Mobilization of P and CD from rock phosphates by rhizospheric microorganisms (phosphate-dissolving bacteria and ectomycorrhizal fungi)

Some rock phosphates used as fertilizers or to produce fertilizers contain cadmium and have been suspected to increase trace element content in soils. The bioavailability (immobilization, solubilization) of Cd and P from three rock phosphates (from West Africa and East USA) has been investigated, with phosphate-dissolving microorganisms (two ectomycorrhizal fungi P. tinctorius and S. granulatus and a bacterium Agrobacterium sp.) in pure culture and in pine (Pinus sylvestris L.) rhizosphere. In pure culture the fungi accumulated more Cd than the bacterium. In pine rhizosphere, the uptake of P and Cd by the plant increased with bacterial inoculation. The bioavailability of Cd from the different rock phosphates was less related to their Cd content than to their cristallinitY and solubility, and was relatively higher than P one.