title: Soil denitrification fluxes from three northeastern North American forests across a range of nitrogen deposition.
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.
authors.affiliation: Cary Institute of Ecosystem Studies, Millbrook, NY, USA, jlmorse@pdx.edu.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Morse
authors.forename: Jorge
authors.initials: J
authors.lastname: Durán
authors.forename: Fred
authors.initials: F
authors.lastname: Beall
authors.forename: Eric M
authors.initials: EM
authors.lastname: Enanga
authors.forename: Irena F
authors.initials: IF
authors.lastname: Creed
authors.forename: Ivan
authors.initials: I
authors.lastname: Fernandez
authors.forename: Peter M
authors.initials: PM
authors.lastname: Groffman
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D000397:Air Pollution; D058440:Denitrification; D005308:Fertilizers; D065928:Forests; D008281:Maine; D009584:Nitrogen / Q000032:analysis*; D058458:Nitrogen Cycle; D009609:Nitrous Oxide / Q000032:analysis; D009864:Ontario; D012987:Soil / Q000737:chemistry*; D014197:Trees; D053833:Wetlands
chemical_list: D000393:Air Pollutants; D005308:Fertilizers; D012987:Soil; D009609:Nitrous Oxide; D009584:Nitrogen