Weathering of ammonium- or calcium-saturated 2:1 phyllosilicates by ectomycorrhizal fungi in vitro

The ways through which ectomycorrhizal fungi benefit tree growth and nutrition have not been totally elucidated. Our study was therefore aimed at assessing fungal access to soil exchangeable and stable mineral reserves. The growth of different ectomycorrhizal fungi in bi-compartment Petri dishes with NH4+- or Ca-saturated vermiculite led to cation exchange reactions and to crystal lattice weathering. The presence or absence of soluble NH4+ or Ca did not seem to affect fungal mobilization potential. Oxalic acid appears to be involved in vermiculite weathering by Paxillus involutus and Ca ions could limit the acid dissolution of Ca-saturated vermiculite. The quantitative significance of such cation mobilization and mineral weathering still has to be assessed in situ and in association with ectomycorrhizal plants.