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 soil C sequestration 47 similar to 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. After Cryp-FP establishment, only the Misc-GL continued to be managed by annual burning every March. Mass C and N, d13C, and d15N at 030 similar to cm depth were measured in 5 similar to cm increments. Carbon and N concentrations, C:N ratio, d13C, and d15N 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, mean annual soil C sequestration in Misc-GL (503 similar to kg similar to C similar to ha-1 similar to yr-1) was higher than that in Cryp-FP (284 similar to kg similar to C similar to ha-1 similar to yr-1). This was likely the result of larger C input from aboveground litter to soil, C-quality (C:N ratio and lignin concentration in aboveground litter) and possibly more recalcitrant C (charcoal) inputs by annual burning. The difference in soil d15N between sites indicated that organic C with N had greater cycling between heterotrophic microbes and soil and produces more recalcitrant humus in Misc-GL than in Cryp-FP. Our data indicate that in terms of soil C sequestration, maintenance of Misc-GL may be more advantageous than conversion to Cryp-FP in Aso, Japan.