The access and recycling of the base cations are essential processes for the long-lasting functioning of forest ecosystems. While the role of soil bacterial communities has been demonstrated in mineral weathering and tree nutrition, our understanding of the link between the availability of base cations and the functioning of these communities remains limited. To fill this gap, we developed a microcosm approach to investigate how an increase in key base cations (potassium or magnesium) impacted the taxonomic and functional structures of the bacterial communities. During a 2-month period after fertilization with available potassium or magnesium, soil properties, global functions (metabolic potentials and respiration) as well as mineral weathering bioassays and 16S rRNA amplicon pyrosequencing were monitored. our analyses showed no or small variations in the taxonomic structure, total densities and global functions between the treatments. In contrast, a decrease in the frequency and effectiveness of mineral weathering bacteria was observed in the fertilized treatments. Notably, quantitative PCR targeting specific genera known for their mineral weathering ability (i.e., Burkholderia and Collimonas) confirmed this decrease. These new results suggest that K and Mg cation availability drives the distribution of the mineral weathering bacterial communities in forest soil. Understanding how microorganisms adapt to variations in resource availability is a central question in ecology and evolutionary biology. For plants, different behaviours related to the competition for resources have been described, such as competitors, which adapt to rapidly consume available resources, stress tolerators, which persist in nutrient-poor environments, and ruderals, which adapt to disturbances 1. These different competitive strategies as well as the related theories have been applied to the analysis of environmental microbial communities 2-4. However, most of the studies dealing with this question have focused on organic nutrients (C, N, S) or iron. The important role of the composition, quality and recalcitrance of organic carbon compounds in the regulation of the composition of microbial communities has been demonstrated in several aquatic and terrestrial environments 5-7. Similarly, the form of nitrogen (i.e., ammonium, nitrate, nitrite, amino acids) is known to strongly impact the composition and functioning of microbial communities 8,9. As an example, N application is known to modify the abundance of nitrifiers and denitrifiers 10 or methanotrophs 11. For most of these substrates, the presence and increasing concentrations of compounds directly select microorganisms capable of consuming them or having a better affinity. In contrast, the absence or decreasing concentrations of certain substrates, such as iron, are known to allow the selection of competitive taxa capable of mobilizing those nutrients through the production of sidero-phores and the regulation of their production 11-13. Comparatively, the relative impact of base cations on the soil bacterial communities at both the taxonomic and functional levels has been poorly investigated. Base cations correspond to inorganic compounds, also termed mineral nutrients or inorganic nutrients, such as potassium (K), magnesium (Mg) or calcium (Ca), which act as nutrients, co-factors, or structural components