Characterization of soil microbial community activity and structure for reducing available Cd by rice straw biochar and Bacillus cereus RC-1.

The combination of biochar and specific bacteria has been widely applied to remediate Cadmium-contaminated soil. But little is known about how such composites affect the dynamic distribution of metal fractions. This process is accompanied by the alternations of soil properties and microbial community structures. Composite of rice straw biochar and Bacillus cereus RC-1 were applied to investigate its impacts on Cd alleviation and soil microbial diversity and structure. The bacterial/biochar composite treatment decreased the fraction of HOAc-extractable Cd by 38.82%, and increased residual Cd by 23.95% compared to the untreated control. Moreover, compared with the untreated control, the composite treatment significantly increased the soil pH by about 1.5 units, and the activities of catalase, urease and invertase enzymes were increased by 42.39%, 30.50% and 31.20%, respectively. Composite treatment increased soil bacterial and fungal alpha diversity, the relative abundance of Bacillus, Streptomyces, Arthrobacter, and Aspergillus species were also increased. Mantel test and correlation analysis indicated that the effects associated with fungal communities in influencing soil properties were lower than that those of bacterial communities by different treatment. Aggregated boosted tree (ABT) models analysis showed that soil chemical proprieties (as determined by SOM, CEC, AN, etc.,) contributed over 50% of the changes in bacterial and fungal communities by the composite treatment. The co-occurrence network results showed that all treatments enhanced the correlation between OUT groups and improved the possible relationships in the bacterial and fungal communities, especially the interrelationships between bacteria and fungi after the Cd fractions stabilized. These findings provide a new insight to optimal strategies for the remediation of Cd-contaminated soil.