Isotope fractionation factors controlling isotopocule signatures of soil-emitted N₂O produced by denitrification processes of various rates.
Isotope fractionation factors controlling isotopocule signatures of soil-emitted N₂O produced by denitrification processes of various rates.
复制标题
DOI：
10.1002/rcm.7102
复制
发表时间：
2015-02
期刊：
影响因子：
--
通讯作者：
D. Lewicka-Szczebak;R. Well;R. Bol;Andrew S. Gregory;G. P. Matthews;T. Misselbrook;W. R. Whalley
中科院分区：
文献类型：
--
作者：
D. Lewicka-Szczebak;R. Well;R. Bol;Andrew S. Gregory;G. P. Matthews;T. Misselbrook;W. R. Whalley
本研究的目的是(I)确定与土壤反硝化过程中N2O产生和减少相关的同位素分馏系数；(Ii)帮助确定控制同位素效应大小的因素。首次在含氧气氛下用一种同时产生和还原N2O的新方法测定了反硝化的同位素效应。方法在He/O2气氛下进行土壤培养，通过直接测量N_2和N_2O通量来确定反硝化产物比[N_2O/(N_2+N_2O)]。用质谱仪分析了δ(18)O、δ(15)N和(15)N在线性N2O分子(SP)中的位置择优。应用同位素模型同时测定了N2O产生和减少的净同位素效应(η)，同时考虑了两个不同土壤池的排放。结果N2O产生过程中的(15)N和(18)O同位素效应与反硝化速率之间存在明显的相关性。对于N2O的还原，不同产生率的两个不同的土壤库具有不同的同位素效应。对于适中的产品比率(从0.1到1.0)，先前研究给出的同位素效应范围得到了确认和改进，而对于非常低的产品比率(低于0.1)，净同位素影响要小得多。结论在氧气培养条件下测定的与反硝化作用相关的分级因子与以前在缺氧条件下测定的因子相似，因此可能适用于现场研究。然而，研究表明，以前被认为是典型的N2O还原过程的η(18)O/η(15)N比率(即高于2)并不适用于所有条件。
RATIONALE This study aimed (i) to determine the isotopic fractionation factors associated with N2O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N2O production and reduction occurred simultaneously. METHODS Soil incubations were performed under a He/O2 atmosphere and the denitrification product ratio [N2O/(N2 + N2O)] was determined by direct measurement of N2 and N2O fluxes. N2O isotopocules were analyzed by mass spectrometry to determine δ(18)O, δ(15)N and (15)N site preference within the linear N2O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N2O production and reduction, taking into account emissions from two distinct soil pools. RESULTS A clear relationship was observed between (15)N and (18)O isotope effects during N2O production and denitrification rates. For N2O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller. CONCLUSIONS The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η(18)O/η(15)N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions.