13C abundance shows effective soil carbon sequestration in Miscanthus and giant reed compared to arable crops under Mediterranean climate

Many studies on soil organic carbon (SOC) sequestration in perennial biomass crops are available for Atlantic and continental environments of North Central Europe, while there is insufficient information for Southern Europe. Therefore, we assessed SOC turnover under Mediterranean climate, after a 9-year-old conversion from two annual crop systems, continuous wheat and maize/wheat rotation, to Miscanthus (Miscanthus sinensis×giganteus) and giant reed (Arundo donax), respectively. The naturally occurring 13C signature down to 0.60 m was used to evaluate the total amount of SOC in annual vs perennial species and to determine the portion of SOC derived from perennial species. Soil organic C was significantly higher under perennial (average, 91 Mg C ha−1) than annual species (average, 56 Mg C ha−1), with a stronger accumulation in the topsoil (0–0.15 m). This difference was consistent with reduced soil disturbance associated with perennial crop management. After 9 years of Miscanthus plantation, the amount of C4-derived C was 18.7 Mg ha−1, mostly stored at 0–0.15 m, whereas the amount of C3-derived C under giant reed was 34.7 Mg ha−1 and was more evenly distributed through soil depths, probably due to its deeper root apparatus. It is suggested that both Miscanthus and giant reed have a remarkable potential for SOC sequestration also under Mediterranean conditions, while supporting the growing bioenergy sector with biomass supply.