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Abstract
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 15N natural abundances. Foliar δ15N 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
δ15N values, ranging between about -8 to -6‰. Foliar 15N contents increased progressively
in birch, willows and sedges to maximum δ15N values of about +2‰ in sedges. Soil 15N
contents in tundra ecosystems at our two most intensively studied sites increased
with depth and δ15N 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 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 δ15N values of tundra plant species.