Background
The authors write that "alfalfa (Medicago sativa L.) is one of the most important forage crops in Europe," and they say that it is also "widely distributed around the world and is highly persistent in comparison to most common field crops," citing Bagavathiannan and Van Acker (2009). In addition, they further note alfalfa's double importance, in that its stems can be used as a biofuel, while its leaves may be used as "a high-protein livestock feed supplement," citing the works of Delong et al. (1995) and Lamb et al. (2003).

What was done
Baslam et al. grew well watered and fertilized alfalfa seedlings in 2-L pots filled with a 2.5:2.5:1 mix of vermiculite:sand:light peat for four weeks, both with and without arbuscular mycorrhizal fungi (AMF) inoculation in greenhouse environments of two different CO2 concentrations (395 and 710 ppm).

What was learned
The five Spanish researchers report that "AMF-inoculated alfalfa plants exposed to elevated CO2 showed improved leaf, stem and root biomass, enhanced amount of hemicellulose and decreased concentration of lignin in cell walls of leaves as well as increased levels of glucose and fructose in stems."

What it means
"Together," in the words of Baslam et al., "these results indicate improved forage quality (leaves) and enhanced potential for bioethanol conversion (stems) in alfalfa associated with AMF and cultivated under high atmospheric CO2 concentration." And they add that "the potential of stems for producing CH4 reinforces their suitability for the conversion of biomass into bioethanol."

References
Bagavathiannan, M.V. and Van Acker, R.C. 2009. The biology and ecology of feral alfalfa (Medicago sativa L.) and its implications for novel trait confinement in North America. Critical Reviews in Plant Sciences 28: 69-87.

Delong, M.M., Swanberg, D.R., Oelke, E.A., Hanson, C., Onischak, M., Schmid, M.R. and Wiant, B.C. 1995. Sustainable biomass energy production and rural economic development using alfalfa as a feedstock. In: Klass, D.L. (Ed.) Second Biomass Conference of the Americas: Energy, Environment, Agriculture and Industry, National Renewable Energy Laboratory, Golden Colorado, USA, pp. 21-24.

Lamb, J.F.S., Sheaffer, C.C. and Samac, D. 2003. Population density and harvest maturity effects on leaf and stem yield in alfalfa. Agronomy Journal 95: 635-641.