Agricultural soils are a major source of the potent greenhouse gas and ozone depleting substance, N₂O. To implement management practices that minimize microbial N₂O production and maximize its consumption (i.e., complete denitrification), we must understand the interplay between simultaneously occurring biological and physical processes, especially how this changes with soil depth. Meaningfully disentangling of these processes is challenging and typical N₂O flux measurement techniques provide little insight into subsurface mechanisms. In addition, denitrification studies are often conducted on sieved soil in altered O₂ environments which relate poorly to in situ field conditions. Here, we developed a novel incubation system with headspaces both above and below the soil cores and field-relevant O₂ concentrations to better represent in situ conditions. We incubated intact sandy clay loam textured agricultural topsoil (0–10 cm) and subsoil (50–60 cm) cores for 3–4 days at 50% and 70% water-filled pore space, respectively. ¹⁵N-N₂O pool dilution and an SF₆ tracer were injected below the cores to determine the relative diffusivity and the net N₂O emission and gross N₂O emission and consumption fluxes. The relationship between calculated fluxes from the below and above soil core headspaces confirmed that the system performed well. Relative diffusivity did not vary with depth, likely due to the preservation of preferential flow pathways in the intact cores. Gross N₂O emission and uptake also did not differ with depth but were higher in the drier cores, contrary to expectation. We speculate this was due to aerobic denitrification being the primary N₂O consuming process and simultaneously occurring denitrification and nitrification both producing N₂O in the drier cores. We provide further evidence of substantial N₂O consumption in drier soil but without net negative N₂O emissions. The results from this study are important for the future application of the ¹⁵N-N₂O pool dilution method and N budgeting and modelling, as required for improving management to minimize N₂O losses.

中文翻译：

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分离不同水分含量和深度的完整农业土壤芯中的 N2O 生产和消耗

农业土壤是强效温室气体和消耗臭氧层物质 N ₂ O 的主要来源。要实施最大限度减少微生物 N ₂ O 产量并最大限度提高其消耗（即完全反硝化作用）的管理实践，我们必须了解同时发生的土壤之间的相互作用生物和物理过程，尤其是随着土壤深度的变化。有意义地解开这些过程具有挑战性，典型的 N ₂ O 通量测量技术几乎无法深入了解地下机制。此外，反硝化研究通常在 O _{2环境改变后的筛分土壤上进行，这与}原位关系不大现场条件。在这里，我们开发了一种新型孵化系统，其顶部空间位于土壤核心上方和下方，并具有与田间相关的 O ₂浓度，以更好地代表原位条件。我们分别在 50% 和 70% 的充满水的孔隙空间下，将完整的砂质粘壤土质地的农业表层土（0-10 厘米）和底土（50-60 厘米）核心培养 3-4 天。^将15 N-N ₂ O 池稀释液和 SF ₆示踪剂注入岩心下方，以确定相对扩散率和净 N ₂ O 排放量和总 N ₂O排放和消耗通量。土壤核心顶部空间下方和上方的计算通量之间的关系证实该系统运行良好。相对扩散率不随深度变化，这可能是由于在完整岩心中保留了优先流路。与预期相反，总 N ₂ O 排放量和吸收量也没有随深度而变化，但在较干燥的岩心中更高。我们推测这是由于好氧反硝化是主要的 N ₂ O 消耗过程并且同时发生的反硝化和硝化都在干燥器核心中产生 N _{2 O。}我们提供了进一步的证据，表明干燥土壤中大量 N ₂ O 消耗但没有净负 N ₂O排放。这项研究的结果对于¹⁵ N-N ₂ O 池稀释方法和 N 预算和建模的未来应用很重要，因为需要改进管理以最大限度地减少 N ₂ O 损失。