Effects of different types of biochar on vegetation growth, yttrium morphology, and microbial characteristics in the ionic rare earth mining areas

ong with the increasing demand for rare earths, ionic rare earth mining areas have caused a number of serious environmental problems. Biochar has become a research focus due to its advantages of containing a large number of pores, numerous functional groups and a large specific surface area. However, little is known about what type of biochar is helpful for mine soil remediation. Therefore, Addition of rice husk biochar (RHBC), pig manure biochar (PMBC) and sludge biochar (SDBC) paired with Euphrasia pectinata Ten. (EPT) and Astragalus sinicus L. (ASL) for pot experiments. After 90 days, PMBC-added treatments showed the best improvement in soil physicochemical properties, effectively alleviating soil acidification and increasing soil organic matter. Meanwhile, PMBC also significantly increased the dry weight and length of plants, which particularly favored the increase in dry weight of EPT. However, SDBC caused the soil pH to decrease and the dry weight of both plants to decrease significantly, which was unfavorable for mine rehabilitation. The addition of biochar reduced the diversity and abundance of bacteria and archaea, reduced the complexity of the network, and resulted in reduced interactions between bacteria and archaea. Biochar addition increased the relative abundance of two phyla, Proteobacteria and Actinobacteriota, which was crucial for rebuilding the symbiotic network, suggesting that they may play an important role in maintaining the stability of the network. The results of the study are informative for the selection of biochar for the remediation of ionic rare earth mining soils.