Patterns of species composition and distribution of arbuscular mycorrhizalfungi in arid regions of southwestern North America and Namibia, Africa

Arbuscular mycorrhizal (AM) fungal communities at 13 sampling sites in two arid regions (Chihuahuan and Sonoran Deserts) and semi-arid grasslands in N orth America were compared with each other and with AM fungal communities i n the Namib Desert in Africa using successive trap cultures to induce sporu lation. Twenty-one AM fungal species were recovered, eight of which were un described. Species richness at each sampling site ranged from 6 to 12 speci es. There was considerable overlap in the species composition of the two de sert regions surveyed in North America. Glomus microaggregatum Koske, Gemma & Olexia, Glomus etunicatum Becker & Gerd., Glomus intraradices Schenck & Smith, Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, Glomus spurcum Pfeif fer, Walker & Bloss, and two undescribed Glomus species (AZ112 and AZ123) w ere detected in over 50% of the sampling sites in North America. Similariti es in species composition of arid regions of Namibia and North America also was high, ranging from 54 to 79%. The taxonomic range of AM fungi was limi ted mostly to small-spored fungi in Glomaceae and Acaulosporaceae. Acaulosp ora trappei Ames & Linderman, Glomus etunicatum, Glomus intraradices, Glomu s occultum Walker, Glomus microaggregatum, Glomus mosseae, Glomus spurcum, and an undescribed Glomus species (AZ123) were detected in all three desert regions and in semi-arid grasslands. Gigaspora rosea Nicolson & Schenck wa s the only species in Gigasporaceae detected, and then only at one sampling site in North America. Scutellospora species were not found. These results indicate involvement of both historical processes such as dispersal and se lective variables at the local level in determining species composition in arid environments.