Nitrous oxide (N2O) is a potent greenhouse gas of primarily microbial origin. Oxic and anoxic emissions are commonly ascribed to autotrophic nitrification and heterotrophic denitrification, respectively. Beyond this established dichotomy, we quantitatively show that heterotrophic denitrification can significantly contribute to aerobic nitrogen turnover and N2O emissions in complex microbiomes exposed to frequent oxic/anoxic transitions. Two planktonic, nitrification-inhibited enrichment cultures were established under continuous organic carbon and nitrate feeding, and cyclic oxygen availability. Over a third of the influent organic substrate was respired with nitrate as electron acceptor at high oxygen concentrations (> 6.5 mg/L). N2O accounted for up to one quarter of the nitrate reduced under oxic conditions. The enriched microorganisms maintained a constitutive abundance of denitrifying enzymes due to the oxic/anoxic frequencies exceeding their protein turnover - a common scenario in natural and engineered ecosystems. The aerobic denitrification rates are ascribed primarily to the residual activity of anaerobically synthesized enzymes. From an ecological perspective, the selection of organisms capable of sustaining significant denitrifying activity during aeration shows their competitive advantage over other heterotrophs under varying oxygen availabilities. Ultimately, we propose that the contribution of heterotrophic denitrification to aerobic nitrogen turnover and N2O emissions is currently underestimated in dynamic environments.

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好氧反硝化作为微生物群落的 N2O 来源


一氧化二氮 (N2O) 是一种主要由微生物产生的强效温室气体。含氧和缺氧排放通常分别归因于自养硝化和异养反硝化。除了这种既定的二分法之外，我们定量地表明，异养反硝化可以显着促进暴露于频繁的有氧/缺氧转变的复杂微生物组中的需氧氮周转和 N2O 排放。在连续有机碳和硝酸盐供给以及循环氧可用性下建立了两种浮游、硝化抑制富集培养物。超过三分之一的流入有机底物在高氧浓度 (> 6.5 mg/L) 下以硝酸盐作为电子受体进行呼吸。 N2O 占有氧条件下还原的硝酸盐的四分之一。由于好氧/缺氧频率超过其蛋白质周转率（自然和工程生态系统中的常见情况），富集的微生物保持了反硝化酶的组成丰度。需氧反硝化率主要归因于厌氧合成酶的残余活性。从生态角度来看，选择能够在通气过程中维持显着反硝化活性的生物体，显示出它们在不同氧气利用率下相对于其他异养生物的竞争优势。最终，我们提出，在动态环境中，异养反硝化对好氧氮周转和 N2O 排放的贡献目前被低估。