IMPROVED FORAGE AND BIOENERGY PLANTS AND TECHNOLOGIES FOR THE CENTRAL USA
Location: Grain, Forage & Bioenergy Research
Title: Ethanol yields and cell wall properties in divergently bred switchgrass genotypes
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 2011
Publication Date: July 29, 2011
Citation: Sarath, G., Dien, B.S., Saathoff, A.J., Vogel, K.P., Mitchell, R., Chen, H. 2011. Ethanol yields and cell wall properties in divergently bred switchgrass genotypes. Bioresource Technology. 102:9579-9585.
Interpretive Summary: Switchgrass is a leading perennial lignocellulosic bioenergy species with significant potential for conversion to liquid transportation fuels such as ethanol. Lignin is one of the major constituents of plant cell walls and negatively impacts recovery of sugars and subsequently ethanol from the other cell wall components, namely hemicellulose and cellulose. Switchgrass plants from two related populations that differed significantly for biomass lignin concentration were analyzed for ethanol yield, lignin concentration and composition, other biomass constituents, and plant anatomy. Lignin concentration accounted for about 50% of the variation in ethanol yield indicating that other plant factors including plant anatomy and cell wall structure affected ethanol yields providing additional opportunities to improve liquid fuel yields from biomass.
Genetic modification of herbaceous plant cell walls to increase biofuels yields from harvested biomass is a primary bioenergy research goal. The focus of much of this research has been on cell wall lignin concentration. Using switchgrass genotypes developed by divergent breeding for ruminant digestibility which also genetically altered lignin concentrations, we demonstrate that other factors contribute to differences in ethanol yields from switchgrass biomass. Tissue from field grown, replicated switchgrass genotypes representing the extremes for in-vitro dry matter digestibility (IVDMD), from two populations recurrently bred for increased (T3) or decreased (T-1) digestibility were used in a multi-factor analyses which included plant anatomy. Low lignin (LL T3) plants significantly (39.1 %) out yielded the high lignin (HL T-1) plants for conversion to ethanol and extraction of xylans (12 %). Across all plants, the variation in ethanol yields attributable to differences in lignin concentration was only 46 % underscoring the influence of other tissue and cell wall factors. Stem cell wall phenolics, including phenolic acid esters and lignin monomer composition were generally different between the two populations, although there was no clear trend with respect to ethanol conversion. In contrast, improving IVDMD decreased the extent and apparent lignification of the cortical sclerenchyma and fiber sheaths. Scanning electron microscopy revealed that cell walls from untreated stems were smoother in plants with improved ethanol yields, and showed decreased granularity upon dilute acid pretreatment. Overall our results indicate that genetically modifying herbaceous plants to optimize ethanol recovery from biomass will require manipulating multiple aspects of plant wall and tissue composition.