Effects of ammonium/nitrate ratios on plant growth and nitrogen and phosphorus removal in an ecological floating bed system

Ammonium/nitrate (NH4+-N/NO3−-N) ratios affect plant growth and development, yet their effects on plant growth and nitrogen and phosphorus removal in ecological floating bed (EFB) systems remain unexplored. This study investigated a pilot EFB system to assess and explores plant growth and nutrient removal efficiency under various NH4+-N/NO3−-N ratios. This study also examined how the NH4+-N/NO3−-N ratio affects nitrogen and phosphorus removal efficiency through analysis of the attached microbial community. Results showed that an NH4+-N/NO3−-N ratio of 2.6 increased the stem biomass of Juncus effusus by 442%. Additionally, the chemical oxygen demand (CODCr), nitrate nitrogen (NO3−-N), total nitrogen (TN), and total phosphorus (TP) removal efficiencies in the EFB system reached 68.9%, 79.4%, 74.6%, and 99.0%, respectively. Microbial community analysis indicated that at low NH4+-N/NO3−-N ratios, denitrifying bacteria (DNB) were dominant, whereas at higher ratios, nitrite–oxidizing bacteria (NOB) and heterotrophic nitrification–aerobic denitrification (HNADB) were more abundant. These findings suggest that the NH4+-N/NO3−-N ratio significantly affects nitrogen and phosphorus removal in EFB systems, corresponding changes in plant growth and microbial community composition.