Canadian Forest Service Publications

Soil denitrification fluxes from three northeastern North American forests across a range of nitrogen deposition. 2015. Morse, J.L.; Durîn, J.; Beall, F.; Enanga, E.M.; Creed, I.F.; Fernandez, I.; Groffman, P.M. Oecologia 177:17-27.

Year: 2015

Issued by: Great Lakes Forestry Centre

Catalog ID: 36568

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1007/a00442-014-3117-1

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Abstract

In northern forests, large amounts of missing N that dominate N balances at scales ranging from small watersheds to large regional drainage basins may be related to N-gas production by soil microbes. We measured denitrification rates in forest soils in northeastern North America along a N deposition gradient to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We quantified N2 and N2O fluxes in the laboratory with an intact-core method and monitored soil O2, temperature and moisture in three forests differing in natural and anthropogenic N enrichment: Turkey Lakes Watershed, Ontario; Hubbard Brook Experimental Forest, New Hampshire; and Bear Brook Watershed, Maine (fertilized and reference plots in hardwood and softwood stands). Total N-gas flux estimates ranged from <1 in fertilized hardwood uplands at Bear Brook to >100 kg N ha−1 year−1 in hardwood wetlands at Turkey Lakes. N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates (Bear Brook < Hubbard Brook < Turkey Lakes) but did not increase in the site where N fertilizer has been added since 1989 (Bear Brook). Our results show that denitrification is an important and underestimated term (1–24 % of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition in this region.

Plain Language Summary

There is uncertainty about nitrogen (N)-gas fluxes, and N balances in forests, which is relevant to both air and water quality issues. We studied soil denitrification rates in three northeastern North American forests ranging in nitrogen (N) availability. We wanted to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We found that N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates but did not increase in the site where N fertilizer has been added. We show that denitrification is an important and underestimated term (1–24 % of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition.