Invasive plant species as potential bioenergy producers and carbon contributors
In the United States, bioenergy sources are being investigated in an effort to reduce dependence on foreign oil and the associated risks to national security and climate change (Koh and Ghazoul 2008; Demirbas 2007; Berndes et al. 2003). Multiple sources of renewable plant-based material have been identified and include agricultural and forestry residues, municipal solid waste, industrial waste, and specifically grown bioenergy crops (Demirbas et al. 2009; Gronowska et al. 2009). These sources are most commonly converted to energy through direct burning, conversion to gas, or conversion to ethanol. Annual crops, such as corn (Zea Mays L.) and sorghum grain, can be converted to ethanol through fermentation, while soybean and canola are transformed into fatty acid methyl esters (biodiesel) by reaction with an alcohol (Demirbas 2007). Perennial grasses are one of the more viable sources for bioenergy due to their continuous growth habit, noncrop status, and multiple use products (Lewandowski el al. 2003). In addition, a few perennial grass species have very high water and nutrient use efficiencies producing large quantities of biomass on an annual basis (Dohleman et al. 2009; Grantz and Vu 2009).
Cellulosic bioenergy research is widespread throughout the country (figure 1) and has resulted in a proliferation of studies examining switchgrass (Panicum virgatum L.) in cropping systems (Sanderson et al. 2006). The major focus of current switchgrass research is on production and establishment (Bhandari et al. 2008; Brenner and Moore 2008; Butler et al. 2008; West et al. 2008), with other studies on the effects of switchgrass growth on carbon and nitrogen cycles (Parrish and Lemus 2008), diversity of species mixes containing switchgrass (Staggenborg and Propheter 2008), and the breeding/genetics of switchgrass biotypes (Samuels et al. 2008). In addition to switchgrass, research in the United States is being conducted on many other cellulosic crops, such as Miscanthus giganteus, hybrid poplar (Populus hybrids), and reed canarygrass (Phalaris arundinacea L.) (Sanderson and Adler 2008). To date, little research has been conducted on existing (noncultivated) bioenergy sources (e.g., invasive plant species) from noncrop agricultural land (e.g., marginal and riparian areas).