Nitrogen loading affects microbes, nitrifiers and denitrifiers attached to submerged macrophyte in constructed wetlands.

Submerged macrophytes and biofilms are important components of wetlands. However, little is known about the changes of microbes in biofilms attached to submerged macrophytes upon nitrogen loading. This study investigated the changes of microbes, algae, nitrifiers and denitrifiers in biofilms attached to the leaves of artificial plants (AP), Potamogeton malaianus (PM), Vallisneria natans (VN) and Hydrilla verticillata (HV) under varied initial concentrations of total nitrogen (TN). Nitrogen addition increased biofilm biomass and changed dissolved oxygen concentrations and pH values in overlaying water. Epiphytic algal densities showed the same trend at the same N level:AP>PM>VN>HV. As revealed by cluster analysis at phylum level, algae compositions in biofilm from four plants showed some host-specific at 2 and 12mgL-1 TN, but was clustered in the same group at 22mgL-1 TN regardless of plant species. Submerged macrophytes had better performance in total N removal than AP. In general, N application significantly increased the abundance of amoA, nirK, nirS, napA and cnorB in biofilm. The abundance of the denitrification genes (nirK, nirS, napA, narG and cnorB) was positively correlated with nitrogen application, while amoA was correlated with concentration of dissolved oxygen. These results indicate that N loadings stimulated the growth of biofilms attached to submerged macrophyte and the removal of total N can be partially ascribed to the synergistic interactions of submerged macrophyte and biofilms in wetlands. These results highlight the ecological role of submerged macrophyte-biofilm system in nitrogen removal in wetlands.