Abstract: Through the enrichment of the active mud obtained from three chemical plants and the domestication with different concentration Ag⁺ solution,thirty bacteria strains with silver (Ag⁺)resistance were isolated,among which,the highest Ag^+_-resistant concentration was 80 mg·ml^-1.The plasmids in these bacteria were extracted,with the detection rate of 76.67％.The elimination rate of the plasmid in HAg4 bacteria was 98.75% by 40 mmol·L^-1 sodium benzoate,and 77.78% by 350 μg·ml^-1 acridine orange.It was suggested that the Ag⁺ -resistance of bacteria was highly correlated with their plasmids.

Key words: Natural forest, Pinus densiflora, Individual biomass, Stand density