Microbial Ecology Of Ammonia-oxidizing Archaea (AOA) And Ammonia-oxidizing Bacteria(AOB) In Typical Ecosystems

The ammonia oxidation was thought to be performed by ammonia-oxidizing bacteria in the last 100 years. The discovery of ammonia-oxidizing archaea (AOA) chanllenged our tradtional idea of ammonia oxidation and is of great importance to global nitrogen cycle. It also forced us to revaluate the ammonia oxidation process even the nitrogen cycle flux in nature. Nowdays, it is unknown whether the two ammonia-oxidizing microbes with the same ecological function display functional redundancy or niche differentiation due to complete competition. Also the relationship between environmental factors and the relative contributions of AOA and AOB to ammonia oxidation in different ecosystems is unclear. Figure out the relationship between environmental factors and the relative contributions of AOA and AOB to ammonia oxidation is of great importance to revaluate the ammonia oxidation process even the nitrogen cycle flux in nature. Based on the concentration of oxygen, natural ecosystems are divided into aerobic, hypoxic and aerobic/hypoxic alternant ecosystems. The primary objectives of the current study are to investigate the main factors influencing the abundance, diversity, community strctures and relative contributions of AOA and AOB in the three types of ecosystems. Also, simulated soil columns were used to study the effect of oxygen on the abundance, diversity, community strctures and relative contributions of AOA and AOB. The major results are as follows:1) The main environmental factors influencing the abundance, diversities and community strctures of AOA and AOB were investigated in aerobic ecosystem (Chinese agricultural soils).The abundance of AOA was 1-2 orders of magnitude more than that of AOB in Chinese agricultural soils, indicating AOA may be the main driver of ammonia oxidation in these soils. The soil pH was the key factor influencing the abundance of AOA. The diversity of AOA was higher than AOB in Chinese agricultural soils, with AOA contained 666 OTUs and AOB contained 454 OTUs. The soil pH was the most important factors influencing the ratios of AOA/AOB OTU numbers in these soils.The community strctures of AOA and AOB in Chinese agricultural soils were investigated. In most of the soils, AOA belonging to Nitrososphaera/Nitrososphaera sister cluster was the dominant AOA. While, in the soils with pH below 6.0, AOA belonging to Nitrosotalea cluster became dominant AOA. Nireosospira was the dominant AOB in all soil samples. It was found that soil pH had the most important impact on the community strctures of AOA and AOB in Chinese agricultural soils.2) The main environmental factors influencing the abundance, diversities and community strctures of AOA and AOB were investigated in hypoxic ecosystem (Qiantang River sediments).The abundance of AOA was lorder of magnitude more than that of AOB in Qiantang River sediments. The abundance of AOA and the ratios of AOA/AOB abundance showed obvious spatial variation characteristics. From upstream to downstream, the abundance of AOA and ratios of AOA/AOB abundance decreased gradually. The sediment pH, ammonium content and total inorganic nitrogen content were the key factors influencing the abundance of AOA in the sediment. The diversity of AOA and AOB also displayed spatial variation characteristics. From upstream to downstream, the diversity of AOA decreased and the diversity of AOB increased. The sediment pH, ammonium content, total inorganic nitrogen content and organic carbon were the most important factors influencing the diversities of AOA and AOB in Qiantang River sediments. AOA belonging to Nitrososphaera/Nitrososphaera sister cluster was the dominant AOA and Nireosospira was the dominant AOB in the Qiantang River.3) The main environmental factors influencing the abundance, diversities and community strctures of AOA and AOB were investigated in freshwater-type aerobic/hypoxic alternant ecosystem (water-level-fluctuating zones in Three Gorges Reservoir).The abundance of AOA and AOB in water-level-fluctuating zones in Three Gorges Reservoir were quantified. The abundance of AOA and AOB were always lower in the periodical-flooded soils compared with the corresponding non-flooded soils. The ratios of AOA/AOB abundance were always higher in the periodical-flooded soils, indicating that AOA might be