Influences of biochar with selenite on bacterial community in soil and Cd in peanut

Cadmium (Cd) pollution in crops seriously affects the ecosystem and human health. Effective measures should be employed to reduce the absorption and accumulation of cadmium in crops. Currently, there are many pieces of research on the application of biochar (BC) and selenium (Se) alone to the remediation of soil Cd pollution; however, few investigations have been devoted to the application of BC and Se together to the remediation of soil Cd pollution. The peanut was taken as the target crop to explore the effects of exogenous selenium and biochar on the remediation of soil Cd pollution. The response of the soil bacterial community to two levels of Cd concentration and its relationship with soil properties and Cd availability are methodically investigated. This study sets two cadmium pollution concentrations of low Cd (5 mg/ kg) and high Cd (20 mg/kg), as well as six treatments: blank, BC, soil Se, soil Se-BC, leaf Se, and leaf Se-BC. The achieved results revealed that both Se and BC could noticeably enhance the yield of peanut seeds and reduce the Cd content in peanut seeds. Among them, Se-BC treatment on soil exhibits the most influence, which reduces the Cd content by 47.86%. Se and BC also affect the physical and chemical properties of soil and remarkably magnify the content of soil available phosphorus, organic matter, soil pH, and soil conductivity. For instance, then effect is detected in the case of applying selenium biochar to soil, leading to an increase of about 64.38%, 72.62%, 2.64%, and 61.15%, respectively, and reducing the content of soil available cadmium by 21.02%. Redundancy analysis confirms that these properties enhance the abundance of dominant bacteria Actinobacteria, Proteobacteria, and Chloroflexi. The correlation analysis also indicates that Saccharimonadales, Bacillus, Arthrobacter, and other bacteria with the function of reducing the bioavailability of cadmium in soil reveal a considerable positive correlation with the variations of physical and chemical properties. In general, exogenous Se and BC incorporate to drop the content of available Cd in the soil through direct passivation, passivation caused by soil environmental change, and passivation caused by altering the soil microbial community structure; as a result, the migration and enrichment of Cd in peanut seeds are blocked and reduced. Moreover, the mixed application of BC and soil Se exhibits the best effect.