Soil bacterial and fungal communities respond differently to the biochar amendment in a cadmium-contaminated paddy field

For slightly and moderately cadmium (Cd)-contaminated paddy soils, in situ stabilization technologies such as biochar amendment provide a sustainable way of safe agricultural production. A two-year study was conducted to investigate soil microbial communities responses to biochar amendment in a slightly Cd-contaminated paddy field. Soil Cd fractions, organic carbon content, microbial communities, and their relationships were analyzed. The results showed that biochar application decreased Cd accumulation in brown rice by 13.56-24.56% and HOAc-soluble Cd content by 35.65-52.5%. It mainly induced the transformation of soluble Cd to oxidizable and residual Cd. Soil organic carbon (TOC), total nitrogen (TN), available potassium (AK) and available phosphorus (AP) contents tended to increase with biochar amendment. Biochar application significantly increased bacterial diversity but had no significant effect on fungal diversity. Soil oxidizable Cd contents were the most influencing environmental factors of bacterial communities, whereas soil pH were the most influencing environmental factors of fungal communities. These results indicate that the fungal community structure was influenced mainly bychanged soil pH, whereas the bacterial community structure was influenced by biochar application mainly due to Cd immobilization.