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.

NO and N2O emissions from agricultural fields in the North China Plain: Origination and mitigation

“…A small contribution occurred after topdressing for the maize and basal fertilization for the wheat, but evident contribution was evoked after basal fertilization for the maize and topdressing for the wheat. Additionally, other studies also found the important contribution of denitrification on N 2 O emission from agriculture soil (Vilain et al, 2014), grassland (Ostrom et al, 2010;Vilain et al, 2014) and forest soil (Cheng et al, 2014;Morse et al, 2014;Vilain et al, 2014). In this study, because each fertilization event is accompanied with immediately irrigation, it is difficult to explain the above phenomena only based on the variation of soil anoxic condition caused by the soil moisture (Figs.…”

Preindustrial nitrous oxide emissions from the land biosphere estimated by using a global biogeochemistry model

“…In contrast, as the largest terrestrial biome, boreal forests lack available N because the rate of BNF is restricted by cold temperatures and low precipitation during the growing season (Alexander and Billington, 1986). Morse et al (2015) conducted field experiments in northeastern North American forests. They found that denitrification does vary coherently with patterns of N availability in forests, and there are no significant correlations between atmospheric N deposition, potential net N mineralization, and nitrification rates.…”

Inference of Soil Hydrologic Parameters from Electronic Soil Moisture Records

“…For example, it is understood that saturation may never be achieved in well drained soils under field conditions (Wang et al, 1998). Field saturation, fs , accounts for gas filled soil pore space that may be occluded within the pore matrix at approximately the bubbling pressure (Reynolds et al, 2002) and can occur due to air encapsulation (Fayer and Hillel, 1986), fluctuating groundwater levels (Marinas et al, 2013), and biogenic gases (Morse et al, 2015).…”