Transforming a Demanding Goal into an Attainable Destiny: Use of Miscanthus as A Raw Material for Biomass

The United State’s Department of Energy and Department of Agriculture have recently focused their efforts on increasing biofuel production from biomass (Dohleman et al. 2009). The Departments’ goal to increase biomass production (and consequent biofuel production) will be more successful if an investigation first determines the most efficient raw material for the manufacturing of biomass. C4 grasses such as Miscanthus x giganteus (Miscanthus) and Panicum virgatum  (switchgrass) have particularly been targeted for their low anthropogenic inputs, higher net energy gains, and lower greenhouse gas emissions. The low anthropogenic inputs are partly attributable to the species’ symbiotic relationship with bacteria capable of nitrogen fixation, which diminish needs for nitrogen fertilizer, decreasing fossil fuel usage. Previous studies comparing Miscanthus and switchgrass have found that Miscanthus is more than two times as productive as switchgrass. — Alec Faggen 
Dohleman, F., Heaton, E., Leakey, A., Long, S., 2009. Does greater leaf-level photosynthesis explain the larger solar energy conversion efficiency of Miscanthus relative to switchgrass? Plant, Cell and Environment 32, 15251537

Dohleman and colleagues working at the University of Illinois and Iowa State University researched the hypothesis that this disparity in production can be attributed to Miscanthus’s higher leaf photosynthetic rates compared to switchgrass. The authors specifically investigated (1) leaf photosynthetic carbon dioxide (CO2) uptake under varying growing conditions; (2) the effectiveness of the plants’ water and nitrogen usage; and (3) energy loss during photosynthesis. This multi-phase study took place in central Illinois over 20 different days during 2005 and 2006, resulting in over 3300 recordings. The authors found that Miscanthus has a 33% higher leaf photosynthetic rate. In order to achieve this higher photosynthetic rate, Miscanthus must absorb higher levels of CO2 by opening its stomata more frequently and/or for longer durations of time. This increase in stomatal conduction, unfortunately, costs the Miscanthus a 25% loss of water.
The study explained the species’ higher leaf photosynthetic rate using various tests. The authors measured a 23% increase in whole-chain electron transport rate in Miscanthus compared to switchgrass. During transduction into whole chain electron transport, the authors found that light energy loss was significantly lower in Miscanthus. They also observed that leaf nitrogen and water use were significantly higher in Miscanthus. These findings all yield additional understanding as to the species’ higher photosynthetic rate.
These results, however, do not fully explain the higher productivity of Miscanthus. Other factors such as smaller root partitioning, decreased respiration, more extensive leaf canopy, and/or higher leaf area index must also contribute. Increased understanding as to the factors behind the greater productivity of Miscanthus will elucidate appropriate selection criterion for more successful biomass production. 

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