Diversity of arbuscular mycorrhizal fungal species in soils of cultivated soybean fields
Mycorrhizae are presumably important contributors to plant growth in most ecosystems. Our objective in this study was to evaluate the population diversity of arbuscular mycorrhizal (AM) fungi in Clarion (well drained) and Webster (poorly drained) soils of four Iowa soybean [Glycine max (L.) Merr.] fields. These soils normally occur together on the landscape, with Clarion in the upland and Webster in lowland positions. Previous work consistently has shown higher AM fungal spore counts in Webster soils. Spore morphology was used for the characterization of fungal species. Identification of certain species was confirmed using polymerase chain reaction (PCR)-based rDNA fingerprinting. Glomus claroideum, G. etunicatum, G. mosseae, G. viscosum, and Paraglomus occultum-like spores were prevalent in both Clarion and Webster soils. Trap cultures led to detection of several additional AM fungal species, including G. clarum, G. coronatum, G. fasciculatum, G. vesiforme, Acaulospora calossica, and Entrophospora infrequens. The richness of the Glomus species varied from eight species in Webster soil of a field with highest available P (203 mg kg–1 soil Bray P1), where spores of G. mosseae constituted 90% of the spore population, to 12 species in Clarion soil, with lowest available P (14 mg kg–1 soil Bray P1). The variability of AM fungal density and distribution was also high among samples taken only 2 m apart. Although diverse within the genus, this study showed the dominance of Glomus species in field soils used to produce two important commercial crops, corn (Zea mays L.) and soybean, in the midwestern United States.