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.