Grazing Effects Oo Mycorrhizal Colonization and Floristic Composition of the Vegetation on a Semiarid Range in Northern Nevada

Abstract

The effect of grazing on the colonization of range plants by vesicular-arbuscular mycorrhizal (VAM) fungi was investigated within an exclosure and on degraded Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) rangelands at Medell Flat, near Reno, Nev. Implications of the interaction between mycorrhizae and grazing, relevant to the ecology and management of rangelands, are discussed. Density of forage grasses and their colonization by VAM fungi was significantly reduced as a result of grazing, in some cases by more than 50%. No differences in colonization were found in forage or nonforage broadleaf plants. A significant shift in the floristic composition and density of range plants occurred as a result of the presence or absence of grazing pressure. The decrease in VAM-fungal colonization of grasses under grazing is ascribed to a decrease in leaf areas and an increase in root to shoot ratios-conditions which result in decreased source capacity and increased sink demand.