Grazing Effects on 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 veskular-arbuscular mycorrhizal (VAM) fungi was investigated within an cxclosure and on degraded Wyoming big sagebrush (Artemisia tridentatu ssp. wyominge&s) rangelands at Medell Flat, near Reno, Nev. Implications of the interaction between mycorrhiue 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-funpl colonization of grasses under grazing is ascribed to a decrease in leaf areas and an increase in root to shoot ratios-conditions which result ln decreased source capacity and increased sink demand. The interactionsbetween vesicular-arbuscular mycorrhizal (VAM) fungi, their host plants, and the soil are complex (Masse 1973) and little known in semiarid rangelands (Trappe 1981). Plants benefit from their VAM-fungal endophyte when available P in the soil is limiting (Mosse 1973) and within a certain concentra-The authors are presently research plant physiologist and soil scientist, U.S.

Arbuscular mycorrhizal fungi in degraded typical steppe of inner Mongolia

“…Similar results were reported by Eom et al (2001) and Uhlmann et al (2006). It was supposed that different AMF species may have different sensitivities to photosynthate stress (Bethlenfalvay and Dakessian, 1984). However, the morphological method used in the present study, which is based on the AM fungus spores, has limitations in that spore production is highly dependent on physiological parameters of the AMF and on environmental conditions.…”

“…Conventional wisdom might lead us to expect less AM colonization of host plants in the grazed grassland because the loss of leaf area might result in a decreased source capacity that would be insufficient to satisfy both root and AM fungal sink demands (Harley and Smith, 1983;Bethlenfalvay and Dakessian, 1984;Gehring and Whitham, 1994;Dhillion and Gardsjord, 2004). However, in the present investigation, colonization of roots by AM fungi of the four indicator plant species was not significantly lower in the degraded grassland in which the degradation which was mainly due to over-grazing.…”

Mycorrhizas in Grasslands: Interactions of Ungulates, Fungi and Drought

“…The influence of defoliation on the ability of a plant to support vesicular-arbuscular mycorrhizal (VAM) fungi is variable (Daft & El-Giahmi, 1978;Wallace, 1981;Same, Robson & Abbott, 1983;Bethlenfalvay & Dakessian, 1984). When mycorrhizal colonization is depressed by grazing, the mechanism most frequently cited is reduction of photosynthate available for fungi (Daft & El-Giahmi, 1978;Wallace, 1981;Bethlenfalvay & Dakessian, 1984).…”

“…When mycorrhizal colonization is depressed by grazing, the mechanism most frequently cited is reduction of photosynthate available for fungi (Daft & El-Giahmi, 1978;Wallace, 1981;Bethlenfalvay & Dakessian, 1984). However, a depression of mycorrhizal colonization does not always occur (Bethlenfalvay, Evans & Lesperance, 1985).…”

Fiscal Year 2016 Revegetation Assessment

“…Tumble mustard, western tansymustard, and most other early successional species found in sagebrush steppe communities are nonmycorrhizal (Bethlenfalvay and Dakessian 1984;Fontenla et. al.…”