Inoculation of seedlings of green ash (Fraxinus pennsylvanica Marsh.) with vesicular-arbuscular (YA) mycorrhizal fungi, significantly increased seedling heights, root collar diameters, dry matter accumulations and phosphorus (P) nutrition relative to control seedlings. The ability of these YA mycorrhizal fungi, which were isolated from low-P forest soils (5–7 mg kg−1), to enhance seedling growth in a high-P (148 mg kg−1) nursery soil provides evidence for the occurrence of YA mycorrhizal fungi which may be effective under both high and low soil P conditions. There was a significant positive correlation between foliar P concentration and percentage infection. Despite significant differences in tissue P concentrations among seedlings receiving different inoculum treatments, the degree of growth enhancement was the same. Growth increases due to enhanced P nutrition in seedlings with higher concentrations of foliar P may have been offset by an increased drain on host photosynthate via production and maintenance of greater amounts of fungal bomass, or may have been limited by the low K fertility of the nursery soil.
Colonization percentages in roots of seedlings of green ash were high despite high soil P concentrations. The pattern of infection development was unique for each YA mycorrhizal fungal species. A modification of the grid-line intercept technique was used to assess intensity of infection. Infection for all endophytes during the period of most rapid vegetative host growth was predominantly arbuscular. However, arbuscular intensity fluctuated during this period. Vesicles increased in number with time but always made up a small percentage of total infection.