Nitrite-dependent anaerobic oxidation decreases methane emissions from peatlands

Peatlands are C-rich but N-poor ecosystems that function as an important C sink but also as significant CH4 sources and thus contribute to global warming. To confirm that N fertilization strongly reduces peatland CH4 emissions by stimulating nitrite-dependent anaerobic methane oxidation (n-damo), we investigated CH4 efflux and concentration in the soil profiles of a peatland subjected to long-term N fertilization. Contrary to previously reported increase of CH4 emissions from paddy, forest and grassland soils, N fertilization of peatland reduced CH4 efflux by 87%, especially during the hottest summer months (from 3.8 mg m−2 h−1 in the unfertilized control to 0.5 mg m−2 h−1 in the N-fertilized site). The CH4 efflux was strongly reduced because the high organic matter content of the peat indirectly stimulated n-damo by providing CH4 (methanogens use organic matter to produce methane) and nitrite (denitrifiers use organic matter as an energy source). N fertilization reduced the CH4 concentration by 50–95% (from 7800–9500 ppm in the unfertilized control to 370–4800 ppm in the N-fertilized site) in the top 30-cm soil, whereas the abundance of Methylomirabilis bacteria increased for 170% and its activity raised for 220% compared to the unfertilized control soil. Consequently, the topsoil is a hotspot of Methylomirabilis activity that use NO2 − to oxidize CH4 and play an important role in reducing CH4 emissions in N-fertilized peatlands.