Plant growth and reproduction can be reduced by severe livestock grazing pressure. In contrast, rangeland shrubs and mycorrhiza fungi may both provide soil moisture and nutrients for their coexisting plants. We tested the simultaneous effects of grazing and shrub canopies on the coexistent relationship between mycorrhiza and Bromus kopetdaghensis, in Baharkish rangelands, Quchan, Iran, during summer 2013. Plant and 40 soil samples were collected from understory of two shrubs (Astragalus mesedensis and Acantholimon erinaceum) and the adjacent open areas; in a grazing and/or an enclosure site. Furthermore, effects of shoot clipping were tested on the colonization rate under the glasshouse conditions. Root painting method was conducted based on Philips & Heyman, colonization rate based on Glovannetti & Mosse, and spore counting via the sucrose gradient method. Results indicated that colonization rate and spore numbers were significantly reduced both under the livestock grazing in the field (35%) and 27 % in the hand clipping treatments. Shrub canopies did not have any significant effect on the spore number and colonization rates under the high grazing pressure, whereas under the enclosure site, their colonization rate was reduced to 24% and their spores increased by 25%. In conclusions, high livestock grazing pressure has definite negative effects on the symbiosis, whereas the effects of shrub canopies are more complicated and varies depending on the grazing intensity and shrub species. This study found higher colonization rate with mycorrhiza for Astragalus spp compared to Acantholimon erinaceum.
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