能基因的发生机制，重点关注厌氧氨氧化（anammox）、完全氨氧化（comammox）和硝酸盐异化还原为铵（DNRA）等过程的活性区域、发生机制、过程效应及其对N2O减排的区域环境效应。

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