Mangrove forests are considered to be a highly productive ecosystem, but they are also generally nitrogen (N)-limited. Thus, soil N₂ fixation can be important for the stability of both mangrove ecosystem functions and upland N supply. This study evaluates the N₂ fixation activity and composition of relevant microorganisms in two coastal mangrove forests—the Guandu mangrove in an upstream estuary and the Bali mangrove in a downstream estuary—using the acetylene reduction method, real-time polymerase chain reaction, and next-generation sequencing. The results demonstrated that ambient nitrogenase activity was higher in downstream mangrove forests (13.2–15.6 nmol hr⁻¹ g⁻¹ soil) than in upstream mangrove forests (0.2–1.4 nmol hr⁻¹ g⁻¹ soil). However, both the maximum potential nitrogenase activity and nitrogenase gene (nifH gene) copy number were found to be higher in the upstream than in the downstream mangrove forests, implying that the nitrogenase activity and diazotrophic abundance may not necessarily be positively correlated. In addition, amended MoO₄ (which inhibits the activity of sulfate-reducing bacteria in N₂-fixation) yielded low nitrogenase activity, and sulfate-reducing bacteria made up 20–50% of the relative diazotrophic abundance in the mangrove forests, indicating that these bacteria might be the major active diazotrophs in this environment.

中文翻译：

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红树林土壤固氮微生物的组成及活性

红树林被认为是一个高产的生态系统，但它们通常也受氮 (N) 限制。因此，土壤 N ₂固定对于红树林生态系统功能和旱地 N 供应的稳定性非常重要。本研究利用乙炔还原法、实时聚合酶链反应等方法，对两片沿海红树林——上游河口的官渡红树林和下游河口的巴厘岛红树林——中的N ₂固定活性和相关微生物组成进行了评价。-代测序。结果表明，下游红树林（13.2-15.6 nmol hr ^-1 g ^-1土壤）的环境固氮酶活性高于上游红树林（0.2-1.4 nmol hr⁻¹ g ⁻¹土壤）。然而，发现上游的最大潜在固氮酶活性和固氮酶基因（nifH基因）拷贝数均高于下游红树林，这意味着固氮酶活性和固氮丰度可能不一定呈正相关。另外，修正的MoO ₄（其抑制在N-硫酸盐还原细菌的活性₂ -fixation）得到低固氮酶活性，和硫酸盐还原菌由20-50％的相对丰度固氮在红树林的，这表明这些细菌可能是这种环境中主要的活性固氮菌。