Nitrous Oxide Producing Fungi Isolated From Agricultural Soil.

Fungi generally dominate microbial biomass in various ecosystems; therefore fungi capable of N₂O production may have great implications to soil N₂O emission. This study was aimed at i) identifying N₂O-producing fungi in agricultural soil and ii) characterizing physiological responses of N₂O-producing fungus isolates to inorganic N form, pH, and oxygen availability. Soil samples were collected from 5 cropping systems: conventional farming, organic farming, integrated crop and livestock, plantation forestry, and abandoned agriculture field subjected to natural succession, located at the Center for Environmental Farming Systems, Goldsboro, NC. Fungi were isolated from the soil and tested for N₂O production in a nitrate-containing liquid Czapek medium. Streptomycin and cycloheximide were used as a bacterial and fungal inhibitor, respectively, to verify fungal N₂O production. A total of 80 N₂O-producing fungi were isolated, representing 17 genera and over 30 species. N. vasinfecta showed the highest capability of N₂O production, followed by F. oxysporum. Other fungus isolates of high N₂O production were A. oryzae, A. terreus, A. versicolor and P. pinophilum. Furthermore, 10 selected N₂O-producing fungus isolates were examined for nitrogen substrate and pH preferences, and O₂ requirements. Seven isolates had at least 65% greater N₂O production in a nitrite than a nitrate medium. The majority of isolates also showed greater N₂O production at neutral pH and 0% headspace O₂ conditions. Our results demonstrated that N₂O-producing fungi could be prevalent in agricultural systems and prefer different environments.