Liming acidic soils is often found to reduce their N2O emission due to lowered N2O/(N2O + N2) product ratio of denitrification. Some field experiments have shown the opposite effect, however, and the reason for this could be that liming stimulates nitrification-driven N2O production by enhancing nitrification rates, and by favoring ammonia oxidizing bacteria (AOB) over ammonia oxidizing archaea (AOA). AOB produce more N2O than AOA, and high nitrification rates induce transient/local hypoxia, thereby stimulating heterotrophic denitrification. To study these phenomena, we investigated nitrification and denitrification kinetics and the abundance of AOB and AOA in soils sampled from a field experiment 2–3 years after liming. The field trial compared traditional liming (carbonates) with powdered siliceous rocks. As expected, the N2O/(N2O + N2) product ratio of heterotrophic denitrification declined with increasing pH, and the potential nitrification rate and its N2O yield (YN2O: N2O-N/NO3–-N), as measured in fully oxic soil slurries, increased with pH, and both correlated strongly with the AOB/AOA gene abundance ratio. Soil microcosm experiments were monitored for nitrification, its O2-consumption and N2O emissions, as induced by ammonium fertilization. Here we observed a conspicuous dependency on water filled pore space (WFPS): at 60 and 70% WFPS, YN2O was 0.03-0.06% and 0.06–0.15%, respectively, increasing with increasing pH, as in the aerobic soil slurries. At 85% WFPS, however, YN2O was more than two orders of magnitude higher, and decreased with increasing pH. A plausible interpretation is that O2 consumption by fertilizer-induced nitrification cause hypoxia in wet soils, hence induce heterotrophic nitrification, whose YN2O decline with increasing pH. We conclude that while low emissions from nitrification in well-drained soils may be enhanced by liming, the spikes of high N2O emission induced by ammonium fertilization at high soil moisture may be reduced by liming, because the heterotrophic N2O reduction is enhanced by high pH.

中文翻译：

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石灰对自养硝化驱动的 N2O 排放的偶然影响

由于反硝化的 N2O/(N2O + N2) 产物比降低，通常发现石灰酸性土壤会减少其 N2O 排放。然而，一些现场实验显示出相反的效果，其原因可能是石灰通过提高硝化速率和有利于氨氧化细菌 (AOB) 而不是氨氧化古细菌 (AOA)，从而刺激了硝化驱动的 N2O 生产。AOB 产生的 N2O 比 AOA 多，高硝化率会导致瞬时/局部缺氧，从而刺激异养反硝化。为了研究这些现象，我们研究了在石灰后 2-3 年的田间试验中取样的土壤中的硝化和反硝化动力学以及 AOB 和 AOA 的丰度。现场试验将传统石灰（碳酸盐）与粉状硅质岩进行了比较。正如预期的那样，异养反硝化的 N2O/(N2O + N2) 产物比随着 pH 值的增加而下降，潜在硝化速率及其 N2O 产量（YN2O：N2O-N/NO3–-N），如在完全好氧的土壤泥浆中测量的，随着pH，两者都与 AOB/AOA 基因丰度比密切相关。监测土壤微观实验的硝化作用、其 O2 消耗和 N2O 排放，如由铵肥引起的。在这里，我们观察到对充满水的孔隙空间 (WFPS) 的显着依赖性：在 60% 和 70% 的 WFPS 下，YN2O 分别为 0.03-0.06% 和 0.06-0.15%，随着 pH 值的增加而增加，就像在好氧土壤浆中一样。然而，在 85% 的 WFPS 下，YN2O 高出两个数量级以上，并且随着 pH 值的增加而降低。一个合理的解释是肥料诱导的硝化作用消耗 O2 导致湿土壤缺氧，从而诱导异养硝化作用，其 YN2O 随 pH 增加而下降。我们得出的结论是，虽然在排水良好的土壤中硝化作用的低排放可能会因施石灰而增加，但在高土壤湿度下施铵肥引起的高 N2O 排放峰值可能会因施石灰而降低，因为高 pH 值会增强异养 N2O 的减少。