Evaluation of Carbon Budget in a Natural Miscanthus Sinensis Grassland in Central Hokkaido, Japan.

Interest has increased worldwide in the generation of bioenergy from perennial crops to improve energy security and to mitigate the effects of greenhouse gases on climate change. Miscanthus sinensis has considerable potential as a biofuel crop. The goal of this study was to evaluate the carbon (C) budget of an approximately 35-yr-old M. sinensis natural grassland. This grassland is located on a drained Andisol, in central Hokkaido, Japan. Bare soil plots were created to measure soil organic matter (SOM) decomposition by carbon dioxide (CO₂) emissions. Methane (CH₄) emissions and C deposition were also measured. Aboveground net primary production (ANPP) and net ecosystem production (NEP) were calculated in natural grassland plots. Belowground net primary production (BNPP) could not be calculated accurately due to substantial inherent spatial variability in belowground biomass production and was assumed to be equal to decomposition of belowground biomass. ANPP of M. sinensis and other plant species present in the site was 1.1 and 1.7 Mg C ha^-1, respectively. Large amounts of C were stored belowground compared to ANPP. Average belowground biomass was 9.6 Mg C ha^-1. SOM decomposition was 2.3 Mg C ha^-1. CH₄ emission and C deposition were -1.1 and 3.3 kg C ha^-1, respectively. Although NEP was 451 kg C ha^-1, when above ground biomass was harvested, NEP was -2.3 Mg C ha^-1. These data suggest that this natural ecosystem could become a source of atmospheric C when biomass is harvested. However, because large amounts of biomass C were stored belowground, the actual C loss from this ecosystem might be less than what was calculated in the study.  Improved measurement of belowground biomass growth would allow for a more accurate calculation.