In vitro weathering of phlogopite by ectomycorrhizal fungi .1. Effect of K+ and Mg2+ deficiency on phyllosilicate evolution

The ways in which ectomycorrhizal fungi benefit tree growth and nutrition have not been fully elucidated. Whilst it is most probably due to improved soil colonization, it is also likely that ectomycorrhizal fungi could be directly involved in nutrient cycling of soil reserves. This study assessed access by two species of ectomycorrhizal fungi to soil nonexchangeable K+ reserves. The incubation of ectomycorrhizal fungi in bi-compartment Petri dishes with phlogopite led to cation exchange reactions and to crystal lattice weathering. Paxillus involutus COU led to irreversible phlogopite transformations, while Pisolithus tinctorius 441 led to reversible ones. Simultaneous depletion in K+ and Mg2+ led to an enhanced weathering of phlogopite by P. tinctorius 441. The observation of phlogopite evolution shows that some specific Al3+ immobilization occurred under P. tinctorius 441. The data suggest that these bio-weathering mechanisms could be related to the release of fungal organic acids or other complex forming molecules.