Interaction effects of different chemical fractions of lanthanum, cerium, and fluorine on the taxonomic composition of soil microbial community.

The extensive mining of bastnasite (CeFCO₃) has caused pollution of lanthanum (La), cerium (Ce), and fuorine (F) in the surrounding farmland soil, severely threatening the safety of the soil ecosystem. However, the interaction effects of various chemical fractions of La, Ce, and F on the composition of microbial communities are unclear. In our study, high-throughput sequencing was performed based on the pot experiments of four types of combined pollution soils, i.e., La + Ce (LC), Ce + F (CF), La + F (LF), and La + Ce + F (LCF), and the pollution concentration ranges of these three elements of 20-240, 40-450, and 150-900 mg kg^-1, respectively. The improved Tessier method was used to investigate the interaction effects of chemical fractions of these elements on the variations in the soil microbial compositions. The result showed the residual form of La (La_RES) displayed restraint on Abditibacteriota, leading to its undetected level in the highest concentration of LC-polluted soils, whereas promoted relative abundance of microbes (Planctomycetota, Elusimicrobiota, Gemmatimonadota, and Rozellomycota) by more than 80%; the exchangeable and organic-bound forms of Ce and F as well as the iron-manganese-bound and residual forms of F were identified as the stress factors for the sensitive bacteria (e.g., WS4, Elusimicrobiota, RCP2-54, and Monoblepharomycota) in CF-polluted soils; in LF-polluted soils, the water-soluble form of La showed the most toxic effect on RCP2-54, Nitrospirota, and FCPU426, leading to decreased relative abundance by more than 80%; while La_RES and iron-manganese-bound form of F were identified as the stress factors for the relative abundance of Nitrospirota, Elusimicrobiota, and GAL15, showing decline of more than 80% in LCF-polluted soils. Our study revealed both inhibition and promotion effects of the element interaction on the growth of microbial communities, providing a certain experimental evidence to support further exploration of the treatment of environmental pollution caused by these elements.