Semiarid and arid ecosystems cover more than one third of the terrestrial surface. But few efforts have been made to characterize the diversity and organization of fungal communities in these ecosystems. We analyzed the fungal community associated with the roots of dominant grasses, biological soil crust and rhizosphere soils at a semiarid grassland in New Mexico. Internal Transcribed Spacer (ITS) rDNA sequences collected from 2004 to 2007 were amplified using fungal specific primers and approximately 2000 sequences were obtained.

Results/Conclusions

Species richness was high: 244 operational taxonomic units spanning 23 orders; 40% of the soil OTUs and 70% of the grama OTUs were novel (less than 97% similarity with respect to sequences in the NCBI database). Rarefaction curves and diversity estimators do not show saturation. Soil and root-associated fungal communities are dominated by dark septate fungi belonging to the Pleosporales with a substantial overlap among rhizosphere and biological soil crust (Jaccard abundance similarity index 0.75). At least 10 different orders including endophytic, coprophilous, mycorrhizal, saprophytic and plant pathogenic fungi were found colonizing the roots of dominant grasses. Although richness was high, the dominant fungi within roots, were a novel group of dark septate fungi (DSF) within the order Pleosporales. Other evidence suggests that these organisms increase drought resistance and contribute to nutrient acquisition.