| Summary: | We used 15N soil-labeling techniques to examine how the dominant species in a N-limited, tussock tundra plant community partitioned soil N, and how such partitioning may contribute to community organization. The five most productive species were well differentiated with respect to the chemical form (ammonium, nitrate and glycine), season (June and August), and depth (3 and 8 cm) of N uptake. Species dominance (productivity) was positively correlated with the similarity between the uptake and availability of native forms of N, suggesting that competition and resource partitioning have strongly influenced the organization of this community. We are further investigating this hypothesis by examining the degree of spatial overlap among species that are similar or dissimilar in their use of N. Uptake of 15N injected at different distances from individual plants showed significant interspecific differences in lateral rooting areas and a high potential for overlap of rooting areas among species. We illustrate how the "total" overlap among species can be calculated from the lateral overlap of rooting areas and the degree of ecological overlap measured by 15N partitioning, and how this new measure of overlap can be used to test whether resource competition has contributed to the spatial organization of this community.
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