Bioaugmentation potential of a cold-adapted and nitrate-reducing fungus to enhance nitrate removal in woodchip bioreactors

Abstract

Woodchip bioreactors are a promising approach to remove nitrate from agricultural drainage systems; however, their low removal efficiency at cold temperatures remains a significant challenge. Here we analyzed the efficacy of fungal inoculation to enhance nitrate removal in woodchip bioreactor microcosms under cold conditions. Among the cold-adapted, nitrate-reducing, and cellulose-degrading fungi previously isolated from soil, we identified Linnemannia hyaline strain SCG-10 as the fastest nitrate reducer. Inoculation of this fungal strain enhanced the rates of nitrate reduction, N2 production, and dissolved organic carbon production in woodchip bioreactor microcosms at 5 °C. Production of N2O was minor (<1%) in this study most likely due to the enhanced activity of N2O reducers by labile carbon. Quantitative PCR for nitrogen cycle-related genes showed the active transcription of both fungal and bacterial denitrification genes. These results suggest that inoculating cold-adapted, nitrate-reducing, and cellulose-degrading fungi is a promising approach to remove nitrate from agricultural fields under cold conditions.