| Aerobic ammonia oxidation is carried out by ammonia-oxidizing bacteria(AOB)and archaea ammonia-oxidizing bacteria(AOA).In recent years,more and more attention has been paid to the ecological functions of these ammonia-oxidizing microorganisms.The community structure and ecological function of ammonia-oxidizing microorganisms in soil,especially in wetland soil,have become the focus of recent researches.Ammonia oxidation is one of the most important speed-limiting steps in the earth's nitrogen cycle and the first step for ammonia to re-enter the atmospheric nitrogen pool.Therefore,the relationship between ammonia oxidation microorganisms and the environment and their role in the ecosystem have attracted wide attention.Five representative swamp wetlands with intact primitive ecological environment were selected in the northern alpine region represented by Heilongjiang Province.The 16 S r RNA gene of prokaryotes and amo A gene of ammonia-oxidizing bacteria were sequenced by the second generation sequencing technology.Based on the analysis of the biodiversity of the two molecular biomarker genes,the spatio-temporal variations of the community of AOA and AOB in cold swamp wetlands and the relationship between the community composition and carbon and nitrogen content in soil were studied.The correlation between the relative abundance of AOA,AOB,nitrite oxidizing bacteria(NOB),methane oxidizing bacteria(MOB)and methanogens was also investigated.The Nitrososphaera subcluster 1 is the most abundant AOA lineage in cold marsh soil.The Nitrosotalea cluster,an acidophilic AOA lineage,showed higher relative abundance in the soils of Honghe wetland,Sanjiang wetland and Mohe wetland,which had low soil p H.However,Nitrosotalea cluster required higher in-situ oxygen content than Nitrososphaera subcluster 1 did.In the surface soils which were immersed in water,its relative abundance is very low,even though it is acidic soil.This phenomenon was due to the extreme hypoxia.The Nitrosopumilus cluster is mostly found in neutral and water-immersed soils,mainly in Qixing River wetland,which is often accompanied by interference of exogenous nutrients.AOB in cold wetland soils belongs mostly to Nitrosomonadaceae.In horizontal dimension,AOA community showed a highly similarity in the same wetland soil,although there were slight differences between AOA communities under different vegetation conditions in the same wetland,the difference was not as remarkable as that between wetlands.In vertical dimension,the diversity of AOA decreased gradually from surface layer to deep layer in the soil without or with shallow water covered.but in wetland soil with deep water coverage,AOA diversity was most abundant in middle layer which was affected by plant rhizosphere.AOA accounted for 0.004%-0.29% of the prokaryotic community and AOB accounted for 1.4%-6.5% of the bacterial community.From the beginning of freeze-thaw period to the end of freeze-thaw period,the relative abundance of AOB decreased,while the relative abundance of AOB changed little from summer to autumn.The relative abundance of AOA is the lowest in winter,and increases in freeze-thaw period,usually at the end of freeze-thaw period and in summer growing season,and decreases in autumn.Among the microorganisms related to AOA and AOB in metabolism,methanogens are mostly Methanomicrobia,which is the main component of Euryarchaeota.The NOB community is mainly composed of Nitrospirae and Nitrotoga.The community diversity of methane oxidizing bacteria(MOB)is higher,but the relative abundance is only 0.01%-0.59%.Among these microorganisms,the relative abundance of AOA was weakly negatively correlated with that of AOB,but the relative abundance of AOA was negatively correlated with that of MOB and methanogens(P < 0.01).In the extreme anoxic and even anaerobic environment of wetland soil,the competition of AOA,AOB and MOB for oxygen is the main cause of their negative correlation. |
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