Effect of sulfur-iron modified biochar on the available cadmium and bacterial community structure in contaminated soils.

Cadmium contamination in paddy soils has aroused increasing concern around the world, and biochar has many positive properties, such as large specific surface areas, micro porous structure for the heavy metal immobilization in soils. However there are few studies on sulfur-iron modified biochar as well as its microbiology effects. The purpose of this study was to evaluate the Cd immobilization effects of sulfur or sulfur-iron modified biochar and its related microbial community changes in Cd-contaminated soils. SEM-EDX analysis confirmed that sulfur and iron were loaded on the raw biochar successfully. Sulfur-modified biochar (S-BC) and sulfur-iron modified biochar (SF-BC) addition increased pH value and the content of soil organic matter, and also decreased DTPA-extractable Cd. There was a negative significant correlation between organic matter content and the available Cd (P < 0.05). During a 45-d incubation period, the fractions of Cd are mainly with the exchangeable (25.16-35.79%) and carbonate (22.01-25.10%) fractions. Compared with the control, the concentrations of exchangeable Cd in soil were significantly (P < 0.05) decreased by 12.54%, 29.71%, 18.53% under the treatments of BC, S-BC, SF-BC respectively. The S-BC and SF-BC treatments significantly (P < 0.05) increased Chao1, observed, Shannon and Simpson diversity indices compared with the control and biochar treatments. Meanwhile, the relative abundance of Proteobacteria, Bacteroidetes, and Actinobacteria increased, whereas the abundance of Acidobacteria and Germmatimonadetes decreased. Capsule: Sulfur-modified and sulfur-iron modified biochar applications decreased the available Cd and changed the microbial community.