Fungal denitrification contributes significantly to N2O production in a highly acidic tea soil

Previous studies have indicated fungi might contribute substantially to soil N2O production under the acidic conditions. Yet, the fungal contribution to N2O emission in an acidic tea soil has been rarely reported. The objectives of the present research were to determine the fungal and bacterial contribution to N2O emission and identify, characterize N2O-producing fungal isolates, and testify their ability in producing N2O via inoculating strains to the sterilized acidic tea soil. Two antibiotics (cycloheximide and streptomycin) combined with substrate-induced respiration (SIR) method were used in a microcosm experiment. Rose-Bengal medium was used to isolate the N2O-producing fungi. The active fungal strains were identified on the basis of 18S ribosomal DNA (rDNA) gene sequencing and then were inoculated into sterile soil and nonsterile soil in an incubation experiment. Fungal denitrification comprised 70% of N2O production in this tea soil. Two fungi, namely Penicillium and Hypocrea, were isolated from tea soils at the pH of 3.8. N2O emission from Penicillium strain was 328 mu g g(-1) biomass, showing at least two orders of magnitude greater than that of Hypocrea strain. The inoculation of Penicillium strain into sterile or nonsterile soils suggested a significant contribution of fungal denitrification to N2O production in the tea soil. The relative contribution of fungi in this study was more intensified than the reported studies, suggesting that denitrifying fungi might turn to be more tolerant and dominant in this acidic soil, thus resulting to greater fungal contribution to N2O production. Fungal denitrification might play an important role in N2O emission in this highly acidic tea soil. Our finding might help to predict N2O emissions from acidic soils and provoke practicable methods to mitigate soil N2O emissions.