Plant species collected from tundra ecosystems located along a north-south transect from central Alaska to the north coast of Alaska showed large and consistent differences in (15)N natural abundances. Foliar ?(15)N values varied by about 10% among species within each of two moist tussock tundra sites. Differences in (15)N contents among species or plant groups were consistent across moist tussock tundra at several other sites and across five other tundra types at a single site. Ericaceous species had the lowest ?(15)N values, ranging between about -8 to -6‰. Foliar (15)N contents increased progressively in birch, willows and sedges to maximum ?(15)N values of about +2‰ in sedges. Soil (15)N contents in tundra ecosystems at our two most intensively studied sites increased with depth and ?(15)N values were usually higher for soils than for plants. Isotopic fractionations during soil N transformations and possibly during plant N uptake could lead to observed differences in (15)N contents among plant species and between plants and soils. Patterns of variation in (15)N content among species indicate that tundra plants acquire nitrogen in extremely nutrient-poor environments by competitive partitioning of the overall N pool. Differences in plant N sources, rooting depth, mycorrhizal associations, forms of N taken up, and other factors controlling plant N uptake are possible causes of variations in ?(15)N values of tundra plant species.