Carbon sequestration under Miscanthus: a study of 13 C distribution in soil aggregates MARTA DONDINI *, KEES-JAN VAN GROENIGEN *, ILARIA DEL GALDO w and MICHAEL B. JONES * *Department of Botany, School of Natural Science, Trinity College Dublin, Dublin 2, Ireland, wDip. Scienze Ambientali, Seconda Universita ` di Napoli, via Vivaldi 43, 81100 Caserta, Italy Abstract The growing of bioenergy crops has been widely suggested as a key strategy in mitigating anthropogenic CO 2 emissions. However, the full mitigation potential of these crops cannot be assessed without taking into account their effect on soil carbon (C) dynamics. Therefore, we analyzed the C dynamics through four soil depths under a 14- year-old Miscanthus plantation, established on former arable land. An adjacent arable field was used as a reference site. Combining soil organic matter (SOM) fractionation with 13 C natural abundance analyses, we were able to trace the fate of Miscanthus- derived C in various physically protected soil fractions. Integrated through the whole soil profile, the total amount of soil organic carbon (SOC) was higher under Miscanthus than under arable crop, this difference was largely due to the input of new C. The C stock of the macroaggregates (M) under Miscanthus was significantly higher than those in the arable land. Additionally, the C content of the micro-within macroaggregates (mM) were higher in the Miscanthus soil as compared with the arable soil. Analysis of the intramicroaggregates particulate organic matter (POM) suggested that the increase C storage in mM under Miscanthus was caused by a decrease in disturbance of M. Thus, the difference in C content between the two land use systems is largely caused by soil C storage in physically protected SOM fractions. We conclude that when Miscanthus is planted on former arable land, the resulting increase in soil C storage contributes considerably to its CO 2 mitigation potential. Keywords: 13 C natural abundance, aggregates, C sequestration, Miscanthus, soil organic matter Received 2 May 2009; revised version received 15 July 2009 and accepted 18 August 2009 Introduction In recent years, climate change impacts and greenhouse gas (GHG) emissions from different forms of land use have emerged as key factors shaping agricultural poli- cies world wide. Whereas agriculture is one of the largest sources of anthropogenic GHG emissions, it also provides several possibilities for GHG mitigation (IPCC, 2001). Specifically, the conversion of surplus agricultural land to bioenergy crops provides great potential for CO 2 mitigation across Europe (Smith et al., 2000). Biomass energy is close to ‘carbon neutral’, that is to say, it produces energy while only releasing C to the atmosphere that has been captured during the growing cycle of the plant, rather than emitting C that has been locked away from the atmosphere in fossil reserves for millions of years. Bioenergy crops can take many forms and can be converted to a number of different products. Many crop species are multipurpose in that they can be used to produce more than one type of energy product (Sims et al., 2006). In recent years, Miscanthus (Miscanthus  giganteus Greef and Deu.) has received much attention as a potential bioenergy crop (Styles et al., 2007). This per- ennial rhizomatous grass, which is native to East Asian tropical and subtropical regions, has a considerable biomass production potential even under temperate climatic conditions (Lewandowski et al., 2000). Clifton- Brown et al. (2004) estimated peak annual yields across Europe ranging from 13 t ha 1 in Finland and Sweden to 25.8 t ha 1 in Belgium. By both displacing C released through burning fossil fuels and by soil C sequestration, growing Miscanthus for electricity production could Correspondence: Marta Dondini, tel. 1 353 1896 3068, e-mail: dondinim@tcd.ie GCB Bioenergy (2009) 1, 321–330, doi: 10.1111/j.1757-1707.2009.01025.x r 2009 Blackwell Publishing Ltd 321