BIOCHAR AND BACILLUS AMYLOLIQUEFACIENS NS16 CAN INCREASE BIOMASS AND REDUCE CADMIUM ACCUMULATION OF PAKCHOI EXPLAINED BY CHANGES OF CADMIUM AVAILABILITY, MICROBIAL BIOMASS AND COMMUNITY IN THE RHIZOSPHERE SOIL

Inoculation of Bacillus may mediate plant growth and decrease uptake of heavy metals, but the combined effects and the mechanisms of Bacillus sp. and biochar on the cadmium availability and plant uptake are far less investigated. The effects of a plant growth-promoting B. amyloliquefaciens NS16, biochar, and their combination on the plant biomass and Cd accumulation in pakchoi and the mechanisms involved were characterized. Results showed that the biochar addition and NS16 inoculation, in combination or alone, significantly promoted plant biomass and decreased Cd uptake by plants with increased organic matter contents (by 13.2-44.5%) and increased microbial biomass carbon and nitrogen (by 6.9156.3%), and populations of bacteria and fungi (by 11.2-103%), and the decreased available Cd concentrations measured by DGT (by 13.2-44.5%), in the rhizosphere soils. Compared with the initial pH, the inoculation of NS16 did not affect the pH values significantly, while the treatments of biochar and biochar + NS16 increased that of the rhizosphere soil significantly. Results suggested that the alkalinized rhizosphere, promoted organic matter contents, enhanced microbial biomass and community, and decreased Cd availability may have contributed to the decreased Cd accumulation in plants under effects of biochar addition and NS16 inoculation.