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Many riparian ecosystems are affected by flow regulation due to damming. In the and and semi-arid riparian zones of the western United States, the effects of flow regulation on overstory Populus populations is well understood, but less is known about impacts to other aspects of riparian ecosystems including the herbaceous community and its associated arbuscular mycorrhizal fungi (AMF). In this study, floodplain soil texture and chemistry, herbaceous cover and richness, and AMF richness and colonization were compared between unregulated and regulated reaches of the Verde River, Arizona. When compared to the unregulated reach, the regulated reach had sandier soil and lower nutrient concentrations along with lower herbaceous cover and a higher proportion of annual species. Despite these differences, AMF colonization, richness and community composition were similar between reaches. Species of AMF can be sensitive to the identity of the host plant and to soil texture, moisture and nutrient levels; however, conditions between the unregulated and regulated reach of the Verde may not be sufficiently distinct to produce differences in the AMF community. AMF may also have a transient response to flooding and sampling immediately after a flood event may be necessary to detect differences in the AMF community between reaches. (c) 2006 Elsevier Ltd. All rights reserved.