In arid highland environments harsh conditions for vegetation establishment prevail. Plants in these environments develop different strategies to survive, including associations with fungal root endophytes. These associations may improve plant growth, helping plant resistance to adverse environments. The aim of this study was to determine the relationship among arbuscular mycorrhizal fungi (AMF), dark septate endophytes (DSE) and dominance degree of Poaceae in arid highlands of Argentine Puna. We studied AMF and DSE root colonization, and rhizospheric hyphal densities of dominant and subordinate grass species. Dual and positive associations between AMF and DSE prevailed. Dominant grasses had the highest levels of AMF and DSE root colonization. Dominant and intermediate grasses were associated with the highest values of rhizospheric hyphal density. In Puna highlands, the interactions among AMF, DSE and grasses suggest that fungal root endophytes may play a role in structuring grass communities by differentially improving the resistance to harsh conditions.