9403308 Johnson This research will ascertain what factors regulate mycorrhizal effectivity in relation to mutualistic or parasitic relationships with their host plants. To be tested is the hypothesis that enrichment of a limiting soil resource causes mycorrhizal plants to allocate less carbon to root exudates, giving a selective advantage to parasitic forms of vesicular - arbuscular mycorrhizal (VAM) fungi. Fieldwork will be conducted on 24 fertilized, irrigated, and control plots at two NSF Long Term Ecological Research (LTER) sites (Minnesota's Cedar Creek Natural History Area and Sevilleta in New Mexico). %%% VAM fungi, relatively better studied in agricultural systems, are poorly known in natural ecological communities and ecosystems despite their ubiquitousness in soils. Nevertheless even in managed agricultural settings, these fungi are still largely regarded as "black boxes" in comparison to our knowledge of other components of agroecosystems. A more thorough understanding of VAM biology and ecology is likely to lead to improved practices by ranchers and farmers with regard to successful mycorrhizal inoculation programs, while a more comprehensive appreciation of natural mycorrhizal biodiversity will undoubtedly lead to as yet unforeseen improvements in managed agricultural and forest systems. ***
