Evaluation of greenhouse gas emissions in a Miscanthus sinensis Andersson-dominated semi-natural grassland in Kumamoto, Japan

Increasing greenhouse gas emissions from anthropogenic activities continue to be a mounting problem worldwide. In the semi-natural Miscanthus sinensis Andersson; grasslands of Aso, Kumamoto, Japan, which have been managed for thousands of years, we measured soil methane (CH₄) and nitrous oxide (N₂O) emissions before and after annual controlled burns. We estimated annual soil carbon (C) accumulation, and CH₄ and N₂O emissions induced by biomass burning in 2009 and 2010, to determine the impacts of this ecosystem and its management on global warming. Environmental factors affecting soil CH₄ and N₂O fluxes were unknown, with no effect of annual burning observed on short-term soil CH₄ and N₂O emissions. However, deposition of charcoal during burning may have enhanced CH₄ oxidation and N₂O consumption at the study site, given that emissions (CH₄: −4.33 kg C ha⁻¹ yr⁻¹, N₂O: 0.17 kg N ha⁻¹ yr⁻¹) were relatively lower than those measured in other land-use types. Despite significant emission of CH₄ and N₂O during yearly burning events in early spring, the M. sinensis semi-natural grassland had a large annual soil C accumulation, which resulted in a global warming potential of −4.86 Mg CO₂eq ha⁻¹ yr⁻¹. Consequently, our results indicate that long-term maintenance of semi-natural M. sinensis grasslands by annual burning can contribute to the mitigation of global warming.