ABSTRACT
Chow et al. (2003) reported that nearly all (~95%) of the global energy market [370 exajoules of energy per year is equivalent to approximately 170 million barrels of oil per day or about 11.73 TW per hour (Chow et al. 2003; Somerville 2007)] comes from fossil fuels. The International Energy Agency (IEA) also suggested that the use of plant biomass could meet approximately one-third of the energy demands in Africa, Asia, and Latin America, and up to 80-90% in the poorest countries of these regions (Chow et al. 2003; Somerville 2007). According to a recent estimate by Somerville (2007), biofuels currently supply approximately one-tenth of all human energy consumption. The net CO2 assimilation by land plants per year is approximately 56 × 109 t (Field et al. 1998; Pauly and Keegstra 2008), and the biomass production by land plants worldwide is 170-200 × 109 t (Lieth 1975; Pauly and Keegstra 2008). Approximately three-fourths of this quantity is estimated to be plant cell wall biomass (Duchesne and Larson 1989; Poorter and Villar 1997; Pauly and Keegstra 2008). Currently, humans use only a negligible part (~2%) of plant cell-wall-based biomass in the form of wood for heat production, timber for building materials, pulp in the paper industry (Fenning and Gershenzon 2002; Pauly and Keegstra 2008), and as raw material in the textile industry. Moreover, plant cell-wall-based biomass does not serve as food for animals and humans to the extent that starch does. Therefore, interest in using this plant cell wall biomass resource as a material for biofuels has increased substantially in recent years (Schubert 2006; Pauly and Keegstra 2008).
