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Many arbuscular mycorrhizal (AM) fungal species have worldwide distributions. However, it is not clear whether such species have adapted to local conditions. We compared the responses of mesic temperate and semi-arid tropical isolates of Glomus mosseae and Glomus etunicatum to extremes of temperature and moisture in a pot experiment. Treatments (warm–moist, warm–dry, freeze/thaw–moist, freeze/thaw–dry) were applied to whole soil mycorrhizal inoculum, and their effects were evaluated as both the change in viability of extraradical hyphae and mycorrhizal colonization of bait plants. Moist soil decreased hyphal viability compared with dry soil, irrespective of temperature, but mycorrhizal colonization of bait plants was lower in moist soil only when warm. Frost-heave could have physically ruptured hyphae in the freezing–moist soil without an effect on spores, but parasitism and (or) respiratory depletion of carbon reserves may have reduced survival of all propagules in the warm–moist soil. Hyphae of semi-arid tropical isolates survived all treatments better than hyphae of mesic temperate isolates, but these differences were not reflected in mycorrhizal colonization of bait plants. We found no evidence that these isolates have adapted to local conditions of moisture and temperature. Instead, wide environmental tolerances seem to be present within both populations of these AM fungal species. [ABSTRACT FROM AUTHOR]