Long-Term Carbon Sequestration in Miscanthus Sinensis Grassland and Japanese Cedar (Cryptomeria japonica) Plantation in Aso, Japan.

Interest has increased worldwide in the generation of bioenergy from perennial crops to improve energy security and mitigate the effects of climate change. The objective of this study was to evaluate carbon (C) sequestration in Miscanthus sinensis (C₄ species) grassland and an adjacent Japanese cedar (Cryptomeria japonica, C₃ species) plantation established on Andisols in Aso, Kumamoto, Japan. M. sinensis, which is native to Japan, and is burned every spring, dominated both sites for more than 40 years, while C. japonica was planted 47 years ago. Over the 47-year period, aboveground biomass was notharvested in either site. In both sites, undisturbed soil was collected at 5-cm increments from the 0-30 cm depth, in addition to litter, roots, and/or rhizomes. Soil samples were analyzed for bulk density and C content and all samples were analyzed for δ¹³C. At the 0-5 cm soil depth, δ¹³C of the grassland was higher (-17‰) than that in the plantation (-21‰). C mass of this soil layer was also higher in the grassland (4.2 kg C m²) compared to the plantation (3.2 kg C m²). Assuming δ¹³C across sites was similar before C. japonica establishment, lower δ¹³C value at 0-5 cm of soil in the plantation might be due to low δ¹³C-C input from C. japonica. Estimated C accumulation at the 0-5 cm soil depth was 503 and 284 kg C ha^-1 yr^-1 in the grassland and plantation, respectively, indicating a rate of accumulation 1.8 times higher for M. sinensis than C. japonica. Even though burning occurred, which resulted in decreasing potential C input to the soil, it appears there is considerable potential for soil C accumulation, especially compared to an unburned woody C₃ crop. Cultivation of Miscanthus for bioenergy might offer more carbon-budget benefits than merely the renewable energy benefit often associated with this perennial crop.