NO3−/NH4+ ratios affect the growth and N removal ability of Acorus calamus and Iris pseudacorus in a hydroponic system

Sweet flag (Acorus calamus L.) and yellow flag (Iris pseudacorus L.) have been used increasingly in constructed wetlands (CWs) for treatment of eutrophic wastewater. In order to properly match plant species with the type of wastewater being treated, it is important to know the performance of plant species under different NO3−/NH4+ ratios. We investigated dry matter (DW) production and N content of A. calamus and I. pseudacorus under five NO3−/NH4+ ratios (100/0, 75/25, 50/50, 25/75, and 0/100) in a hydroponic system. Results showed that the two species exhibited different preferences for NO3− and NH4+. Total DW, shoot DW, and N content were greater with NO3−/NH4+ ratios of 50/50 and 75/25 than otherwise for A. calamus, but these parameters were only higher under the sole NO3− treatment in I. pseudacorus. We conclude that A. calamus could be best used for treating wastewater in constructed wetlands with NO3−/NH4+ ratios between 50/50 and 75/25, while I. pseudacorus for treating wastewater with NO3− only to achieve the highest biomass production and efficiency in the removal of N.