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Increasing the diversity of lignocellulosic feedstocks accepted by a regional biorefinery has the potential to improve the environmental footprint of the facility; harvest, storage, and transportation logistics; and biorefinery economics. However, feedstocks can vary widely in terms of their biomass yields and quality characteristics (chemical composition, moisture content, etc.). To investigate how the diversity of potential biofuel cropping systems and feedstock supply might affect process and field‐scale ethanol yields, we processed and experimentally quantified ethanol production from five different herbaceous feedstocks: two annuals (corn stover and energy sorghum) and three perennials (switchgrass, miscanthus, and mixed prairie). The feedstocks were pretreated using ammonia fiber expansion (AFEX), hydrolyzed at high solid loading (~17%–20% solids, depending on the feedstock), and fermented separately using microbes engineered to utilize xylose: yeast (Saccharomyces cerevisiaeY128) or bacteria (Zymomonas mobilis8b). The field‐scale ethanol yield from each feedstock was dependent on biomass quality and cropping system productivity; however, biomass yield had a greater influence on the ethanol yield for low‐productivity crops, while biomass quality was the main driver for ethanol yields from high‐yielding crops. The process ethanol yield showed similar variability across years and feedstocks. A low process yield for corn stover was determined to result from inhibition of xylose utilization by unusually elevated levels of hydroxycinnamates (p‐coumaric and ferulic acids) in the untreated biomass and their acid and amide derivatives in the resulting hydrolyzate. This finding highlights the need to better understand factors that influence process ethanol yield and biomass quality. Ultimately we provide evidence that most feedstocks fall within a similar range of process ethanol yield, particularly for the more resistant strain Z. mobilis8b. This supports the claim that the refinery can successfully diversify its feedstock supply, enabling many social and environmental benefits that can accrue due to landscape diversification. Our investigation of experimental ethanol yields from five key herbaceous bioenergy feedstocks (corn stover, energy sorghum, switchgrass, miscanthus, and mixed prairie) showed that biorefineries can successfully diversify their feedstock supply, enabling many social and environmental benefits due to landscape diversification. Field‐scale ethanol yields from each feedstock were dependent on biomass quality and cropping system productivity, while process ethanol yields showed similar variability across years and feedstocks and were related to effective utilization of biomass sugars during fermentation. Based on our results, there is a need to better understand factors that influence process ethanol yield and biomass quality. [ABSTRACT FROM AUTHOR]

Background: Interannual variability in precipitation, particularly drought, can affect lignocellulosic crop biomass yields and composition, and is expected to increase biofuel yield variability. However, the effect of precipitation on downstream fermentation processes has never been directly characterized. In order to investigate the impact of interannual climate variability on biofuel production, corn stover and switchgrass were collected during 3 years with significantly different precipitation profiles, representing a major drought year (2012) and 2 years with average precipitation for the entire season (2010 and 2013). All feedstocks were AFEX (ammonia fiber expansion)-pretreated, enzymatically hydrolyzed, and the hydrolysates separately fermented using xylose-utilizing strains of Saccharomyces cerevisiae and Zymomonas mobilis. A chemical genomics approach was also used to evaluate the growth of yeast mutants in the hydrolysates. Results: While most corn stover and switchgrass hydrolysates were readily fermented, growth of S. cerevisiae was completely inhibited in hydrolysate generated from drought-stressed switchgrass. Based on chemical genomics analysis, yeast strains deficient in genes related to protein trafficking within the cell were significantly more resistant to the drought-year switchgrass hydrolysate. Detailed biomass and hydrolysate characterization revealed that switchgrass accumulated greater concentrations of soluble sugars in response to the drought and these sugars were subsequently degraded to pyrazines and imidazoles during ammonia-based pretreatment. When added ex situ to normal switchgrass hydrolysate, imidazoles and pyrazines caused anaerobic growth inhibition of S. cerevisiae. Conclusions: In response to the osmotic pressures experienced during drought stress, plants accumulate soluble sugars that are susceptible to degradation during chemical pretreatments. For ammonia-based pretreatment, these sugars degrade to imidazoles and pyrazines. These compounds contribute to S. cerevisiae growth inhibition in drought-year switchgrass hydrolysate. This work discovered that variation in environmental conditions during the growth of bioenergy crops could have significant detrimental effects on fermentation organisms during biofuel production. These findings are relevant to regions where climate change is predicted to cause an increased incidence of drought and to marginal lands with poor water-holding capacity, where fluctuations in soil moisture may trigger frequent drought stress response in lignocellulosic feedstocks. [ABSTRACT FROM AUTHOR]