Nitrous oxide production by fungi in soils under different moisture levels

The production of nitrous oxide (N₂O) by facultative anaerobic fungi from the Fusarium, Trichoderma, and Paecylomyces genera was detected. Representatives of the genus Mucorales did not produce N₂O. The formation of N₂O in sterile soddy-podzolic soil inoculated by Fusarium oxysporum and F. solani increased significantly with the rise of the soil water content from 16-20% (50-60% of the field water capacity) to 30% (the field water capacity) with maximum values reached at the water content of 50% (the total soil water capacity). The production of N₂O by fungi at the soil water content of 50% was often higher under microaerobic conditions than under anaerobic conditions created via substitution of argon for atmospheric air in the flasks. The activity of N₂O production by fungi in the soil increased by several times upon nitrite or nitrate amendments. The specific activity of N₂ O formation in the soil was 0.38 ± 0.15 nmol N₂O/(h per mg) of dry mycelium. It was significantly lower than the rate of N₂O formation by Fusarium oxysporum 11dn1 in the nitrite-containing media and close to the rate of N₂O formation by this fungus in the nitrate-containing media. A comparison of the rate of N₂O release by active strain Fusarium oxysporum 11dn1 inoculated into the sterile soil with the rate of denitrification processes in the nonsterile soil showed that the contribution of soil fungi to the total emission of gaseous nitrogen compounds from the soil may reach 8% under optimum conditions.