Assessing diversity of arbuscular mycorrhizal fungi in a local community: role of sampling effort and spatial heterogeneity.

Diversity of arbuscular mycorrhizal fungi (AMF) was assessed in two 9.2 x 9.2-m plots planted with landscape trees and shrubs at an experimental site in Phoenix, AZ, USA. Twenty-five soil samples were collected in a regular grid pattern from each plot, and AMF species were identified using trap cultures. A total of 12 species were detected, with 7 species detected in one plot and 11 in the other. We found that sampling effort had a major impact on assessing species richness and composition in this local community. Fifteen samples would be necessary to detect 70-80% of species present in each plot. A limited number of additional undetected species are likely to be present in both plots, based on the sampling effort curves and jackknife estimates. Only two species, Glomus eburneum and Glomus microaggregatum, were detected in over 50% of the samples from both plots, and rank-frequency plots revealed a lognormal species distribution. Despite the patchiness of plants in the plots, the number of species detected per point exhibited spatial structuring only at the smallest sampling scale in a single plot, and only a single species in each plot was not randomly distributed. These results indicate that sampling effort and strategy can affect perceptions of AMF community structure.