Ammonium loading disturbed the microbial food webs in biofilms attached to submersed macrophyte Vallisneria natans.

Abstract The knowledge about the impacts of ammonium loading on microbial food webs in biofilms attached to submersed macrophytes is limited. In the present study, Illumina sequencing method was employed to investigate bacterial and eukaryotic communities in biofilms attached to leaves of Vallisneria natans (V. natans) exposed to 1–16 mg L−1 NH 4 +-N for 10 days, and 8 mg L−1 NH 4 +-N for 21 days. Ammonium loading stimulated biofilms growth, enhanced the relative abundance of nitrifying genus Nitrospira and several denitrifying genera. Eukaryotic kingdom Metazoa, Viridiplantae, Chromista, Fungi and super group SARNU (Stramenopiles, Alveolata, Rhizaria, Nucleariidae and Fonticula group and unknown eukaryotes) were obtained. Relative abundance of Metazoa decreased with the increased ammonium concentration and exposure time. Redundancy analysis revealed that ammonium, dissolved oxygen (DO) and pH had a key role in determining microbial community structure. Network analyses revealed that there were complex interactions including feeding, parasitism and predatism among organism in biofilms, and the microbial food webs were disturbed by inhibiting metazoan growth but stimulating bacteria and algae growth. These results suggest that ammonium-disturbed microbial food webs in biofilms may contribute to the growth of biofilms and algae, and thus contribute to the decline of submersed macrophyte and provide "algal seeds" for the algae burst in water column. These data will be helpful in understanding the macrophytic region transform into algal region in water column polluted by ammonium. Graphical abstract Unlabelled Image Highlights • Ammonium increased relative abundances of nitrifiers and denitrifiers in biofilms. • Ammonium decreased relative abundance of Metazoa in biofilms. • Ammonium stimulated the growth of algae in biofilms. • Ammonium altered microbial food web in biofilms attached to leaves of plants. [ABSTRACT FROM AUTHOR]