02168naa a2200301 a 450000100080000000500110000800800410001910000200006024500550008026000090013552014360014465000220158065000090160265000250161165000130163665000210164965000110167065000090168165300250169065300130171565300110172870000150173970000120175470000150176670000160178170000150179777300540181216211171999-11-19       1996    bl ---       0--  u    #d1 aNADELHOFFER, K.  a15N natural abundances and N use by tundra plants.  c1996  aPlant 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 15N natural abundances. Foliar  15N values varied by about 10% among species within each of two moist tussock tundra sites. Differences in 15N 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  15N values, ranging between about -8 to -6%. Foliar 15N contents increased progressively in birch, willows and sedges to maximum  15N values of about +2% in sedges. Soil 15N contents in tundra ecosystems at our two most intensively studied sites increased with depth and  15N 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 15N contents among plant species and between plants and soils. Patterns of variation in 15N content among species indicate that tundra plants acquire nitrogenin 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  15N values of tundra plant species.  anitrate reductase  asoil  aCiclo do Nitrogênio  aIsótopo  aNitrato Redutase  aPlanta  aSolo  aCycling and Nitrogen  aIsotopez  aPlants1 aSHAVER, G.1 aFRY, B.1 aGIBLIN, A.1 aJOHNSON, L.1 aMCKANE, R.  tOecologia, Netherlandsgv. 107, p. 386-394, 1996.