EXTERNAL AND INTERNAL-P REQUIREMENTS OF PLANT-SPECIES DIFFERING IN THEIR MYCORRHIZAL DEPENDENCY

Species of plants distinctly differing in their dependence on vesicular-arbuscular mycorrhizal (VAM) symbiosis were grown in potted soil at soil solution P levels ranging from 0.003 to 0.6 mg L-1. Vesicular-arbuscular mycorrhizal colonization levels generally decreased with increase in soil solution P concentrations, the degree of decrease being more pronounced with decrease in VAM dependency of host species. Mycorrhizal inoculation effect (MIE) disappeared at a much lower soil solution P concentration in the marginally to moderately VAM dependent Sesbania species compared to MIE noted in Leucaena leucocephala, a very highly VAM-dependent species. Under nonmycorrhizal condition, the former species exhibited lower external and higher internal P requirement for dry matter production compared to the latter species.