Soil denitrification fluxes from three northeastern North American forests across a range of nitrogen deposition.

Morse, Jennifer; Durán, Jorge; Beall, Fred; Enanga, Eric; Creed, Irena; Fernandez, Ivan; Groffman, Peter

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 O status, or forest type. We quantified N and NO fluxes in the laboratory with an intact-core method and monitored soil O, 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 year 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.

NORTH America; DENITRIFICATION; FORESTS & forestry; ATMOSPHERIC nitrogen; WATERSHEDS; FOREST soils; SOIL microbiology

Oecologia, 2015, Vol 177, Issue 1, p17

0029-8549

Academic Journal

10.1007/s00442-014-3117-1