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Arbuscular mycorrhizal (AM) fungal infection was assessed for dominant Chihuahuan Desert annual and perennial plant species. Annuals were determined to have significantly less AM infection than their perennial counterparts. Additionally, annuals were shown to have significantly smaller fine root diameters than perennials. Within 15 of the 17 species examined, the presence of AM hyphae in a root segment was not a significant determinant of root diameter, indicating than in most plant species mycorrhizal infection is not directly promoting root diameter increases. The results of this survey show that the dominant plant species of the Chihuahuan Desert group into two categories: (i) short-lived annuals with thin roots and low AM dependency, (ii) longer-lived perennials with thick mycorrhizal roots. (C) 2003 Published by Elsevier Science Ltd.