The effect of aluminium on phosphate uptake by three isolated ectomycorrhizal fungi

Three ectomycorrhizal fungi, Laccaria bicolor, Lactarius hepaticus and Lactarius rufus, were grown in liquid medium for 2 weeks and used in short-term phosphate (P) uptake studies. At phosphate concentrations ranging from 1 to 100 μM the fungi exhibited a single affinity phase. The kinetic parameters for P uptake differed between species with K_m varying from 1.5 to 13.1 μM. V_max also depended on the buffer that was applied. P uptake by the fungi was severely reduced by aluminium (Al). This could be ascribed mainly to the complexing of phosphate by Al³⁺. Correcting for this decrease in phosphate concentration, the uptake by both Lactarius hepaticus and Laccaria bicolor was only slightly inhibited by Al, while P uptake by Lactarius rufus was even stimulated. The latter may be attributed to a reduction in surface potential caused by the trivalent Al cation, which in turn increases the concentration of the negatively charged phosphate ion in the near-membrane region.