Abstract：
It is predicted that oxygen minimum zones (OMZs) in the ocean will expand as a consequence of global warming and environmental pollution. This will affect the overall microbial ecology and microbial nitrogen cycle. As one of the world\'s largest alluvial estuaries, the Yangtze Estuary has exhibited a seasonal OMZ since the 1980s. In this study, we have uncovered the microbial composition, the patterns of community assembly and the potential for microbial nitrogen cycling within the water column of the Yangtze Estuary, with a particular focus on OMZ. Based on the 16 S rRNA gene sequencing, a specific spatial variation in the composition of prokaryotic communities was observed for each water layer, with the Proteobacteria (46.1%), Bacteroidetes (20.3%), and Cyanobacteria (10.3%) dominant. Stochastic and deterministic processes together shaped the community assembly in the water column. Further, pH was the most important environmental factor influencing prokaryotic composition in the surface water, followed by silicate, PO43-, and distance offshore (p < 0.05). Water depth, NH4+, and PO43- were the main factors in the bottom water (p < 0.05). At last, species analysis and marker gene annotation revealed candidate nitrogen cycling performers, and a rich array of nitrogen cycling potential in the bottom water of the Yangtze Estuary. The determined physiochemical parameters and potential for nitrogen respiration suggested that organic nitrogen and NO3- (or NO2-) are the preferred nitrogen sources for microorganisms in the Yangtze Estuary OMZ. These findings are expected to advance research on the ecological responses of estuarine oxygen minimum zones (OMZs) to future global climate perturbations.
摘要：
据预测，由于全球变暖和环境污染，海洋中的最小氧气区（OMZ）将扩大。这将影响整个微生物生态和微生物氮循环。作为世界上最大的冲积河口之一,长江口自1980年代以来一直表现出季节性OMZ。在这项开创性的研究中，我们已经发现了微生物的组成，长江口水柱内的群落聚集模式和微生物氮循环潜力，特别关注OMZ。基于16SrRNA基因测序,每个水层都观察到原核生物群落组成的特定空间变化，与变形杆菌（46.1％），拟杆菌（20.3%），蓝藻(10.3%)占优势。随机和确定性过程共同形成了水柱中的社区集合。Further,pH是影响地表水中原核生物成分最重要的环境因子,其次是硅酸盐，PO43-,和离岸距离(p<0.05)。水深,NH4+,和PO43-是底水的主要因素（p<0.05）。最后,物种分析和标记基因注释揭示了候选氮循环表演者，长江口底水具有丰富的氮循环潜力。确定的理化参数和氮呼吸潜力表明，有机氮和NO3-（或NO2-）是长江口OMZ微生物的首选氮源。这些发现有望促进对河口最小氧气区（OMZ）对未来全球气候扰动的生态响应的研究。
