Carbon sequestration in soil in a semi-natural Miscanthus sinensis grassland and Cryptomeria japonica forest plantation in Aso, Kumamoto, Japan
Although Miscanthus sinensis grasslands (Misc-GL) and Cryptomeria japonica forest plantations (Cryp-FP) are proposed bioenergy feedstock systems, their relative capacity to sequester C may be an important factor in determining their potential for sustainable bioenergy production. Therefore, our objective was to quantify changes in C accumulation rates 47 years after a Misc-GL was converted to a Cryp-FP. The study was conducted on adjacent Misc-GL and Cryp-FP located on Mt. Aso, Kumamoto, Japan.
... o, Kumamoto, Japan. After Cryp-FP establishment, only the Misc-GL continued to be managed by annual burning. Mass C and N, δ 13 C, and δ 15 N at 0 to 30 cm depth were measured in 5 cm increments. Carbon and N concentrations, C:N ratio, δ 13 C, and δ 15 N were measured in litter and/or ash, and rhizomes or roots. Although C input in Misc-GL by M. sinensis was approximately 36% of that in Cryp-FP by C. japonica, C accumulation rate in soil in Misc-GL (503 kg C ha -1 yr -1 ) was higher than that in Cryp-FP (284 kg C ha -1 yr -1 ). This was likely the result of larger C input from litter to soil, C quality (C:N ratio and lignin concentration in litter) and possibly more recalcitrant C (charcoal) inputs by annual burning. The difference in soil δ 15 N between sites indicated that N was better preserved and had greater cycling between plant, microbes, and soil in Misc-GL than in Cryp-FP. Our data indicate that in terms of soil C sequestration, biomass production with Misc-GL may be more advantageous than with Cryp-FP in Aso, Japan. 13 C/ 12 C or 15 N/ 14 N ratio of the PDB or atmospheric N 2 standards, respectively. Proportion of C (X C ) of C. japonica-derived C in the soil was calculated as follows using the method by Hansen et al. (2004) and Clifton-Brown et al. (2007): X C = (δ 13 C new-cryp -δ 13 C old ) / (δ 13 C cryp -δ 13 C old )