Nitrous oxide production by the ectomycorrhizal fungi Paxillus involutus and Tylospora fibrillosa

Abstract

Nitrous oxide (N₂O) production by filamentous fungi has been demonstrated in pure culture and has been estimated indirectly in soils. However, it is unknown whether ectomycorrhizal fungi can also produce N₂O. We demonstrate for the first time the ability of nitrogen (N)-tolerant ectomycorrhizal fungi (Paxillus involutus and Tylospora fibrillosa), found in forest soils under moderate to high rates of N deposition, to produce N₂O from nitrate reduction. The N₂O concentrations from the ectomycorrhizal fungal treatments after a 10-day pure culture experiment were 0.0117±0.00015 (P. involutus) and 0.0114±0.0003 (T. fibrillosa), and 0.0114±0.00043 μmol N₂O L⁻¹ from a known fungal denitrifier (Fusarium lichenicola). No N₂O was detected in the control treatment. Our results indicate the potential for these two N-tolerant ectomycorrhizal fungi to contribute to N₂O production. Given that these species are abundant in many forest soils, the strength and regulation of fungal N₂O production should now be verified in situ.