This study assessed the effects of stress (grazing) on VAM-fungal colonization of a major forage species, crested wheatgrass (Agropyron desertorum). Changes in root colonization of crested wheatgrass plants by VAM fungi were measured under three levels of grazing pressure, ranging from no grazing to heavy, continuous grazing. VAM-fungal spore samples were statistically analyzed for root/shoot ratios, fungal colonization of roots, fungal biomass, and P contents of roots and shoots in each grazing regime. Heavy grazing reduced VAM-fungal colonization biomass and percentage of colonization per amount of root length, VAM spores per 100 g soil and the root/shoot ratio of crested wheatgrass over samples from the ungrazed plots. Severe grazing adversely affects the colonization of crested wheatgrass by VAM fungi. This reduction in the fungal symbiont may have an effect on plant nutrition and soil structure and stability.
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