Patterns of species composition and distribution of arbuscular mycorrhizal fungi 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 North America were compared with each other and with AM fungal communities in the Namib Desert in Africa using successive trap cultures to induce sporulation. Twenty-one AM fungal species were recovered, eight of which were undescribed. Species richness at each sampling site ranged from 6 to 12 species. There was considerable overlap in the species composition of the two desert regions surveyed in North America. Glomus microaggregatum Koske, Gemma and Olexia, Glomus etunicatum Becker and Gerd., Glomus intraradices Schenck and Smith, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, Glomus spurcum Pfeiffer, Walker and Bloss, and two undescribed Glomus species (AZ112 and AZ123) were detected in over 50% of the sampling sites in North America. Similarities 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 limited mostly to small-spored fungi in Glomaceae and Acaulosporaceae. Acaulospora trappei Ames and Linderman, Glomus etunicatum, Glomus intraradices, Glomus 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 and Schenck was 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 selective variables at the local level in determining species composition in arid environments.