The objective of the proposed research is to understand how differences among plant species in fine root structure and dynamics in response to nutrient patches affects their ability to acquire soil resources particularly nitrogen. The overall hypothesis is that differences in fine root morphology (length, width, production of root hairs) and production (birth, death, and elongation rate) will determine the rate at which species can encounter and exploit soil resources that vary in space and time (i.e. their foraging ability). Previous work suggests there are difference among annuals and perennials in response to soil nutrients. this has led to the hypothesis that the replacement of annuals by perennials in successional fields may be partially due to the increased patchiness in soil resources over time and difference in the abilities of annuals and perennials to find and exploit these patches. Of particular interest is the timing of responses to nutrient patches which will be determined by measuring the demographic response of species. Several specific hypothesis will be tested in greenhouse and field experiments. By varying the distributions of nitrogen, and using 15 N as a tracer, the relationship between fine root morphology and dynamics and resource acquisition will be measured. Fine root dynamics (branching, growth, birth and mortality) will be measured in situ with video technology. This technology allows the response of individual roots to nutrient patches to be followed and related to species differences in below-ground morphology, growth, and ability to acquire soil resources. The results of these studies will contribute to the development of a more mechanistic understanding of soil resource acquisition by plants and to a better understanding of how competition for resources affects species distributions in terrestrial plant communities.
