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Basalt is a widely available natural silicate rock that is suitable to use in agricultural setup due to its diverse plant-relevant nutrient content. Yet, it has a rather slow weathering rate compared to minerals such as olivine and wollastonite. This is hypothesised to be partially due to formation of Fe and Al precipitates that form around the minerals, blocking bicarbonate - active site interaction in time. Therefore an agent such as a bacterium that can solubilize Fe and Al precipitates may effectively increase basalt weathering rates.
This study investigates the potential of the plant-growth promoting rhizobacterium Bacillus subtilis that was observed to have potent effect on Fe solubility to enhance basalt weathering rate in soil, thus increasing carbon sequestration. B. subtilis was reported to enhance weathering under laboratory conditions, but there is lack of data for natural conditions. We tested three cases in a soil-mesocosm experiment at room environment conditions: basalt amendment, B. subtilis amendment, and combined.
Results indicated that B. subtilis increased leachate Fe content in the absence of basalt. Extraction of soil cations displayed that B. subtilis together with basalt, compared to just basalt amendment, increased soil Fe content but not soluble Fe. It also increased soil Ca and Mg content that originate from basalt, potentially increasing the weathering rate of basalt. On the other hand, soil CO2 respiration is elevated compared to just basalt amendment, which may have implications for carbon sequestration. Further investigation is necessary to assess the implications for carbon sequestration and the practical applications of B. subtilis and basalt amendment in sustainable agriculture, particularly in plant-soil systems.
