Categories of vesicular-arbuscular mycorrhizal dependency of host species

Summary

Brassica nigra and selected species of Leucaena and Sesbania were used as indicator hosts in a greenhouse experiment designed to establish distinct categories of mycorrhizal dependence. The plants were grown in an oxisol with different concentrations of established soil solution P in the presence or absence of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum. The extent to which the plant species depended on the fungus for dry matter production diminished with increased concentrations of soil solution P, but the magnitude of this decrease varied from species to species. Five distinct mycorrhizal categories are proposed based on the differences observed, ranging from non-dependent to very highly dependent. The critical soil solution P concentrations that were useful for separating host species into distinct VAM-dependency groups were 0.02 and 0.2 mg/l. Species differing in their mycorrhizal dependency differed with respect to the soil solution P concentration required for the expression of maximum VAM effectiveness, the degree to which increasing concentrations of P depressed VAM infection and the pattern of immobile nutrient accumulation.