Abiogenic iron oxidation at the olivine surface is required for fungal weathering

While abiogenic Fe oxidation at the silicate surface controls abiotic dissolution kinetics, its influence on biotic dissolution remains unclear. To explore this relationship, we ran dissolution experiments with the rock-inhabiting fungus Knufia petricola and natural olivine (Fo91) or its Fe-free analogue, synthetic forsterite (Fo100), buffered at pH 4 or pH 6. Abiotically, olivine dissolved over hundred times slower than forsterite at pH 6. K. petricola enhanced the dissolution of olivine at pH 6, had no effect on forsterite dissolution, and even inhibited olivine dissolution at pH 4. Our results suggest that in buffered environments, fungi can only drive mineral dissolution by counteracting the inhibition caused by processes like abiogenic Fe-oxidation.