Green plants are being used increasingly for production of transportation fuels in Europe and their application is being promoted through different European directives, which aim to achieve 20% of liquid fuel supply by 2020.
However with current energy productivity per hectare, the 2010 target would already require an acreage that is significantly higher than land set aside by the EU-15. More significant contributions to European energy demand therefore require much more efficient rates of conversion from plants on a limited land resource and it is recognised that this will require a step-change in our understanding and manipulation of plant traits and the large-scale use of second generation crops that are dedicated to energy production and not required for food.
Cellulosic biomass, also called lignocellulosic biomass, is a complex composite material consisting primarily of cellulose and hemicellulose (structural carbohydrates) bonded to lignin in plant cell walls. Liquid fuels derived from cellulosic biomass (the fibrous, woody, and generally inedible portions of plant matter) offer an important alternative to conventional energy sources to reduce Europe’s dependence on fossil fuels since they are potentially carbon-neutral, sustainable, low input and offer opportunities for enhanced biodiversity and less intensive land management.
Trees are attractive as a bioenergy system because they display a wide range of growth habits and can be grown on marginal lands unsuited to other agricultural crops including energy grasses, with reduced input costs and optimised land management. Within the forest action plan, the European Commission promotes the use of forest biomass for energy generation. Trees represent a domestic, renewable resource of raw material for generation of liquid transportation fuels. Moreover, using wood as an energy source can help to mitigate climate change by substituting fossil fuel, improving energy self-sufficiency, enhancing security of supply and providing job opportunities in rural areas. Such fuels can be used readily by current-generation vehicles and distributed through the existing transportation-fuel infrastructure.
Central to energizing a new biofuel industry based on conversion of cellulosic biomass to ethanol is to improve the quality and quantity of biomass feedstock. Current methods to break down biomass into simple sugars and convert them into ethanol are inefficient and constitute the core barrier to producing ethanol at quantities and costs competitive with gasoline.
Thus high biomass production needs to be combined with desirable cell wall properties in trees to be used as a source for generation of biofuels and with traits required for high nutrient and water use efficiency. In order to achieve this goal, a better fundamental understanding of gene networks and regulatory mechanisms that control growth, carbon and nitrogen allocation, and lignocellulosic quality and breakdown in trees is essential.