Quantifying N2O reduction to N2 based on N2O isotopocules - validation with independent methods (helium incubation and 15N gas flux method)
Quantifying N2O reduction to N2 based on N2O isotopocules - validation with independent methods (helium incubation and 15N gas flux method)
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DOI：
10.5194/bg-14-711-2017
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发表时间：
2017-02-14
期刊：
影响因子：
4.9
通讯作者：
Well, Reinhard
中科院分区：
文献类型：
--
作者：
Lewicka-Szczebak, Dominika;Augustin, Juergen;Well, Reinhard
土壤排放N2 O的稳定同位素分析（δ N-15（散装），δ O-18和δ N-15（sp）= N-15的线性N2 O分子内的位置偏好）可能有助于量化N2 O还原为N-2，一个重要的，但很少量化的过程中，土壤氮循环。N2 O残留分数（剩余未还原N2 O，rN（2）O）可以从残余N2 O的测量的同位素富集理论上计算。然而，不同的N2 O产生途径也可能影响N2 O同位素特征，从而使这种同位素分馏方法的应用变得复杂，在这里，基于两种不同土壤类型的实验室土壤培养，应用两种参考方法来定量rN（2）O：氦培养直接测量N-2通量和N-15气体通量法。这允许将测量的rN（2）O值与基于残留N2 O的同位素富集计算的rN（2）O值进行比较。结果表明，N_2O同位素分馏方法的性能与伴随的N_2O和N-2源过程有关，最关键的是确定还原前N_2O的初始同位素特征（δ（0））。我们表明，如果在时间上稳定，则delta（0）可以通过实验很好地确定，然后成功地应用于基于delta N-15（sp）值的rN（2）O的测定。要处理的更成问题的是delta（0）值的时间变化导致仅基于delta N-15（sp）值的方法失败。对于这种情况下，我们在这里提出了一个双N2 O同位素映射方法，其中计算是基于之间的关系Δ O-18和Δ N-15（SP）值。这允许同时估计N2 O产生途径的贡献和rN（2）O值。
Stable isotopic analyses of soil-emitted N2O (delta N-15(bulk), delta O-18 and delta N-15(sp) = N-15 site preference within the linear N2O molecule) may help to quantify N2O reduction to N-2, an important but rarely quantified process in the soil nitrogen cycle. The N2O residual fraction (remaining unreduced N2O, rN(2)O / can be theoretically calculated from the measured isotopic enrichment of the residual N2O. However, various N2O- producing pathways may also influence the N2O isotopic signatures, and hence complicate the application of this isotopic fractionation approach.Here this approach was tested based on laboratory soil incubations with two different soil types, applying two reference methods for quantification of rN(2)O: helium incubation with direct measurement of N-2 flux and the N-15 gas flux method. This allowed a comparison of the measured rN(2)O values with the ones calculated based on isotopic enrichment of residual N2O. The results indicate that the performance of the N2O isotopic fractionation approach is related to the accompanying N2O and N-2 source processes and the most critical is the determination of the initial isotopic signature of N2O before reduction (delta(0)). We show that delta(0) can be well determined experimentally if stable in time and then successfully applied for determination of rN(2)O based on delta N-15(sp) values. Much more problematic to deal with are temporal changes of delta(0) values leading to failure of the approach based on delta N-15(sp) values only. For this case, we propose here a dual N2O isotopocule mapping approach, where calculations are based on the relation between delta O-18 and delta N-15(sp) values. This allows for the simultaneous estimation of the N2O-producing pathways' contribution and the rN(2)O value.