Virginia Institute of Marine Science
Removal of excess nitrogen (N) can best be achieved through denitrification processes that transform N in water and terrestrial ecosystems to di-nitrogen (N-2) gas. The greenhouse gas nitrous oxide (N2O) is considered an intermediate or end-product in denitrification pathways. Both abiotic and biotic denitrification processes use a single N source to form N2O. However, N-2 can be formed from two distinct N sources (known as hybrid N-2) through biologically mediated processes of anammox and codenitrification. We questioned if hybrid N-2 produced during fungal incubation at neutral pH could be attributed to abiotic nitrosation and if N2O was consumed during N-2 formation. Experiments with gas chromatography indicated N-2 was formed in the presence of live and dead fungi and in the absence of fungi, while N2O steadily increased. We used isotope pairing techniques and confirmed abiotic production of hybrid N-2 under both anoxic and 20% O-2 atmosphere conditions. Our findings question the assumptions that (1) N2O is an intermediate required for N-2 formation, (2) production of N-2 and N2O requires anaerobiosis, and (3) hybrid N-2 is evidence of codenitrification and/ or anammox. The N cycle framework should include abiotic production of N-2.
NITRIC-OXIDE REDUCTASE; N2O PRODUCTION; CO-DENITRIFICATION; FUSARIUM-OXYSPORUM; OXIDIZING BACTERIA; ARABIAN SEA; SOIL; GAS; FRACTIONATION; GRASSLAND
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The authors thank the team at Landcare Research in New Zealand for supporting this idea. This work was partially funded by a USDA-NIFR grant [2014-67019-21614]; New Zealand's Ministry of Business Innovation and Employment, Royal Society of New Zealand International Travel Programme; and New Zealand Ecosystems and Global Change Fund. The authors are grateful to Veronica Rollinson, Sujatha Senanayake, Duckchul Park, and Megan Peterson for technical assistance and Bill Schlesinger, Iris Anderson, Neha Jha, Mikki Eken, and Leah Kearns for their comments, support and editorial reviews.
Phillips, Rebecca L.; Song, Bongkeun; McMillan, Andrew M. S.; Grelet, Gwen; Weir, Bevan S.; Palmada, Thilak; and Tobias, Craig, "Chemical formation of hybrid di-nitrogen calls fungal codenitrification into question" (2016). VIMS Articles. 23.