Abstract
Assessment of the microbial impact on mineral dissolution is crucial for a predictive understanding of basic (Ca, Mg bearing) silicate weathering and the associated CO2 consumption, bioerosion, and CO2 storage in basaltic rocks. However, there are controversies about the mechanism of microbial effect, which ranges from inhibiting via nil to accelerating. Here we studied diopside interaction with the heterotrophic bacterium Pseudomonas reactants and the soil fungus Chaetomium brasiliense using a combination of mixed-flow and batch reactors and in situ (AFM) and ex situ (SEM) microscopy. The results provide new nano-level insights into the degree to which microorganisms modify silicate dissolution. Taking into account negligible effects of organic ligands on diopside dissolution as reported earlier, we conclude that the microbial effect on Ca-Mg silicates is weak and the acceleration of dissolution of “basic” silicate rocks in the presence of soil biota is solely due to pH decrease in porewaters.
Highlights
Chemical weathering of basic (Ca and Mg bearing) silicates is a primary factor regulating the climate of our planet via a long-term CO2 uptake from the atmosphere[1]
In bacteria-free experiments, diopside dissolution rates decreased by ca. 0.5–1 order of magnitude during the pH decrease from 6 to 9 (Fig. 1, Table 1)
The dissolved organic carbon (DOC) concentration remained fairly stable in the course of given bacterial experiment and generally ranged from 7 to 25 mg L−1 being the highest at highest biomass concentration
Summary
Chemical weathering of basic (Ca and Mg bearing) silicates is a primary factor regulating the climate of our planet via a long-term (million year scale) CO2 uptake from the atmosphere[1]. Several experimental works performed over the past two decades unambiguously demonstrated the lack of any sizable impact of CO2 and organic ligands (at otherwise constant pH) on Ca- and Mg-bearing mineral dissolution at typical soil water environments The reason for this is rather weak complexation of organic ligands with >CaOH2+ and >MgOH2+ surface sites responsible for the rate-controlling Mg–O and Ca–O bond breaking in these minerals[23,24,25,26,27,28,29,30]. We were able to separate the effect of pH from that of bacterial presence using a mixed-flow and batch reactor systems coupled with an in situ and ex situ microscopic examination of reacted surfaces
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