Fungi significantly contribute to the nitrate reduction in woodchip bioreactors.
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Inoculation of nitrate-reducing fungi improves N removal under cold conditions.
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Fungi provide labile carbon to denitrifiers and perform fungal denitrification.
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Labile C provided by fungi can enhance N2O reduction to N2.
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Bioaugmentation with fungi is promising to remove nitrate from subsurface drainage.
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.
