Effects of plant species, carbon and nitrogen amendments and pH on potential fungal denitrification in constructed wetlands

Objectives To provide guidelines for controlling fungal denitrification in constructed vertical flow wetlands, some factors affecting the fungal denitrification were investigated.Methods Four monocultured treatments were set up using four macrophyte species (Iris pseudacorus, Canna glauca, Scirpus validus and Cyperus alternifolius) in twenty simulated vertical flow constructed wetlands. After wetlands were operated for five months, fine sand samples were collected from 0-30 cm depth of wetlands, and effects of carbon and nitrogen amendments and pH gradient on potential fungal denitrification were tested using a room-incubating method.Results The two-way ANOVA (analysis of variance) indicated that the interactions between carbon or nitrogen amendments and plant species did not significantly affect the potential fungal denitrification (P 0.05), while the interactions between environmental pH and plant species significantly affected the potential fungal denitrification (P 0.05). Among seven carbon compounds, applications of both glucose and sodium succinate mostly improved the potential fungal dentrification in the wetland filled materials (P 0.05), whereas among four nitrogen compounds, sodium nitrite was the best nitrogen compound in enhancing the potential fungal denitrification (P 0.05). Compared with the treatments unamended with acid or alkaline, the treatment with pH 2.8 significantly decreased the potential fungal denitrification, whereas the treatments with pH 5.6 or 8.4 significantly increased the potential fungal denitrification to different extents.Conclusions The study highlights the importance of glucose, succinate and nitrite in enhancing the fungal denitrification potential, and the pH range of 5.6 to 8.4 for active fungal denitrification.