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Isotopologue fractionation during N 2 O production by fungal denitrification
Author(s) -
Sutka Robin L.,
Adams Gerard C.,
Ostrom Nathaniel E.,
Ostrom Peggy H.
Publication year - 2008
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.3820
Subject(s) - chemistry , denitrification , isotopologue , nitrite , fractionation , nitrate , isotopes of nitrogen , environmental chemistry , nitrous oxide , nitrogen , isotope , stable isotope ratio , chromatography , organic chemistry , physics , quantum mechanics , molecule
Identifying the importance of fungi to nitrous oxide (N 2 O) production requires a non‐intrusive method for differentiating between fungal and bacterial N 2 O production such as natural abundance stable isotopes. We compare the isotopologue composition of N 2 O produced during nitrite reduction by the fungal denitrifiers Fusarium oxysporum and Cylindrocarpon tonkinen s e with published data for N 2 O production during bacterial nitrification and denitrification. The fractionation factors for bulk nitrogen isotope values for fungal denitrification were in the range −74.7 to −6.6‰. There was an inverse relationship between the absolute value of the fractionation factors and the reaction rate constant. We interpret this in terms of variation in the relative importance of the rate constants for diffusion and enzymatic reduction in controlling the net isotope effect for N 2 O production during fungal denitrification. Over the course of nitrite reduction, the δ 18 O values for N 2 O remained constant and did not exhibit a relationship with the concentration characteristic of an isotope effect. This probably reflects isotopic exchange with water. Similar to the δ 18 O data, the site preference (SP; the difference in δ 15 N between the central and outer N atoms in N 2 O) was unrelated to concentration during nitrite reduction and, therefore, has the potential to act as a conservative tracer of production from fungal denitrification. The SP values of N 2 O produced by F. oxysporum and C. tonkinense were 37.1 ± 2.5‰ and 36.9 ± 2.8‰, respectively. These SP values are similar to those obtained in pure culture studies of bacterial nitrification but quite distinct from SP values for bacterial denitrification. The large magnitude of the bulk nitrogen isotope fractionation and the δ 18 O values associated with fungal denitrification are distinct from bacterial production pathways; thus multiple isotopologue data holds much promise for resolving bacterial and fungal production. Our work further provides insight into the role that fungal and bacterial nitric oxide reductases have in determining site preference during N 2 O production. Copyright © 2008 John Wiley & Sons, Ltd.