Multiple arbuscular mycorrhizal (AM) fungi can colonize the same plant root system and different fungal species or even different isolates of the same species of AM fungi can differentially affect their host. However, little attention has been focused on the process of AM fungal competition for the same root system. Utilizing a complete factorial design, this study focuses on how two co-occurring species of AM fungi (Glomus claroideum and Scutellospora fulgida) colonizing the root system of big bluestem (Andropogon gerardii) may affect the host as well as one another.

Results/Conclusions

Andropogon growth was significantly reduced by G. claroideum in isolation. S. fulgida did not significantly alter Andropogon growth in isolation, but significantly improved Andropogon growth in the presence of G. claroideum. Suppression of the negative effect of a second AM fungal species is a novel mechanism for growth promotion. This observation of plant response might suggest that S. fulgida competitively suppresses G. claroideum. Measures of fungal sporulation, however, indicate that G. claroideum was not negatively affected by S. fulgida. Rather, G. claroideum significantly reduced the sporulation of S. fulgida. These competitive effects could drive the effects of the AM fungi on plant growth in future growing seasons.