ABSTRACT: Benthic microbial communities contribute to nitrogen (N) cycling in coastal ecosystems through taxon-specific processes such as anammox, nitrification and N-fixation and community attributed pathways such as denitrification. By measuring the total (DNA-based) and active (RNA-based) surface sediment microbial community composition and the abundance and activity profiles of key N-cycling genes in a semi-enclosed embayment—Port Phillip Bay (PPB), Australia—we show that although the total relative abundance of N-cycling taxa is comparatively lower close to estuary inputs (Hobsons Bay [HB]), the capacity for this community to perform diverse Ncycling processes is comparatively higher than in sediments isolated from inputs (Central PPB [CPPB]). In HB, seasonal structuring of the sediment microbial community occurred between spring and summer, co-occurring with decreases in the activity profiles of anammox bacteria and organic carbon content. No changes were detected in the activity profiles of nitrifiers or the community-based pathway denitrification. Although no seasonal structuring of the sediment microbial community occurred in CPPB, the activity profiles of key N-cycling genes displayed comparatively higher within-site variability. These results show that despite N-cycling taxa representing a smaller fraction of the total community composition in estuary impacted sediments (HB) these microbial communities consistently engage in N-cycling processes and that seasonal instability in the composition of this community is not reflective of changes in its capacity to cycle N through coupled nitrification-denitrification but potentially via changes within the anammox community.

中文翻译：

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底栖生物通量季节变化的沿海沉积物微生物群落中的氮循环

摘要：底栖微生物群落通过特定的分类单元过程（例如厌氧氨氧化，硝化和固氮）和群落归因途径（例如反硝化），促进了沿海生态系统中的氮（N）循环。通过测量半封闭通道（澳大利亚菲利普港湾（PPB））中全部（基于DNA）和活性（基于RNA）的表面沉积物微生物群落组成以及关键N循环基因的丰度和活性谱，我们研究表明，尽管N循环类群的总相对丰度相对较低，接近河口投入物（Hobsons Bay [HB]），但该群落进行各种Ncycling过程的能力却比从投入物中分离出来的沉积物要高（中央PPB [ CPPB]）。在HB，春季和夏季之间发生了沉积物微生物群落的季节性结构，会同时导致厌氧菌和有机碳含量降低。在硝化器的活性谱或基于社区的途径反硝化过程中未检测到任何变化。尽管CPPB中没有沉积物微生物群落的季节性结构，但关键的N循环基因的活性谱显示相对较高的位点内部变异性。这些结果表明，尽管N循环类群在河口沉积物（HB）中只占总群落组成的较小部分，但这些微生物群落始终参与N循环过程，并且该群落组成的季节性不稳定性不能反映变化通过耦合硝化-反硝化作用（但可能通过厌氧氨氧化菌群落内部的变化）使N循环的能力。