We studied the impacts of heavy metal pollution on abundance and community composition as well as activity of denitrifiers in two paddy soils.In this study,the two rice paddies had been polluted for more than three decades from metal mining and smelter activities.Abundance and community composition were determined using the real-time PCR assay and denaturing gradient gel electrophoresis of nitrite reductase and nitrous oxide reductase gene amplicons(nirK and nosZ),while denitrifying activities were assessed by measuring potential denitrifier enzyme activity.We found that the community structure of both nirK and nosZ containing denitrifiers shifted under pollution in the two rice paddies.All the retrieved nirK sequences did not group into either α-or β-proteobacteria,while most of the nosZ species were affiliated with α-proteobacteria.While abundance of both nirK and nosZ was significantly reduced in the polluted soils at "Dexing"(with relatively higher Cu levels),these parameters did not change significantly at "Dabaoshan".Furthermore,total denitrifying activity and N2O production and reduction rates also only decreased under pollution at "Dexing".These findings suggest that nirK and nosZ containing denitrifier populations and their activities could be sensitive to considerable Cu pollution,which could potentially affect N2O release from polluted paddy soils.