Abstract
Summary: Lolium perenne L. and Holcus lanatus L. were grown together in 125‐mm pots in a factorial experiment combining mycorrhizal infection and root competition. Both root competition and mycorrhizal infection gave a slight advantage to H. lanatus but, in combination, these produced considerable suppression of Lolium perenne. Root length of L. perenne was reduced by mycorrhizal infection, which was itself increased by competition. The competitive effects can be explained solely in terms of mycorrhizal infection.