Nitrification and denitrification are known to co-occur in soils, but the effect of fertilisation history on N₂O fluxes and the relative source partitioning of the N₂O has not been thoroughly investigated. In this study, we therefore combined a high-tech ¹⁵N stable isotope tracing technique with quantitative PCR (qPCR) to explore the relative contributions of nitrification and denitrification to N₂O production by a sandy-loam Eutric Cambisol soil treated repeatedly with ammonium sulfate [(NH₄)₂SO₄] or potassium nitrate (KNO₃) for 3 years prior. Both soils (historically (NH₄)₂SO₄ and historically KNO₃ treated) were amended separately with (¹⁵NH₄)₂SO₄ and K¹⁵NO₃ and incubated at 80% water filled pore space for 30 days. Soil N₂O emissions, NH₄⁺ and NO₃⁻ concentrations and their corresponding ¹⁵N-enrichments were determined. The effect of N addition on N transformation rates was also calculated. The total abundance of nitrifiers was estimated by qPCR of the amoA gene from bacteria and archaea, and that of denitrifiers by using the nirK, nirS, norB and nosZI genes as molecular targets. In the historically (NH₄)₂SO₄-treated soil, 49.0–58.0% of the N₂O emitted originated from nitrification and 42.0–51.0% from denitrification during incubation. The production of N₂O was accompanied by a decrease in soil NH₄⁺ concentrations and a parallel increase in the concentration of soil NO₃⁻. In addition, the abundance of the bacterial and archaeal amoA gene increased during the incubation. Conversely, in the soil historically treated with KNO₃, the ¹⁵N isotopic analyses showed that denitrification contributed 84.0–99.0% of the total N₂O produced. Decreases in soil NO₃⁻ concentrations paralleled the increase in ¹⁵N enrichment of N₂O and the abundance of the nirK, nirS, norB and nosZI genes. The results also showed that values of ¹⁵N₂ enrichment were significantly higher in the KNO₃-treated soil, which is in line with the higher abundance of the nosZI gene. Calculation of the N transformation rates indicated that autotrophic nitrification and denitrification were responsible for N₂O production in the historically (NH₄)₂SO₄-treated soil and that denitrification was the most important N₂O source in the soil treated with KNO₃. We conclude that N-fertilisation history, and not simply soil oxygen availability, affect the relative contributions of nitrification and denitrification to soil N₂O emissions. Indeed, here we have shown that nitrification can be an important N₂O source process even in soils maintained at high moisture contents.

硝化和反硝化已知共同出现在土壤中，但历史受精的N个效果₂ Ó通量和N的相对源分区₂ O具有尚未彻底调查。因此，在这项研究中，我们将高科技¹⁵ N稳定同位素示踪技术与定量PCR（qPCR）相结合，以探索硝化和反硝化作用对沙壤土Eutric Cambisol土壤反复进行硫酸铵处理而产生的N ₂ O的相对贡献。[（NH ₄）₂ SO ₄ ]或硝酸钾（KNO ₃）需使用3年。两种土壤（历史上（NH ₄）₂ SO分别用（¹⁵ NH ₄）₂ SO ₄和K ¹⁵ NO ₃修正₄和以前处理过的KNO ₃），并在充满水的80％孔隙空间中孵育30天。土壤氮素_2个O排放，NH ₄ ⁺和NO ₃ ^-的浓度和它们的相应¹⁵的N-富集进行了测定。还计算了氮添加对氮转化率的影响。通过qPCR对来自细菌和古细菌的amoA基因进行定量PCR ，并通过使用nirK对反硝化剂进行分析，以估算硝化剂的总丰度，nirS，norB和nosZ I基因作为分子靶标。在历史上（NH ₄）₂ SO ₄处理过的土壤中，孵化期间排放的N ₂ O的49.0-58.0％来自硝化，而42.0-51.0％则来自反硝化。制造N-的₂ O的伴随着在土壤中的降低NH _4个⁺浓度和在土壤中NO的浓度的增加平行₃ ^- 。另外，在孵育过程中细菌和古细菌amoA基因的丰度增加。相反，在经过KNO ₃处理的土壤中，¹⁵N同位素分析表明，反硝化作用占N ₂ O产生总量的84.0–99.0％。减少在土壤中NO ₃ ^-的浓度在平行的增加¹⁵ N中的Ñ富集₂ O与丰度nirK，NIRS，NORB和nosZ我的基因。结果还表明，在KNO ₃处理的土壤中¹⁵ N ₂富集值显着更高，这与nosZ的丰度更高相符。我基因。N转化率的计算表明，自养硝化和反硝化是历史（NH ₄）₂ SO ₄处理过的土壤中N ₂ O产生的原因，而反硝化是用KNO ₃处理过的土壤中最重要的N ₂ O来源。。我们得出的结论是，氮肥的施用历史（而不仅仅是土壤中的氧气供应）会影响硝化和反硝化对土壤N ₂ O排放的相对贡献。的确，这里我们已经表明，硝化即使在保持高水分含量的土壤中也可以是重要的N ₂ O源过程。