Faeth 97 27020 Endophytic fungi frequently live intracellularly within the tissues of plants with little obvious indication of their presence. In grasses these symbionts have been thought to increase plant resistance to herbivory, resistance to drought, and the competitive abilities of some plants in their interactions with their neighbors. Despite the widespread occurrence of these associations, however, information on the nature of fungal-plant interactions remains limited. This project will continue investigations of the relationship between endophytic fungus, Neotyphodium, and Arizona fescue an economically important range grass in the southwest. An earlier series of experiments, funded by the Ecology program at NSF, failed to demonstrate that these fungi, provide any resistance to grazing by invertebrate herbivores, in contrast with widely held conventional wisdom that such a resistance is provided. Alternative hypotheses to be tested in this new work center on the observation that plants increase root biomass and, possibly, osmoregulatory efficiency when infected by fungi. It will examine the varying survival of seed, seedling, and mature-plant stages of fescue under different conditions of soil moisture and nitrogen along with fire frequency and intensity for different plant genotypes. It will employ a series of field and laboratory experiments to test the notion that the Neotyphodium-Arizona fescue mutualism is context dependent. It will also consider that fire may be an evolutionary factor that maintains these associations. The results of this work will increase the understanding of the role of microoganisms in plant-animal interactions, plant population dynamics and the organization of plant-microbe-herbivore communities. It will shed insight into the evolution, ecology and maintenance of mutualistic interactions. It will also provide useful information for the maintenance important southwestern grasslands.
