Can distribution of trees explain variation in nitrous oxide fluxes?

The impact of distance to tree stems on nitrous oxide (N(2)O) fluxes was examined to determine whether it is possible to improve the accuracy of flux estimates from boreal forest soils. Dark static chambers were placed along transects between pairs of trees within a Norway spruce stand and fluxes of N(2)O and carbon dioxide (CO(2)) were measured during the period 1999 - 2003. The groundwater table was measured on every sampling occasion along the transects. In addition, radiation transmission, potential diffusion rate and biomass of forest floor vegetation were measured once at each chamber site along one of the transects and soil samples were collected at three depths, from which pH, denitrification enzyme activity, soil moisture, organic matter, and carbon and nitrogen content were determined. There was a high level of variation in the N(2)O fluxes, both spatially and temporally. However, the spatial variation in the N(2)O fluxes within the transect could not be explained by differences in any of the measured variables. Sometimes, mainly when no major peaks occurred, N(2)O fluxes were significantly correlated with CO(2) release. It is concluded that distance to stems cannot be used to improve the design of sampling schemes or for extrapolating flux levels to larger scales.