Microbial Ecology Of Nitrite-dependent Anaerobic Ammonia Oxidation And Anaerobic Methane Oxidation In Wetlands

Nitrite-dependent anaerobic ammonium oxidation (ANAMMOX) and anaerobic methane oxidation (N-DAMO), which both use the nitrite as the electron acceptor, are two of the most recent discoveries in microbial nitrogen cycle and carbon cycle. The discoveries of these two microbial processes make great contributions to complete the global nitrogen cycle and carbon cycle.The previous research of the ANAMMOX process mainly focuses on its importance in artificial and marine environments. For the N-DAMO, the research of this process is just in its infancy, and only a limited number of recent studies have reported the N-DAMO process in natural ecosystems. Wetlands are one of the most important ecosystems on earth. The primary objectives of the current study are to investigate the distribution, diversity, abundance and activities of ANAMMOX bacteria and N-DAMO bacteria and their contributions to nitrogen cycle in different types of wetlands, including freshwater wetlands and coastal wetlands. Furthermore, the importance of these two processes in alleviating global warming and eutrophication was also investigated. The major results are as follows:1) The community structures of ANAMMOX bacteria and N-DAMO bacteria in wetland systems were investigated.①The community structures of ANAMMOX bacteria in wetland systems were investigated. Different genera of ANAMMOX bacteria and several novel ANAMMOX bacterial clusters were found together in the examined freshwater and coastal wetlands, suggesting a higher diversity of ANAMMOX bacteria. Candidatus Kuenenia and Candidatus Brocadia were the dominant ANAMMOX genera in the freshwater wetlands. In the coastal wetlands, Candidatus Kuenenia and Candidatus Brocadia were the dominant genera in the inner part of coastal wetlands with strong anthropogenic nitrogen pollution, while Candidatus Scalindua was the dominant genus in the outer part with less nitrogen pollution. It was found that the sediment/soil organic carbon content and inorganic nitrogen (ammonium and nitrate) content had the most important impact on the community structures of ANAMMOX bacteria in the freshwater wetlands. In the coastal wetlands, the nitrate concentration in porewater or overlying water had the most important impact on the community structures of ANAMMOX bacteria.②The community structures of N-DAMO bacteria in wetland systems were investigated. Different clusters of N-DAMO bacteria related to Candidatus Methylomirabilis oxyfera were simultaneously detected in the examined freshwater and coastal wetlands, suggesting a higher diversity of N-DAMO bacteria. The group A of N-DAMO bacteria (which were the dominant bacteria responsible for N-DAMO process) were mainly present at the deep layer of freshwater wetland soils, while the group B members were mainly present at the surface layer of freshwater wetland soils. In the coastal wetlands, the group A of N-DAMO bacteria were mainly detected in the inner part, while the group B members were mainly detected in the outer part. It was found that the sediment/soil organic carbon content and the methane concentration in soil gas had the most important impact on the community structures of N-DAMO bacteria in the freshwater wetlands. The sediment organic carbon content and nitrate concentration in porewater or overlying water had the most important impact on the community structures of N-DAMO bacteria in the coastal wetlands.2) The abundance of ANAMMOX bacteria and N-DAMO bacteria in wetland systems was investigated.①The abundance of ANAMMOX bacteria in wetland systems was investigated. Large numbers of ANAMMOX bacteria were detected in the examined freshwater and coastal wetlands, with105-107copies g-1soil. The abundance of ANAMMOX bacteria in the surface layer of freshwater wetland soils was obviously higher than that in the deep layer of soils. In the coastal wetlands, the abundance of ANAMMOX bacteria in the inner part was obviously higher than that in the outer part. It was found that the sediment/soil organic carbon content and inorganic nitrogen (ammonium and nitrate) content had the most important impact on the abundance of ANAMMOX bacteria in the freshwater wetlands. The nitrate concentration in porewater or overlying water had the most important impact on the abundance of ANAMMOX bacteria in the coastal wetlands.