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N 2 O source partitioning in soils using 15 N site preference values corrected for the N 2 O reduction effect
Author(s) -
Wu Di,
Köster Jan Reent,
Cárdenas Laura M.,
Brüggemann Nicolas,
LewickaSzczebak Dominika,
Bol Roland
Publication year - 2016
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.7493
Subject(s) - chemistry , denitrification , soil water , fractionation , isotope , stable isotope ratio , nitrous oxide , nitrification , atmosphere (unit) , analytical chemistry (journal) , nitrogen , environmental chemistry , soil science , chromatography , thermodynamics , environmental science , physics , organic chemistry , quantum mechanics
Rationale The aim of this study was to determine the impact of isotope fractionation associated with N 2 O reduction during soil denitrification on N 2 O site preference (SP) values and hence quantify the potential bias on SP‐based N 2 O source partitioning. Methods The N 2 O SP values ( n = 431) were derived from six soil incubation studies in N 2 ‐free atmosphere, and determined by isotope ratio mass spectrometry (IRMS). The N 2 and N 2 O concentrations were measured directly by gas chromatography. Net isotope effects (NIE) during N 2 O reduction to N 2 were compensated for using three different approaches: a closed‐system model, an open‐system model and a dynamic apparent NIE function. The resulting SP values were used for N 2 O source partitioning based on a two end‐member isotopic mass balance. Results The average SP 0 value, i.e. the average SP values of N 2 O prior to N 2 O reduction, was recalculated with the closed‐system model, resulting in −2.6 ‰ (±9.5), while the open‐system model and the dynamic apparent NIE model gave average SP 0 values of 2.9 ‰ (±6.3) and 1.7 ‰ (±6.3), respectively. The average source contribution of N 2 O from nitrification/fungal denitrification was 18.7% (±21.0) according to the closed‐system model, while the open‐system model and the dynamic apparent NIE function resulted in values of 31.0% (±14.0) and 28.3% (±14.0), respectively. Conclusions Using a closed‐system model with a fixed SP isotope effect may significantly overestimate the N 2 O reduction effect on SP values, especially when N 2 O reduction rates are high. This is probably due to soil inhomogeneity and can be compensated for by the application of a dynamic apparent NIE function, which takes the variable reduction rates in soil micropores into account. Copyright © 2016 John Wiley & Sons, Ltd.