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The immobilization of co-contaminants of organic and inorganic pollutants by biochar is an efficient remediation strategy.However,the effect of biochar amendments on the bioaccessibility of the co-contaminants in dry versus flooded soils has rarely been compared.In batch experiments,bamboo-derived biochar (BB) had a higher sorption capacity for phenanthrene (Phe)/pyrene (Pyr)/zinc (Zn) than c straw-derived biochar (CB),while CB had a higher sorption capacity for lead (Pb) than BB.After 150 days of incubation,the amendments of 2% CB,0.5% BB and 2% BB effectively suppressed the dissipation and reduced the bioaccessibility of Phe/Pyr by 15.65%/18.02%,17.07%/18.31% and 25.43%/27.11%,respectively,in the aerobic soils.This effectiveness was more significant than that in the anaerobic soils.The accessible Zn/Pb concentrations were also significantly lower in the aerobic soils than in the anaerobic soils,regardless of treatments.The Gram-negative bacterial biomass and the Shannon-Weaver index in the aerobic soil amended with 2% CB were the highest.The soil microbial community structure was jointly affected by changes in the bioaccessibility of the co-contaminants and the soil physiochemical properties caused by biochar amendments under the two conditions.Therefore,dry land farming may be more reliable than paddy soil cultivation at reducing the bioaccessibility of Phe/Pyr/Zn/Pb and enhancing the soil microbial diversity in the short term.