Experimental determinations of isotopic fractionation factors associated with N2O production and reduction during denitrification in soils
Experimental determinations of isotopic fractionation factors associated with N2O production and reduction during denitrification in soils
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DOI：
10.1016/j.gca.2014.03.010
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发表时间：
2014-06-01
影响因子：
5
通讯作者：
Flessa, Heiner
中科院分区：
文献类型：
--
作者：
Lewicka-Szczebak, Dominika;Well, Reinhard;Flessa, Heiner
量化可耕地土壤中的反硝化作用对于预测氮肥损失和N2 O排放至关重要。稳定同位素分析排放的N2 O（δ N-15，δ O-18和SP = N-15的线性N2 O分子内的网站偏好）可能有助于区分生产途径和量化N2 O还原为N-2。然而，由于对同位素分馏机制的认识不足，这种解释往往是模糊的。在这里，我们提出了一个复杂的实验方法来确定与反硝化作用的净分馏因子（eta）。这一决定是基于三个实验室实验不同的实验设置和土壤性质。比较了静态和动态孵育技术。使用了所有可用于独立测定N2 O还原贡献的方法，即无N-2气氛培养、乙炔抑制技术和N-15气体通量法。对于N2 O生产：（i）土壤水和产生的N2 O之间确定的Δ O-18差异从+18/1000到+18/1000不等。42 ppm，与土壤含水饱和度呈极严格的负相关;（ii）所测定的N2 O产生量的eta N-15由千分之-55至─ 38份每千和分馏降低基板的可用性;（iii）所确定的SP产生的N2 O变化从-3份每千到+9份每千。减少N2 O：（i）测定的N2 O还原的η O-18和η N-15分别在-18ppm至+4ppm和-11ppm至+12ppm的很宽范围内变化，并且在很大程度上取决于实验设置的差异;而（ii）测定的N2 O还原的η SP显示出与所有先前研究非常一致的值，并且在从千分之-2到千分之-8的相当窄的范围内变化。可以得出结论，在实验室培养过程中确定的N2 O生产的eta值仅粗略估计在实地研究条件下预期的相应值。与N2 O还原相关的η O-18和η N-15可能变化很大，可能取决于N2 O产生和还原的空间和时间重合，因此在自然条件下尚不能预测。然而，N2 O还原的eta SP似乎是相对稳健的，并且基于土壤排放的N2 O的SP，可以使用约千分之-5的最可能值来限制N2 O还原。(C)2014爱思唯尔有限公司版权所有。
Quantifying denitrification in arable soils is crucial in predicting nitrogen fertiliser losses and N2O emissions. Stable isotopologue analyses of emitted N2O (delta N-15, delta O-18 and SP = N-15 site preference within the linear N2O molecule) may help to distinguish production pathways and to quantify N2O reduction to N-2. However, such interpretations are often ambiguous due to insufficient knowledge on isotopic fractionation mechanisms. Here we present a complex experimental approach to determine the net fractionation factors (eta) associated with denitrification. This determination is based on three laboratory experiments differing in their experimental set-up and soil properties. Static and dynamic incubation techniques were compared. All available methods for independent determination of N2O reduction contribution were used, namely, N-2-free atmosphere incubation, acetylene inhibition technique and N-15 gas-flux method.For N2O production: (i) the determined difference in delta O-18 between soil water and produced N2O vary from +18 parts per thousand to +42 parts per thousand and show very strict negative correlation with soil water saturation; (ii) the determined eta N-15 of N2O production vary from -55 parts per thousand to -38 parts per thousand and the fractionation decreases with decreasing substrate availability; (iii) the determined SP of produced N2O vary from -3 parts per thousand to +9 parts per thousand. For N2O reduction: (i) the determined eta O-18 and eta N-15 of N2O reduction vary in very wide ranges from -18 parts per thousand to +4 parts per thousand and from -11 parts per thousand to +12 parts per thousand, respectively, and depend largely on the differences in experimental setups; whereas (ii) the determined eta SP of N2O reduction shows a very consistent value with all previous studies and varies in a rather narrow range from -2 parts per thousand to -8 parts per thousand. It can be concluded that eta values of N2O production determined during laboratory incubations yield only roughly estimates for respective values expectable under field study conditions. eta O-18 and eta N-15 associated with N2O reduction may vary largely, probably depending on spatial and temporal coincidence of N2O production and reduction, and are hence not yet predictable for natural conditions. However, the eta SP of N2O reduction appeared to be relatively robust and a most probable value of about -5 parts per thousand can be used to constrain N2O reduction based on SP of soil emitted N2O. (C) 2014 Elsevier Ltd. All rights reserved.