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

Abstract

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.