more adaptable in the hypoxic environments compared to AOB. The soil ORP (Oxidation-Reduction Potential) was the key factor influencing the abundance of AOA and AOB. The diversity of AOA (90 OTUs) was higher than AOB (71 OTUs) in water-level-fluctuating zones in Three Gorges Reservoir. The diversity of AOA was higher in the periodical-flooded soils compared with the corresponding non-flooded soils, while the diversity of AOB showed the opposite pattern. The soil pH and ORP were the most important factors influencing the diversities of AOA and AOB in water-level-fluctuating zones in Three Gorges Reservoir. AOA belonging to Nitrososphaera/Nitrososphaera sister cluster was the dominant AOA and Nireosospira was the dominant AOB in all of the soils. It was found that soil ORP had the most important impact on the community strctures of AOA in water-level-fluctuating zones in Three Gorges Reservoir.4) The main environmental factors influencing the abundance, diversities, community strctures and activities of AOA and AOB were investigated in marine-type aerobic/hypoxic alternant ecosystem (intertidal zones in Zhoushan Island).The abundance of AOA and AOB in intertidal zones in Zhoushan Island were quantified. The abundance of AOA, AOB and the ratios of AOA/AOB abundance showed obvious temporal and spatial variation characteristics. The abundance of AOA in summer was higher than the other three seasons. From intertidal zones to subtidal zones, the abundance of AOA and the ratios of AOA/AOB increased, the abundance of AOB decreased. The sediment temperature, moisture content and total nitrogen content were the key factors influencing the abundance of AOA and AOB in intertidal zones in Zhoushan Island. The diversity of AOA was always higher than that of AOB in the sediments. From intertidal zones to subtidal zones, the diversity of AOA and AOB were both decreased. The sediment temperature was the most important factor influencing the diversity of AOB. AOA belonging to Nitrosopumilus cluster was the dominant AOA and Nireosospira was the dominant AOB in the sediments. It was found that sediment ORP had the most important impact on the community strctures of AOA in intertidal zones in Zhoushan Island. The ammonia oxidation rates of AOA and AOB displayed obvious temporal and spatial variation characteristics. In winter the total ammonia oxidation rates, the ammonia oxidation rates of AOB and the relative contribution of AOB were lower than the other three seasons. From intertidal zones to subtidal zones, the ammonia oxidation rates and relative contribution of AOA increased, while AOB showed the opposite pattern. In intertidal zones where the oxygen concentrations were higher, ammonia oxidation in the sediments was dominanted by AOB. While in subtidal zones where oxygen concentrations were lower, ammonia oxidation in the sediments was dominanted by AOA.5) The effect of oxygen concentration on the abundance, diversity, community strctures and relative contributions of AOA and AOB was investigated using simulated soil columns.Oxygen concentration determined the ratios of AOA/AOB abundance. In the flooded and periodic-flooded soil columns where the oxygen concentrations were relative lower, the ratios of AOA/AOB abundance became higher with the increase of incubation time. While in the dry soil column where the oxygen concentrations were relative higher, the ratios of AOA/AOB abundance became lower with the increase of incubation time.Oxygen concentration determined the ratios of AOA/AOB OTU numbers. In the flooded and periodic-flooded soil columns where the oxygen concentrations were relative lower, the ratios of AOA/AOB AOA/AOB OTU numbers became higher with the increase of incubation time. While in the dry soil column where the oxygen concentrations were relative higher, the ratios of AOA/AOB OTU numbers became lower with the increase of incubation time.Oxygen concentration determined the relative contributions of AOA and AOB in ammonia oxidation. In the flooded and periodic-flooded soil columns where the oxygen concentrations were relative lower, the relative contribution of AOA increased gradually and the relative contribution of AOB decreased gradually; in the dry soil column where the oxygen concentrations were relative higher, the changing pattern of the relative contribution of AOA and AOB was opposite compared with the flooded and periodic-flooded soil columns.