Spartina alterniflora invasion impacts denitrifying community diversity and functioning in marsh soils

•Total, bacterial and fungal denitrification rates increased following Spartina invasion.•Spartina invasion increased denitrifying bacterial richness, evenness, α- and β-diversities.•Spartina invasion only increased denitrifying fungal richness and β-diversity.•Denitrifying bacterial community composition was closely related to denitrification rates.•Denitrifying fungal community composition was not related to denitrification rates.