Synergistic effect of a phosphate-solubilizing fungus and an arbuscular mycorrhizal fungus on leucaena seedlings in an Oxisol fertilized with rock phosphate

A greenhouse experiment was conducted to determine the effects of a phosphate-solubilizing fungus (Mortierella sp.) and an arbuscular mycorrhizal fungus (Glomus fistulosum (Skou and Jakobsen)) in enhancing plant Pi uptake and growth of Leucaena leucocephala (Lam.) grown in an Oxisol fertilized with graded amounts of rock phosphate (RP). For this purpose, a surface soil sample was fertilized with four levels of the Huila RP (P = 0, 150, 300, and 600 mg.kg(-1)) and inoculated with none, one, or both fungi. In the unfertilized soil, leucaena plants grew poorly and there was no plant response to individual or dual inoculation. When RP was added G. fistulosum significantly increased plant Pi uptake and growth, the effect of inoculation was significantly higher at the P levels of 300-600 mg.kg(-1). Mortierella sp. was highly effective in increasing plant P uptake and growth of mycorrhizal leucaena, but it was ineffective in nonmycorrhizal leucaena across the RP gradient. The synergistic effects of dual inoculation were more evident on plant Pi uptake than on growth. The results indicate that the phosphate-solubilizing fungus effect was limited by soil Pi sorption. This limitation likely was overcome by the mycorrhizal association, which allowed a more efficient capture of the Pi released due to RP dissolution.