Impact of drought on composition and sugar yields from dilute-acid pretreatment and enzymatic hydrolysis of Miscanthus, mixed perennial grasses, and switchgrass

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.

The objective of this study 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). Water extractives, ethanol extractives, non-structural glucose, and proline were significantly greater in 2012 compared with 2010 for Miscanthus, indicating drought stress. Only proline was greater in 2012 for mixed grasses. Structural glucan and xylan from compositional analysis were significantly lower in 2012 for Miscanthus and mixed grasses. Reactivity and sugar yields from DAPT and enzymatic hydrolysis were significantly greater in 2012 compared with 2010 for Miscanthus, indicating that even if structural sugars decrease during drought sugar yields and reactivity may increase. For mixed grasses, only xylan yield was greater in the drought year. No differences were observed for switchgrass composition, sugar yields, and reactivity between 2010 and 2012. Drought impacts on composition and sugar yields appear feedstock specific, likely because of variation in tolerance of each plant species to drought.