Molecular diversity of arbuscular mycorrhizal fungi associated with two co-occurring perennial plant species on a Tibetan altitudinal gradient.

Plant communities on Mount Segrila on the Tibetan Plateau show distinct changes at different altitudes, but little information is available on belowground communities of arbuscular mycorrhizal fungi (AMF). Root samples of two co-occurring species, Pennisetum centrasiaticum and Kobresia sp., growing in open grasslands at eight altitudes (3,446-4,556 m) were analyzed for diversity of AMF by PCR, cloning, and sequencing. Dominant plants were well colonized by AMF even at higher altitudes where spore density in rhizospheres decreased dramatically. A total of 29 operational taxonomic units (OTUs) of AMF were detected, and some novel sequence types were found. Acaulosporaceae and Glomeraceae were the dominant families. There was no significant difference in OTU richness along elevational gradients in Kobresia sp., but OTU richness in P. centrasiaticum was higher at intermediate elevations. Elevation, host plant species, and soil variables (pH, soil organic matter, and available P and N) were found to have significant effects on the overall AMF community across all elevations. Fungal community composition differed significantly between the two plant species at each elevation, and the similarity was generally higher at the intermediate elevations. No significant difference in compositional similarity was observed for Kobresia sp. with increasing elevation, but the dissimilarity increased significantly for P. centrasiaticum. These results suggest that host identity is an important determinant for the structure of the AMF communities along the elevational gradients in high altitude environments.