Bioenergy Crops Compared: Miscanthus More Productive Than Switchgrass

Converting biomass into biofuels can be costly and slow. Two crops, both classified as C4 perennial grasses, have been studied extensively to determine how best to improve costs and production rates. Switchgrass (Panicum virgatum) has been trialed across the United States. Miscanthus (Miscanthus x giganteus) has been studied throughout the European Union. Both show great promise, but until now, nobody has been sure which crop is more efficacious. The study completed by Frank Dohleman of the Plant Biology Department at University of Illinois at Urbana-Champaign and his colleagues, is the first to compare the productivity of the two grasses in side-by-side field trials. Results from trials throughout Illinois show that Miscanthus is more than twice as productive as switchgrass.

Dohleman's team, which included Dafu Wang, Andrew D.B. Leakey & Stephen P. Long also of University of Illinois, along with Emily A. Heaton of Ceres Inc., theorized that Miscanthus produces more usable biomass than switchgrass because of these three key attributes:

1. Miscanthus can gain greater amounts of photosynthetic carbon per unit of leaf area

2. Miscanthus has a greater leaf area

3. Miscanthus has a longer growing season.

The research team measured the amount of gas exchanged on the upper canopy of Miscanthus leaves from pre-dawn to post-dusk on 20 dates in the 2005 and 2006 growing seasons. The averages from two years' data showed that Miscanthus gained 33% more carbon than switchgrass. Integrated measurements also showed that the Miscanthus leaf area was 45% greater than switchgrass and that Miscanthus plants grew an average of eleven days longer than switchgrass. This extended growing season and accompanying lower temperatures proved to further boost the photosynthetic activity of Miscanthus. Specifically, pyruvate Pi dikinase was found to be expressed at higher rates when ambient temperatures are lower. This enzyme supports C4 photosynthesis in Miscanthus.

Unraveling the mystery of why Miscanthus is the more productive crop will enable researchers to engineer this and other potential bioenergy crops. These developments will increase production options as well as support efforts within biofuel research and industry to work with non-food based biomass resources.