WEATHERING OF AMMONIUM OR CALCIUM-SATURATED 2 1 PHYLLOSILICATES BY ECTOMYCORRHIZAL FUNGI IN-VITRO/

The ways through which ectomycorrhizal fungi benefit tree growth and n utrition have not been totally elucidated. Our study was therefore aim ed at assessing fungal access to soil exchangeable and stable mineral reserves. The growth of different ectomycorrhizal fungi in bi-compartm ent Petri dishes with NH4+ or Ca-saturated vermiculite led to cation e xchange reactions and to crystal lattice weathering. The presence or a bsence of soluble NH4+ or Ca did not seem to affect fungal mobilizatio n potential. Oxalic acid appears to be involved in vermiculite weather ing by Paxillus involutus and Ca ions could limit the acid dissolution of Ca-saturated vermiculite. The quantitative significance of such ca tion mobilization and mineral weathering still has to be assessed in s itu and in association with ectomycorrhizal plants.