Rice is the largest grain crop in China,and its unique flooded paddy soil provides necessary condition for the occurrence of denitrification.However,the problems of nitrogen utilization decline and greenhouse gas emissions caused by denitrification have gained increasing concern.As a biological process driven by microorganisms,denitrification is affected by many factors such as soil pH and organic carbon sources.To reveal the effect of exogenous organic carbon on the functional activity and potential of denitrifying microorganisms in paddy soils with different pH values,this study added glucose to two paddy soils with different initial pH values and analyzed the abundance of key functional genes (nirK/S,nosZ) for denitrification at DNA and RNA levels.The results showed that the glucose reduced soil pH,the degree of which rose with the increase of the glucose concentration.The added glucose also enhanced soil denitrification,which was observed only in alkaline paddy soil.The responses of number and expression of nirK and nirS genes to glucose addition were significantly different between the two soils with different pH values,and the response degree of nirK gene was relatively higher.In acidic paddy soil,the number and expression of nosZ gene decreased with the increase of carbon source concentration;while in alkaline paddy soil,low concentration glucose significantly stimulated the number and expression of nosZ gene,but high concentration glucose caused soil acidification,which then inhibited the number and expression of nosZ gene.This study shows that exogenous organic carbon source affects the function and activity of denitrifying microorganisms in paddy soil from aspects of carbon source supply and soil acidification,which in turn influences the occurrence of denitrification and subsequent nitrous oxide emission.