Sustaining soil carbon in bioenergy cropping systems of northern temperate regions.

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Abstract Soil organic carbon (SOC) has an essential role in controlling ecosystem functions associated with soil physical, chemical and biological properties. Maintaining the SOC pool size in agroecosystems is important to sustain food security, protect soil biodiversity and buffer environmental impacts. The SOC pool is dynamic, with losses occurring due to CO 2 mineralization and gains from microbially mediated humification of organic substrates into stable C compounds. Bioenergy production from lignocellulosic feedstock implies that greater amounts of plant residues will be removed from agroecosystems and could deplete the SOC pool, based on empirical models and experimental results from long-term field trials. In northern temperate regions, several management practices are suggested to conserve the SOC pool, such as the application of biochar, judicious use of organic and inorganic fertilizers, crop rotations that include high biomass producing non-bioenergy crops or intercropping systems that combine perennial bioenergy crops with other crops (annuals or trees). Moreover, new technologies such as genetically modified (GM) bioenergy crops are recommended to enhance bioenergy production per unit energy input. Those modifications include GM crops with higher resource-use efficiency (i.e., for water, nutrients and light), GM crops with cellulase/ligninase enzyme systems for biofuel production and GM crops with higher calorific values that release more energy during combustion.