Microorganisms in marine oxygen minimum zones (OMZs) drive globally impactful biogeochemical processes. One such process is multistep denitrification (NO 3 – →NO 2 – →NO→N 2 O→N 2 ), which dominates OMZ bioavailable nitrogen (N) loss and nitrous oxide (N 2 O) production. Denitrification-derived N loss is typically measured and modeled as a single step, but observations reveal that most denitrifiers in OMZs contain subsets (“modules”) of the complete pathway. Here, we identify the ecological mechanisms sustaining diverse denitrifiers, explain the prevalence of certain modules, and examine the implications for N loss. We describe microbial functional types carrying out diverse denitrification modules by their underlying redox chemistry, constraining their traits with thermodynamics and pathway length penalties, in an idealized OMZ ecosystem model. Biomass yields of single-step modules increase along the denitrification pathway when organic matter (OM) limits growth, which explains the viability of populations respiring NO 2 – and N 2 O in a NO 3 – -filled ocean. Results predict denitrifier community succession along environmental gradients: Pathway length increases as the limiting substrate shifts from OM to N, suggesting a niche for the short NO 3 – →NO 2 – module in free-living, OM-limited communities, and for the complete pathway in organic particle-associated communities, consistent with observations. The model captures and mechanistically explains the observed dominance and higher oxygen tolerance of the NO 3 – →NO 2 – module. Results also capture observations that NO 3 – is the dominant source of N 2 O. Our framework advances the mechanistic understanding of the relationship between microbial ecology and N loss in the ocean and can be extended to other processes and environments.

中文翻译：

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生态动力学解释了海洋中的模块化反硝化作用


海洋含氧最低区 （OMZ） 中的微生物推动了具有全球影响的生物地球化学过程。其中一种过程是多步反硝化 （NO 3– →NO 2– →NO→N 2 O→N 2 ），它主导着 OMZ 生物可利用氮 （N） 损失和一氧化二氮 （N 2 O） 的生产。反硝化衍生的 N 损失通常作为单个步骤进行测量和建模，但观察表明，OMZ 中的大多数反硝化剂都包含完整途径的子集（“模块”）。在这里，我们确定了维持不同反硝化剂的生态机制，解释了某些模块的普遍性，并研究了对氮损失的影响。我们在理想化的 OMZ 生态系统模型中描述了通过其潜在的氧化还原化学来执行各种反硝化模块的微生物功能类型，用热力学和途径长度惩罚来限制它们的特性。当有机物 （OM） 限制生长时，单步模块的生物量沿反硝化途径增加，这解释了在充满 NO 3- 的海洋中呼吸 NO 2– 和 N 2 O 的种群的生存能力。结果预测反硝化剂群落沿环境梯度的演替：随着限制底物从 OM 转移到 N，通路长度增加，表明在自由生活、OM 受限群落中短 NO 3– →NO 2– 模块和有机颗粒相关群落中的完整通路存在生态位，与观察结果一致。该模型捕获并机械地解释了观察到的 NO 3– →NO 2– 模块的优势和更高的氧耐受性。结果还捕捉到观察到 NO 3– 是 N 2 O 的主要来源。 我们的框架推进了对微生物生态学与海洋氮损失之间关系的机制理解，并且可以扩展到其他过程和环境。