Institute of Plant Nutrition and Soil Science, Kiel University, Hermann-Rodewald-Str. 2, D-24118, Kiel, Germany.
Rapid Commun Mass Spectrom. 2013 Nov 15;27(21):2363-73. doi: 10.1002/rcm.6699.
N2O isotopomer ratios may provide a useful tool for studying N2O source processes in soils and may also help estimating N2O reduction to N2. However, remaining uncertainties about different processes and their characteristic isotope effects still hamper its application. We conducted two laboratory incubation experiments (i) to compare the denitrification potential and N2O/(N2O+N2) product ratio of denitrification of various soil types from Northern Germany, and (ii) to investigate the effect of N2O reduction on the intramolecular (15)N distribution of emitted N2O.
Three contrasting soils (clay, loamy, and sandy soil) were amended with nitrate solution and incubated under N2 -free He atmosphere in a fully automated incubation system over 9 or 28 days in two experiments. N2O, N2, and CO2 release was quantified by online gas chromatography. In addition, the N2O isotopomer ratios were determined by isotope-ratio mass spectrometry (IRMS) and the net enrichment factors of the (15)N site preference (SP) of the N2O-to-N2 reduction step (η(SP)) were estimated using a Rayleigh model.
The total denitrification rate was highest in clay soil and lowest in sandy soil. Surprisingly, the N2O/(N2O+N2) product ratio in clay and loam soil was identical; however, it was significantly lower in sandy soil. The IRMS measurements revealed highest N2O SP values in clay soil and lowest SP values in sandy soil. The η(SP) values of N2O reduction were between -8.2 and -6.1‰, and a significant relationship between δ(18)O and SP values was found.
Both experiments showed that the N2O/(N2O+N2) product ratio of denitrification is not solely controlled by the available carbon content of the soil or by the denitrification rate. Differences in N2O SP values could not be explained by variations in N2O reduction between soils, but rather originate from other processes involved in denitrification. The linear δ(18)O vs SP relationship may be indicative for N2O reduction; however, it deviates significantly from the findings of previous studies.
N2O 同位素比值可为研究土壤中 N2O 的源过程提供一种有用的工具，也有助于估算 N2O 还原为 N2。然而，不同过程及其特征同位素效应方面的剩余不确定性仍然阻碍了其应用。我们进行了两项实验室培养实验：（i）比较来自德国北部的各种土壤类型的反硝化潜力和反硝化生成的 N2O/(N2O+N2)产物比，以及（ii）研究 N2O 还原对排放的 N2O 中分子内（15）N 分布的影响。
在两项实验中，将三种对照土壤（粘土、壤土和沙土）用硝酸盐溶液处理并用氮气自由氦气气氛在全自动培养系统中培养 9 或 28 天。通过在线气相色谱定量测定 N2O、N2 和 CO2 的释放。此外，通过同位素比质谱法（IRMS）测定 N2O 同位素比值，并使用瑞利模型估算 N2O 到 N2 还原步骤的净（15）N 位偏好（SP）富集因子（η（SP））。
粘土土壤中的总反硝化速率最高，沙土土壤中的总反硝化速率最低。令人惊讶的是，粘土和壤土土壤中的 N2O/(N2O+N2)产物比相同；然而，沙土土壤中的产物比明显较低。IRMS 测量结果显示，粘土土壤中的 N2O SP 值最高，沙土土壤中的 SP 值最低。N2O 还原的 η（SP）值在-8.2 到-6.1‰之间，并且发现 δ（18）O 与 SP 值之间存在显著关系。
两项实验均表明，反硝化生成的 N2O/(N2O+N2)产物比不仅受土壤中可用碳含量或反硝化速率的控制。土壤之间 N2O SP 值的差异不能用土壤中 N2O 还原的变化来解释，而是源于反硝化过程中的其他过程。线性 δ（18）O 与 SP 关系可能指示 N2O 还原；然而，它与先前研究的结果有很大差异。
