Effect of drought on composition and bioconversion for Miscanthus, mixed perennial grasses, and switchgrass as bioenergy feedstocks

A diverse portfolio of biomass feedstocks are being considered to achieve volume demands and competitive costs necessary for a bioenergy industry. Quality and variability become increasingly important as the range of feedstocks used for bioenergy broadens. Environmental factors during plant growth are a source of variation that can impact quality of biomass entering a bioconversion process. Drought conditions in 2012 were some of the most extreme in recent U.S. history. Drought has been linked to lower structural sugars for Miscanthus, mixed perennial grasses, and corn stover. This could have economic impacts, particularly when compounded with losses in dry biomass yield during drought. Our objective was to determine how drought impacts biomass composition and sugar yields from dilute-acid pretreatment (DAPT) and enzymatic hydrolysis. The study included Miscanthus, mixed perennial grasses, and switchgrass from Nebraska, Missouri, and Oklahoma, respectively. Samples were grown in a year without drought (2010) and a year with drought (2012). Drought stress indicators, including water and ethanol extractives, non-structural glucose, and proline, were greater in 2012 compared to 2010 for Miscanthus; however, these differences were not observed for switchgrass and only proline was greater in 2012 for mixed grasses. Reactivity and sugar yields from DAPT and enzymatic hydrolysis were significantly greater in 2012 compared to 2010 for Miscanthus, but only xylan yield was greater in the drought year for mixed grasses. Drought impacts on composition and sugar yields appear feedstock specific, likely due to variation in tolerance of each plant species to drought.