Effect of a phosphate-solubilizing fungus and an arbuscular mycorrhizal fungus on leucaena seedlings in tropical soils with contrasting phosphate sorption capacity

A greenhouse experiment was conducted to determine the effects of a rock phosphate-solubilizing fungus (Mortierella sp.) and an arbuscular mycorrhizal fungus (Claroideoglomus claroideum (N. C. Schenck & G. S. Sm.) C. Walker & A. Schuler comb. nov.) on enhancing plant phosphate (P) uptake and growth of Leucaena leucocephala (Lam.) in three tropical soils that exhibited contrasting soil P sorption capacities. For this purpose, the three soils (Mollisol, Oxisol and Andisol) were amended with Huila rock phosphate (RP) at a P rate of 300 mg kg(-1) and inoculated with neither, one, or both fungi. The results indicate that a three-way interaction occurred for all variables studied and that the effectiveness of the PSM in increasing plant P uptake and growth was limited by the soil P sorption. For instance, PSM inoculation was ineffective in the Andisol (very high P sorption capacity) even when the mycorrhizal association was present, while in the Oxisol (medium P sorption) the PSM was only effective when the plant was concomitantly inoculated with the AMF (dual inoculation). In contrast, both individual PSM inoculation and individual AMF inoculation were effective in promoting plant P uptake and growth in the Mollisol (low soil P sorption); however, the effect was even higher in the presence of both (dual inoculation). Although the PSM effect was limited by soil P sorption, this limitation likely was overcome by the mycorrhizal association, which permitted a more efficient capture of the P released from RP dissolution.