Vesicular-arbuscular mycorrhizal infection of Quercus rubra seedlings.

•  The influence of vesicular-arbuscular mycorrhizal (VAM) host plants is reported on VAM infection of Quercus rubra seedlings, a predominately ectomycorrhizal species. •  In a field experiment, Q. rubra seedlings were planted near Quercus montana and Acer rubrum (a VAM host) stump sprouts and near dead Quercus spp. stumps. In a subsequent glasshouse study, seedlings of Q. rubra were grown with or without VAM inoculum (±V) and with or without Sorghum bicolor (±S), a VAM host. •  In the field experiment, seedlings planted near A. rubrum had greater VAM infection than other seedlings; ectomycorrhizal infection was greatest on seedlings near Q. montana. In the glasshouse experiment, VAM infection was increased in both extent (proportion of root length infected in roots of infected seedlings) and frequency (number of seedlings with infection) in the presence of S. bicolor. Seedling mass and N concentration were reduced in the +V treatment; however, these variables were not correlated with extent of VAM infection. •  VAM infection of Q. rubra is greatly enhanced in the presence of VAM hosts in both field and glasshouse conditions. No evidence for positive effects of VAM infection on Q. rubra seedlings was found.