Brazilian pine (Araucaria angustifolia, Araucariaceae) is one of the few native gymnosperms from southern Brazil. In Rio Grande do Sul, it occurs mainly in the highlands of the planalto region, as a tree-component of the mixed ombrophyllous forests. The species is valuable for its wood, edible seeds, and ornamental use, and is today listed as a threatened species. This tree-species establishes associations with arbuscular mycorrhizal fungi, and assessing the impact of such association to the species-performance will help us in defining the management procedures for its use in conservation and sustainable purposes. In this study, we tested the nutritional and growth responses of seedlings to inoculation with Glomus clarum, a fungal species identified in the rhizosphere of Brazilian pine in natural stands. A greenhouse study was conducted, where plants were either inoculated with G. clarum or with a sterilized version of the same inoculum. Plant growth was evaluated over a 21-month period by measuring the total shoot length, and, at the end, by plant dry mass, leaf nutrient content, and root colonization. Seedlings inoculated with G. clarum had a high degree of mycorrhizal colonization of their roots (81%). The inoculated seedlings grew significantly more (312% mass increase) than the controls, which had a higher root:shoot ratio than the inoculated seedlings. Leaf concentrations of P, K, Na, and Cu were higher while those of Ca, Mg, Fe, Mn, and B were lower in the inoculated plants. The results indicate a strong response of A. angustifolia to mycorrhizas, suggesting a high degree of dependence of the species on these associations.