Fungal denitrification: Bipolaris sorokiniana exclusively denitrifies inorganic nitrogen in the presence and absence of oxygen

Fungi may play an important role in the production of the greenhouse gas nitrous oxide (N2O). Bipolaris sorokiniana is a ubiquitous saprobe found in soils worldwide, yet denitrification by this fungal strain has not previously been reported. We aimed to test if B. sorokiniana would produce N2O and CO2 in the presence of organic and inorganic forms of nitrogen (N) under microaerobic and anaerobic conditions. Nitrogen source (organic-N, inorganic-N, no-N control) significantly affected N2O and CO2 production both in the presence and absence of oxygen, which contrasts with bacterial denitrification. Inorganic N addition increased denitrification of N2O (from 0 to 0.3 μg N20-N h−1 g−1 biomass) and reduced respiration of CO2 (from 0.1 to 0.02 mg CO2 h−1 g−1 biomass). Isotope analyses indicated that nitrite, rather than ammonium or glutamine, was transformed to N2O. Results suggest the source of N may play a larger role in fungal N2O production than oxygen status. Inorganic nitrogen addition alters fungal denitrification and respiration in the presence and absence of oxygen.