Arbuscular mycorrhizal fungi exchange soil nutrients for carbon from plant hosts. Empirical works suggests that hosts may selectively provide resources to different fungal species, ultimately affecting fungal competition. However, fungal competition may also be mediated by colonization strategies of the fungi themselves. To test whether host quality drives fungal colonization strategies, we allowed competing fungi access to the roots of plants that varied in quality (manipulated by shading). We used quantitative PCR and microscopy to assess fungal competitive dynamics and found that shaded plants were not left as an open niche for less competitive fungi. However, while competitive fungi outcompeted less competitive fungi, the intensity of this effect depended on the quality of the host, with the strongest differences found on low-quality (shaded) hosts. Our results suggest that environmental conditions for the host aboveground play a role in the competitive interactions among fungi belowground.