Release of oxalate and protons by ectomycorrhizal fungi in response to P-deficiency and calcium carbonate in nutrient solution

The release of oxalate and H + by six ectomycorrhizal isolates (Hebeloma cylindrosporum 1 and 9, Paxillus involutus, Suillus collinitus 2 and 22, Rhizopogon roseolus), able to grow in vitro with NO 3 -as the sole source of N, was measured in response to orthophosphate (Pi) concentration (20, 100 and 500 M Pi) and CaCO 3 (+500 M Pi) in the solution. Without CaCO 3 , all isolates excepted H. cylindrosporum ones released oxalate. For each isolate, oxalate production was not related to P-deficiency but was strongly enhanced by CaCO 3 . Whatever the medium composition, H. cylindrosporum alkalinised the solution. Among oxalate-producing fungi, S. collinitus 22 and R. roseolus exhibited an important proton efflux that could be related to transport phenomena for oxalate excretion. CaCO 3 enhanced both oxalate and proton efflux, increasing the chemical action exerted by the fungi on the mineral. oxalate production / pH / ectomycorrhizal fungi / growth / mineral nutrition Rsum -Libration d'oxalate et de protons par les champignons mycorhiziens en rponse une carence en P et en carbonate de calcium dans la solution nutritive. La libration d'oxalate et de protons par six isolats fongiques ectomycorhiziens (Hebeloma cylindrosporum 1 et 9, Paxillus involutus, Suillus collinitus 2 et 22, Rhizopogon roseolus), capables de se dvelopper sur NO 3