Structural and functional responses of soil fungal and bacterial communities to a lithium contamination gradient

The use of lithium (Li) in decarbonization strategies has positioned it as a central component of modern technological advances, particularly in battery applications. However, the increasing demand for Li has raised concerns about its environmental consequences, which are poorly documented. This study aimed to fill this knowledge gap by examining the impact of Li on soil bacterial/fungal communities. Using a microcosm approach, we explored the impacts of increasing Li concentrations on both microbial community structure and activities. Our results revealed significant changes in bacterial/fungal communities, particularly in the bacterial communities. Most of the indicator species were negatively correlated with the Li gradient, reinforcing the harmful effect of Li. Proteobacteria dominated at low concentrations, whereas Firmicutes were the most abundant at high concentrations. OTUs affiliated with the genus Alicyclobacillus represented >29 % of the total affiliated OTUs at the highest Li concentrations. Moreover, Alicyclobacillus fastidiosus showed resilience and specific adaptation to Li. Fungal communities showed less pronounced changes, with Mucoromycota remaining the dominant phylum at all concentrations. Nevertheless, some genera presented correlations with Li concentration, particularly the plant mutualists Leptodontidium, Oidiodendron, and Solicoccozyma. In addition, rapid decreases in several enzymatic activities crucial for the functioning of the carbon, nitrogen and phosphorus cycles were noted. Accordingly, microbial respiration was also impacted by high Li concentrations. Finally, a correlative analysis linked the decreases in enzyme activity to decreases in the abundances of both Proteobacteria and Ascomycota. These results underline the multiple impacts of Li on bacterial/fungal communities, highlighting both structural alterations and changes in microbial activities.