In two pot experiments with a soil deficient in P and N, vesicular-arbuscular mycorrhizas stimulated the shoot growth of Lolium perenne L. greatest (24%) with the highest levels of applied P and/or N, and where the shoot N and P concentrations approached the normal agronomic range. It is suggested that applied N, and possibly P, resulted in mycorrhizas making a more important contribution to the plant's P or Cu status. Previous experiments purporting to show the mycorrhizal dependency of species are criticized if the levels of nutrients in the soil (other than P) which might have been limiting were not considered.
Mycorrhizas reduced root/shoot ratios even in those treatments where a growth response was not detected.
There was a negative relationship within treatments between responsiveness to mycorrhizas and the size of the non-mycorrhizal plant. This may have relevance in plant breeding.