ANNUAL NITROUS-OXIDE FLUX AND SOIL-NITROGEN CHARACTERISTICS IN SAGEBRUSH STEPPE ECOSYSTEMS

Soil nitrogen transformations and nitrous oxide fluxes were measured in a range of sagebrush steppe ecosystems in south-central Wyoming. Net nitrate production, measured in laboratory incubations, was highest in the ecosystem type dominated by Artemisia tridentata ssp. vaseyana, especially early in the growing season. Fluxes of nitrous oxide, measured in closed chambers and analyzed by gas chromatography, also tended to be higher in the same type, but only for short periods in the spring. Thereafter, all nitrous oxide fluxes were low and did not differ consistently among types. Estimated average annual fluxes for three Artemisia ecosystem types (dominated by Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, and Artemisia nova) were 0.32, 0.23 and 0.13 kg N2O-N ha-1y-1 respectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N2O-N ha-1y-1. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 x 10(9) g y-1 of N2O-N from U.S. sagebrush steppe, and a flux of 1.1 x 10(11) g y-1 of N2O-N from analogous desert and semi-desert shrublands of the world.