Soil nitrous oxide dynamics associated with forest harvesting in a transitional temperate-boreal forest ecosystem

The role of forest harvesting on nitrous oxide (N2O) production in and emission from soils is still poorly understood in northern environments. In this study N2O surface fluxes, coupled with subsurface soil air N2O concentrations, were measured at 2 forest and post-harvest pairs of contrasting soil texture in Nova Scotia, Canada between March and November, 2005. No significant difference in the magnitude of N2O surface fluxes between treatments was observed in this study. All sites acted as both sources and sinks of N2O over the sampling period. Surface fluxes observed at the forested sites ranged from -811ugN 2O-N/m2/day to 1367ugN2O-N/m 2/day with a median of 9ugN2O-N/m 2/day, while fluxes observed at the 4 year post-harvest sites ranged from -629ugN2O-N/m2/day to 583 ugN2O-N/m2/day, with a median of 9 ugN2O-N/m2/day. Fluxes from all sites were highly variable and showed no significant temporal patterns. On the other hand, subsurface soil air N2O concentrations were significantly higher at harvested than forested sites, with high variability observed at both sites. Subsurface soil air N2O concentrations at the forested sites ranged from 85ppb to 50667ppb, with a median concentration of 361ppb, and the harvested sites ranged from 80 to 27323ppb, with a median concentration of 413ppb. The magnitude of N2O surface fluxes and subsurface soil air N2O concentrations were examined to determine whether a positive relationship existed between the two variables. Relationships were observed more often during the drier, warmer months at these sites, however this relationship was not always predictable. This points to the presence of a sink of N 2O during transport through the soil profile in these soils. Both N 2O surface fluxes and subsurface soil air N2O concentrations were spatially and temporally transient, with some minor evidence of persisting microsites of both elevated N2O surface fluxes and subsurface soil air N2O concentrations over the sampling period.