Biomass Quality Responses to Selection for Increased Biomass Yield in Perennial Energy Grasses

Perennial grasses are candidates for biomass cropping systems that are focused on providing a wide range of ecosystem services in addition to sustainable bioenergy production. Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) are two of the dominant grasses of the tallgrass prairie and both are candidates for development of multifunctional diverse production systems. Breeding programs for both species are aimed at increasing biomass yield as a mechanism of improving economic sustainability without increasing production costs. The objective of this study was to determine if long-term selection for increased biomass yield in these two species has had any adverse impacts on biomass quality, or the ability to convert biomass into bioenergy. Check cultivars and improved breeding populations of both species were evaluated for a wide range of biomass quality traits at 13 locations in the North Central and Northeastern USA, and a subset of these populations were also subjected to more intensive and detailed fermentation analyses. In general, lignin and ferulates either remained constant or decreased following selection for increased biomass yield in the various genetic pedigrees. These changes resulted in some increases in predicted ethanol production and in vitro digestibility. The prediction of increased digestibility was confirmed by higher glucose release by pretreatment and deconstruction of an advanced lowland population. However, bioreactor fermentations with two different biofuel-producing microbes showed no differences in ethanol production. Overall, these studies indicated that the improved switchgrass and big bluestem populations had greater biomass yields without significantly reducing biomass quality or conversion efficiency into ethanol, suggesting that selection can achieve increases in biomass productivity while maintaining consistent biomass quality.