Abstract. 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 N,O-N ha-'y-r repsectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N,O-N ha-'y-l. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 X lo9 g y-' of N,O-N from U.S. sagebrush steppe, and a flux of 1.1 X 10" g y-l of N,O-N from analogous desert and semi-desert shrublands of the world.

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Abstract. Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average of 0.66 kg/ha of N 2 0-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen mineralization and nitrate production were estimated in soil and forest floor using in situ incubations; fertilized soil mineralized 277 kg ha -' y-' in contrast to 18 kg ha-' y-1 in control plots. Relative recovery of 'NH 4 -N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in the atmosphere.

Fluxes of nitrous oxide were determined in several sites in drought‐deciduous tropical forest, an extensive but little‐studied biome. N2O‐N fluxes from eight sites within intact Mexican forest averaged 0.91 ng cm−2 h−1 during the wet season; they were virtually absent in the dry season. Two subsistence maize fields yielded increased soil N2O‐N fluxes, while five pastures were more variable. Watering during the dry season caused a substantial but short‐lived pulse of N2O. Similar fluxes were observed in less‐intensive sampling of dry‐forest sites in Hawaii and Costa Rica. Overall, N2O fluxes from soils of dry tropical forests appear to be similar to those from moist tropical forests during the wet season and very low during the dry season.

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