Salinity effect on denitrification efficiency with reed biomass addition in salt marsh wetlands

[Display omitted] •The nitrogen removal was improved at five salinities after reed biomass addition.•A salinity of 7‰ benefitted the release of organic matter from reed biomass.•The highest TN removal and lowest N2O emission were achieved at salinity of 7‰.•Salinity affected microbial community and genera of denitrification in wetlands. Five simulated salt marsh wetlands with reed were constructed to investigate the effect of salinity on denitrification efficiency and its enhancement by reed biomass addition. It was found that the salinity of 7 ‰ and 10 ‰ could promote the organic carbon release of reed biomass. Results showed that the nitrate removal was highest at the salinity of 7 ‰, and would be further enhanced from 54.06 ± 12.46 % to 74.37 ± 11.53 % after the addition of reed biomass. Meanwhile, the lowest nitrous oxide emission flux was also achieved, with 0.23 mg/(m2 h) at this salinity. Microbiological analysis showed that salinity changed the microbial community. The increasing salinity increased the relative abundance of Chloroflexi and Actinobacteria, but decreased that of Proteobacteria. Main functional genera of denitrification changed from Desulfuromonas to Azoarcus and Anaeromyxbacter when the salinity increased to 15 ‰. These results will help to understand the nitrogen removal capacity of salt marsh wetlands with reed biomass addition.