Predicting silicate weathering rates over large space and time scales remains limited by current understanding of mineral reactivity. In particular, relating mineral-microorganism interactions to the temporal decrease of silicate weathering rates resulting from surface aging is still not fully understood. Here we examine the interplay between bacteria from natural soil solutions and tailored (fresh or aged) mineral powders aimed at simulating short- and long-term fluid-mineral interactions. Mineral-specific bacterial communities developed within 7 weeks on mineral surfaces and were not significantly affected by chemical modifications of the silicate surface resulting from laboratory aging (i.e., development of amorphous silica-rich surface layers, ASSLs). Dissolution rates of aged mineral powders remained one order of magnitude lower than those of fresh powders, despite a small increase of the dissolution rate (≤30%) for biotic experiments with olivine powders. This increase could be attributed to bacterial mobilization of iron during bacterial colonization of olivine surfaces devoid of ASSLs. Bacteria did not restore the reactivity of aged powders by active hydrolysis of the ASSLs, and thus may not counterbalance mineral surface aging in the critical zone over longer time scales.
Early stages of bacterial community adaptation to silicate aging