Rapid conversion of added nitrate to nitrous oxide and dinitrogen in northern forest soil

TitleRapid conversion of added nitrate to nitrous oxide and dinitrogen in northern forest soil
Publication TypeJournal Article
Year of Publication2016
AuthorsKulkarni, MV, Yavitt, JB, Groffman, PM
JournalGeomicrobiology Journal
Pagination00 - 00
Date Published2016/10/03/
ISBN Number0149-0451

Our aim was to simulate wet deposition of atmospheric nitrate (NO3−) onto forest soils and trace its fate via conversion spatially and temporally into gaseous products nitrous oxide (N2O) and dinitrogen (N2). The most likely mechanism is microbial denitrification, but an intermediate product nitrite (NO2−) can fuel N2O production via a chemical pathway involving reactions with iron and / or organic matter referred to as chemodenitrification. During summer months, we applied tracer amounts of 15N-labelled NO3− onto forest soils (pH ∼4) at three sites in the White Mountain region of New Hampshire, USA. We recovered 15N as N2O in 210 of 504 measurements (42%) versus 15N as N2 in 51 of 504 measurements (10%), suggesting partial microbial denitrification and / or chemodenitrification. When recovery occurred, the mean percent recovery of added 15N was just 1.1% as N2O, although N2 recovery was 33%. A site with old-growth trees had a larger percentage recovery as N2 (48%), whereas a site that had burned 100-years ago had a small percentage recovery as N2O (0.24%). The 15N composition of N2O in ambient air, collected before addition of the label, was markedly enriched in 15N. Since flux measurements were made two hours after the addition, the results suggest that denitrification enzymes and conditions for chemodenitrification are present throughout the summer months but account for small amounts of NO3− conversion into N2O and N2.