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Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, ¹⁵N natural abundance (δ¹⁵N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N₂ fixation associated with vascular plants was estimated with foliar δ¹⁵N and the basal area of leguminous plants. Soil and plant N was more ¹⁵N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N …