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Isotope fractionation factors controlling isotopocule signatures of soil‐emitted N 2 O produced by denitrification processes of various rates
Author(s) -
LewickaSzczebak Dominika,
Well Reinhard,
Bol Roland,
Gregory Andrew S.,
Matthews G. Peter,
Misselbrook Tom,
Whalley W. Richard,
Cardenas Laura M.
Publication year - 2014
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7102
Subject(s) - denitrification , chemistry , isotope fractionation , isotope , fractionation , isotope ratio mass spectrometry , isotopes of nitrogen , anoxic waters , environmental chemistry , stable isotope ratio , mass independent fractionation , δ18o , atmosphere (unit) , oxygen isotope ratio cycle , isotope analysis , isotopic signature , nitrogen , mass spectrometry , ecology , chromatography , physics , organic chemistry , quantum mechanics , biology , thermodynamics
RATIONALE This study aimed (i) to determine the isotopic fractionation factors associated with N 2 O 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 N 2 O production and reduction occurred simultaneously. METHODS Soil incubations were performed under a He/O 2 atmosphere and the denitrification product ratio [N 2 O/(N 2 + N 2 O)] was determined by direct measurement of N 2 and N 2 O fluxes. N 2 O isotopocules were analyzed by mass spectrometry to determine δ 18 O, δ 15 N and 15 N site preference within the linear N 2 O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N 2 O 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 N 2 O production and denitrification rates. For N 2 O 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 N 2 O reduction processes (i.e., higher than 2), are not valid for all conditions. Copyright © 2014 John Wiley & Sons, Ltd.