INFLUENCE OF N-2-FIXING TRIFOLIUM ON PLANT-SPECIES COMPOSITION AND BIOMASS PRODUCTION IN ALPINE TUNDRA

Alpine Trifolium species have high rates of symbiotic N-2-fixation whi ch may influence the abundance and growth of plant species growing nea r them. The potential for facilitative effects on plant abundance and growth in dry meadow alpine tundra of Niwot Ridge, Cole., characterize d by low resource availability, was investigated by measuring soil N, aboveground biomass production, and plant species composition in patch es of Trifolium dasyphyllum and surrounding tundra. Extractable inorga nic N was more than twofold greater and extractable P was 27% lower in Trifolium patches than in surrounding tundra. Aboveground production was twofold greater in Trifolium patches than in surrounding tundra. H owever, the difference was largely due to the production of T. dasyphy llum relative to the non-Trifolium? component of biomass, which was no t different between the Trifolium patches and surrounding tundra. In t he Trifolium patches, the proportion of graminoid biomass was lower wh ile the proportion of forb biomass was higher relative to surrounding tundra. Although the abundance of some species was positively associat ed with the presence of Trifolium, other species were less abundant, p ossibly due to increased competition for P and differential abilities of alpine species to respond to increased N availability. Trifolium ma y exert both facilitative and inhibitive effects on dry meadow alpine species and, in the process, substantially influence the spatial heter ogeneity in community structure and primary production.