②The abundance of N-DAMO bacteria in wetland systems was investigated. Large numbers of N-DAMO bacteria were also detected in the examined freshwater and coastal wetlands, with105-107copies g-1soil. The abundance of N-DAMO bacteria in the deep layer of freshwater wetland soils was obviously higher than that in the surface layer of soils. In the coastal wetlands, the abundance of N-DAMO bacteria in the inner part was obviously higher than that in the outer part. It was found that the sediment/soil organic carbon content and the methane concentration in soil gas had the most important impact on the abundance of N-DAMO bacteria in the freshwater wetlands. The nitrate concentration in porewater or overlying water had the most important impact on the abundance of N-DAMO bacteria in the coastal wetlands.3) The activities and relative significance of ANAMMOX bacteria and N-DAMO bacteria in wetland systems were investigated.①The activity and relative significance of ANAMMOX bacteria in wetland systems were investigated. Extensive ANAMMOX activities were observed in the examined freshwater and coastal wetlands, with the potential rates ranging from2.8to89.7nmol N2g-1soil d-1. The contribution of ANAMMOX to dinitrogen gas production the examined wetlands was1.3%-46.7%. The potential ANAMMOX rates in the surface layer of freshwater wetland soils were obviously higher than those in the deep layer of soils. In the coastal wetlands, the potential ANAMMOX rates in the inner part were obviously higher than those in the outer part. It was found that the soil inorganic nitrogen (ammonium) content had the most important impact on the activity of ANAMMOX bacteria in the freshwater wetlands. The nitrate concentration in porewater or overlying water had the most important impact on the activity of ANAMMOX bacteria in the coastal wetlands.②The activity and relative significance of N-DAMO bacteria in wetland systems were investigated. Extensive N-DAMO activities were observed in the examined freshwater and coastal wetlands as well, with the potential rates ranging from0.1to14.5nmol CO2g-1soil d-1. The contribution of N-DAMO to total methane oxidation in the examined wetlands was1.0%-9.5%. The potential N-DAMO rates in the deep layer of freshwater wetland soils were obviously higher than those in the surface soils. In the coastal wetlands, the potential N-DAMO rates in the inner part were obviously higher than those in the outer part. It was found that the methane concentration in soil gas had the most important impact on the activity of N-DAMO bacteria in the freshwater wetlands. The nitrate concentration in porewater or overlying water had the most important impact on the activity of N-DAMO bacteria in the coastal wetlands.4) The ecological effects of the ANAMMOX process and N-DAMO process in wetland systems were assessed.①The ecological effects of the ANAMMOX process in wetland systems were assessed. It is estimated that the nitrogen flux via the ANAMMOX process in the examined freshwater and coastal wetlands is24.8-116.1g Nm-2year-1, suggesting that the ANAMMOX process is an important part of the wetland nitrogen cycle and plays an important role in balancing the wetland nitrogen budget. Furthermore, the ANAMMOX process could remove10.3%-48.1%of nitrogen loading in wetland systems. This indicates that the ANAMMOX process is an important nitrogen sink in wetlands, which can alleviate eutrophication of rivers, lakes and coastal water to a large extent.②The ecological effects of the N-DAMO process in wetland systems were assessed. It is estimated that the nitrogen flux via the N-DAMO process in the examined freshwater and coastal wetlands is1.0-5.4g Nm-2year-1, suggesting that the N-DAMO could also play a role in balancing the wetland nitrogen budget. Furthermore, the N-DAMO process could remove0.4%-2.2%of nitrogen loading in wetland systems. This indicates that the N-DAMO process can be served as a nitrogen sink as well, and plays a role in alleviating water eutrophication. In addition, a total of 0.5-2.0g CH4m-2year-1could be oxidised via the N-DAMO process in the examined wetlands. Base on this N-DAMO rate, it is estimated that totally4.0-20.0Tg CH4year-1could be oxidised via the N-DAMO process in wetland systems at the global level, which accounts for2.0%-20.0%total methane flux (100.0-200.0Tg CH4year-1) from the wetlands. This demonstrates that the N-DAMO process is a previously overlooked methane sink in wetland systems.