Well R, Flessa H
Johann Heinrich von Thünen-Institut, Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Agricultural Climate Research, Bundesallee 50, 38116 Braunschweig, Germany.
Rapid Commun Mass Spectrom. 2009 Sep;23(18):2996-3002. doi: 10.1002/rcm.4216.
Isotopic signatures can be used to study sink and source processes of N(2)O, but the success of this approach is limited by insufficient knowledge on the isotope fractionation factors of the various reaction pathways. We investigated isotope enrichment factors of the N(2)O-to-N(2) step of denitrification (epsilon) in two arable soils, a silt-loam Haplic Luvisol and a sandy Gleyic Podzol. In addition to the epsilon of (18)O (epsilon(18O)) and of average (15)N (epsilon(bulk)), the epsilon of the (15)N site preference within the linear N(2)O molecule (epsilon(SP)) was also determined. Soils were anaerobically incubated in gas-tight bottles with N(2)O added to the headspace to induce N(2)O reduction. Pre-treatment included the removal of NO(3) (-) to prevent N(2)O production. Gas samples were collected regularly to determine the dynamics of N(2)O reduction, the time course of the isotopic signatures of residual N(2)O, and the associated isotope enrichment factors. To vary reduction rates and associated fractionation factors, several treatments were established including two levels of initial N(2)O concentration and anaerobic pre-incubation with or without addition of N(2)O. N(2)O reduction rates were affected by the soil type and initial N(2)O concentration. The epsilon(18O) and epsilon(bulk) ranged between -13 and -20 per thousand, and between -5 and -9 per thousand, respectively. Both quantities were more negative in the Gleyic Podzol. The epsilon of the central N position (epsilon(alpha)) was always larger than that of the peripheral N-position (epsilon(beta)), giving epsilon(SP) of -4 to -8 per thousand. The ranges and variation patterns of epsilon were comparable with those from previous static incubation studies with soils. Moreover, we found a relatively constant ratio between epsilon(18O) and epsilon(bulk) which is close to the default ratio of 2.5 that had been previously suggested. The fact that different soils exhibited comparable epsilon under certain conditions suggests that these values could serve to identify N(2)O reduction from the isotopic fingerprints of N(2)O emitted from any soil.
同位素特征可用于研究N₂O的汇和源过程，但该方法的成功受到对各种反应途径的同位素分馏因子认识不足的限制。我们研究了两种耕地土壤（粉质壤土简育淋溶土和砂质潜育灰壤）中反硝化作用从N₂O到N₂步骤的同位素富集因子（ε）。除了¹⁸O的ε（ε₁₈O）和平均¹⁵N的ε（ε bulk）外，还测定了线性N₂O分子内¹⁵N位点偏好的ε（εSP）。将土壤在气密瓶中进行厌氧培养，向顶空加入N₂O以诱导N₂O还原。预处理包括去除NO₃⁻以防止N₂O产生。定期采集气体样品以确定N₂O还原的动力学、残留N₂O同位素特征的时间进程以及相关的同位素富集因子。为了改变还原速率和相关的分馏因子，建立了几种处理方法，包括两个初始N₂O浓度水平以及有无添加N₂O的厌氧预培养。N₂O还原速率受土壤类型和初始N₂O浓度的影响。ε₁₈O和ε bulk分别在-13‰至-20‰和-5‰至-9‰之间。在潜育灰壤中这两个量更负。中心N位置的ε（εα）总是大于外围N位置的ε（εβ），εSP为-4‰至-8‰。ε的范围和变化模式与先前土壤静态培养研究的结果相当。此外，我们发现ε₁₈O和ε bulk之间的比例相对恒定，接近先前建议的默认比例2.5。在某些条件下不同土壤表现出可比的ε这一事实表明，这些值可用于从任何土壤排放的N₂O的同位素指纹中识别N₂O还原。
