SPATIOTEMPORAL DIFFERENCES IN N-15 UPTAKE AND THE ORGANIZATION OF AN OLD-FIELD PLANT COMMUNITY

Investigated the hypothesis that spatial and temporal differences in nitrogen uptake facilitate species' coexistence in a nitrogen-limited, old-field plant community at Cedar Creek Natural History Area, Minnesota. Differences among the 6 most abundant species were assessed by measuring aboveground uptake of 15N injected at 2 soil depths at 3 times during the growing season. Species were spatially and, to a greater extent, temporally differentiated into three groups. Differences in species' abundance between and within these groups suggest that spatiotemporal partitioning of N is a major determinant of community organization. Dominant species (Schizachyrium scoparium, Poa pratensis) were well differentiated and the abundances of subordinate species (Artemisia ludoviciana, Solidago nemoralis, Ambrosia coronopifolia, Panicum oligosanthes) were positively related to the degree of differentiation from dominant species. Subordinate species occupy "peripheral' spatiotemporal niches relative to Schizachyrium and Poa. This may promote coexistence by reducing diffuse competition. Results suggest that spatiotemporal resource partitioning slows the rate of competitive displacement among co-occurring plant species. -from Authors