The South China Sea (SCS), the largest marginal sea in the Western Pacific Ocean, is a huge oligotrophic water body with very limited influx of nitrogenous nutrients. This suggests that sediment microbial N(2) fixation plays an important role in the production of bioavailable nitrogen. To test the molecular underpinning of this hypothesis, the diversity, abundance, biogeographical distribution, and community structure of the sediment diazotrophic microbiota were investigated at 12 sampling sites, including estuarine, coastal, offshore, deep-sea, and methane hydrate reservoirs or their prospective areas by targeting nifH and some other functional biomarker genes. Diverse and novel nifH sequences were obtained, significantly extending the evolutionary complexity of extant nifH genes. Statistical analyses indicate that sediment in situ temperature is the most significant environmental factor influencing the abundance, community structure, and spatial distribution of the sediment nifH-harboring microbial assemblages in the northern SCS (nSCS). The significantly positive correlation of the sediment pore water NH(4)(+) concentration with the nifH gene abundance suggests that the nSCS sediment nifH-harboring microbiota is active in N(2) fixation and NH(4)(+) production. Several other environmental factors, including sediment pore water PO(4)(3-) concentration, sediment organic carbon, nitrogen and phosphorus levels, etc., are also important in influencing the community structure, spatial distribution, or abundance of the nifH-harboring microbial assemblages. We also confirmed that the nifH genes encoded by archaeal diazotrophs in the ANME-2c subgroup occur exclusively in the deep-sea methane seep areas, providing for the possibility to develop ANME-2c nifH genes as a diagnostic tool for deep-sea methane hydrate reservoir discovery.

中文翻译：

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南海北部沉积物 nifH 栖息微生物群的环境依赖性分布。

南海（SCS）是西太平洋最大的边缘海，是一个巨大的贫营养水体，含氮养分的流入非常有限。这表明沉积物微生物 N(2) 固定在生物可利用氮的生产中起着重要作用。为了检验这一假设的分子基础，在河口、沿海、近海、深海和甲烷水合物储层或其预期的 12 个采样点调查了沉积物固氮微生物群的多样性、丰度、生物地理分布和群落结构。通过靶向 nifH 和其他一些功能性生物标志物基因。获得了多样化和新颖的 nifH 序列，显着扩展了现存 nifH 基因的进化复杂性。统计分析表明，沉积物原位温度是影响南海北部 (nSCS) 沉积物 nifH 微生物组合的丰度、群落结构和空间分布的最重要环境​​因素。沉积物孔隙水 NH(4)(+) 浓度与 nifH 基因丰度的显着正相关表明 nSCS 沉积物 nifH 栖息微生物群在 N(2) 固定和 NH(4)(+) 生产中是活跃的。其他几个环境因素，包括沉积物孔隙水 PO(4)(3-) 浓度、沉积物有机碳、氮和磷水平等，对于影响 nifH 栖息地的群落结构、空间分布或丰度也很重要。微生物组合。