Effect of vesicular-arbuscular mycorrhizal and phosphatase-producing fungal inoculation on growth and nutrition of white clover supplied with organic phosphorus

In a pot experiment white clover was grown for 50 d in two sterilized low phosphorus soils supplied with organic phosphorus as sodium phytate. Seed inoculation with Aspergillus fumigatus, a phosphatase-producing fungus (PPF), and soil inoculation with Glomus mosseoe, a vesicular-arbuscular mycorrhizal (VAM) fungus resulted in increased shoot and root dry mass and root length, phosphatase activity in soil and shoot concentrations of P and to a lesser extent of Mg. The effects on these parameters were most distinct upon combined inoculation treatment (PPF + VAM). A significant increase in hyphal length density and decrease in Mn concentration was observed only upon PPF + VAM treatment. Shoot concentrations of Cu and Zn were highly enhanced by VAM but not by PPF. Of the total P uptake the PPF contribution accounted for 39-41 %, VAM contributed 41-50 % and their combination resulted in 55-58 %, in comparison to only 38-40 % contribution due to soil microorganisms under unsterilized conditions. The depletion of organic phosphorus in the rhizosphere soil increased in the order (PPF + VAM) > VAM > PPF > unsterilized soil > sterilized soil. The results demonstrate the efficient use of phytate phosphorus by A. fumigatus and G. mosseoe and suggest that dual inoculation is superior to a single one.