Arbuscular mycorrhizas are symbiotic associations that play a key role in plant nutrition by absorbing and translocating mineral nutrients from soil to host plants. Arbuscular mycorrhizal fungi, which are considered natural biofertilizers, show diverse levels of performance, depending on the ability of different isolates to promote plant growth and health. Here we investigated the performance of geographically different isolates of two fungal species, Glomus mosseae and G. intraradices, by assessing plant growth responses and P and N uptake in Medicago sativa, in order to select the most efficient fungi for this host plant. The four selected Glomus isolates significantly increased shoot dry weights and shoot N and P content of mycorrhizal plants, but their performances were different. In particular, G. intraradices IMA6 significantly differed from G. mosseae IMA1 in inducing larger growth responses relative to all parameters measured.