Button Erik S, Marsden Karina A, Nightingale Philip D, Dixon Elizabeth R, Chadwick David R, Jones David L, Cárdenas Laura M
School of Natural Sciences Bangor University Bangor Gwynedd UK.
Plymouth Marine Laboratory, Prospect Pl, Marine Biogeochemical Observations Plymouth Devon UK.
Eur J Soil Sci. 2023 Mar-Apr;74(2):e13363. doi: 10.1111/ejss.13363. Epub 2023 Apr 27.
Agricultural soils are a major source of the potent greenhouse gas and ozone depleting substance, NO. To implement management practices that minimize microbial NO 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 NO flux measurement techniques provide little insight into subsurface mechanisms. In addition, denitrification studies are often conducted on sieved soil in altered O environments which relate poorly to field conditions. Here, we developed a novel incubation system with headspaces both above and below the soil cores and field-relevant O concentrations to better represent 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. N-NO pool dilution and an SF tracer were injected below the cores to determine the relative diffusivity and the net NO emission and gross NO 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 NO 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 NO consuming process and simultaneously occurring denitrification and nitrification both producing NO in the drier cores. We provide further evidence of substantial NO consumption in drier soil but without net negative NO emissions. The results from this study are important for the future application of the N-NO pool dilution method and N budgeting and modelling, as required for improving management to minimize NO losses.
农业土壤是强效温室气体和臭氧层消耗物质一氧化氮（NO）的主要来源。要实施能将微生物NO生成量降至最低并使其消耗量最大化（即完全反硝化作用）的管理措施，我们必须了解同时发生的生物和物理过程之间的相互作用，尤其是这一相互作用如何随土壤深度而变化。有意义地厘清这些过程具有挑战性，而典型的NO通量测量技术对地下机制的洞察有限。此外，反硝化作用研究通常在经过筛分的土壤中进行，且氧环境有所改变，这与田间条件相关性较差。在此，我们开发了一种新型培养系统，该系统在土壤柱体的上方和下方均设有顶空，并设置与田间相关的氧浓度，以便更好地模拟实际条件。我们分别在50%和70%的充水孔隙空间条件下，将质地为砂质粘壤土的完整农业表土（0 - 10厘米）和底土（50 - 60厘米）柱体培养3 - 4天。在柱体下方注入N - NO库稀释液和一种SF示踪剂，以确定相对扩散率以及净NO排放量、总NO排放和消耗通量。来自土壤柱体下方和上方顶空的计算通量之间的关系证实该系统运行良好。相对扩散率并未随深度变化，这可能是由于完整柱体中优先流路得以保留。总NO排放量和吸收量也未随深度而有所不同，但在较干燥的柱体中更高，这与预期相反。我们推测这是因为好氧反硝化作用是主要的NO消耗过程，且在较干燥的柱体中同时发生的反硝化作用和硝化作用都会产生NO。我们进一步证明了在较干燥土壤中存在大量的NO消耗，但没有净负NO排放。本研究结果对于未来N - NO库稀释法的应用以及氮预算和建模具有重要意义，这是改善管理以尽量减少NO损失所必需的。
