Ectomycorrhizal fungi were grown in the liquid culture medium for 14 to 21 days.The efflux rates of H\++ and oxalate by the fungi were increased as the concentration of potassium decreased in the medium.Taking into account of potassium replacement in the interlayer of 2∶1 clay minerals by H\++ and the weathering of Al\|O lattices by oxalate,the higher ability of potassium mobilization by ectomycorrhizal fungi could occur in insufficient potassium systems than that in sufficient ones.Moreover,H\++ in the li...