Assessing the impacts of the establishment of Miscanthus on soil organic carbon on two contrasting land-use types in Ireland

In recent years the use of biomass for energy production has become an increasingly important measure for mitigating global change. However, the scientific debate has been inconclusive with regard to the risks and benefits of bioenergy use. There is particular concern that land-use change to bioenergy production can lead to increased CO2 emissions. These emissions result from the loss of vegetation and the soil disturbance. The use of Miscanthus x giganteus as a bioenergy feedstock offers a possible solution, as it shows a large soil carbon (C) sequestration potential. The aim of the present study was to analyse the impacts of land-use change to Miscanthus on soil fractions and associated soil organic carbon (SOC). Four young commercial Miscanthus sites, as well as adjacent sites representing the former land-use, in SE Ireland were analysed for changes in SOC stocks and newly sequestered Miscanthus-derived C. The fraction with which the SOC is associated significantly influenced its decomposability and turnover time. Using the C-13 natural abundance method, we found that newly sequestered C was found mainly as particulate organic matter (79.7% of Miscanthus-derived C) and therefore in a labile state with short turnover times. No significant differences were found in the distribution of the different soil fractions and SOC between the Miscanthus and the control sites, and it was shown that the share of fractions on the bulk soil as well as the proportion of the SOC associated with these fractions in young Miscanthus sites depends mainly on the previous land-use.