Kenneth P. Vogel

Net energy of cellulosic ethanol from switchgrass

Perennial herbaceous plants such as switchgrass (Panicum virgatum L.) are being evaluated as cellulosic bioenergy crops. Two major concerns have been the net energy efficiency and economic feasibility of switchgrass and similar crops. All previous energy analyses have been based on data from research plots (<5 m2) and estimated inputs. We managed switchgrass as a biomass energy crop in field trials of 3–9 ha (1 ha = 10,000 m2) on marginal cropland on 10 farms across a wide precipitation and temperature gradient in the midcontinental U.S. to determine net energy and economic costs based on known farm inputs and harvested yields. In this report, we summarize the agricultural energy input costs, biomass yield, estimated ethanol output, greenhouse gas emissions, and net energy results. Annual biomass yields of established fields averaged 5.2 -11.1 Mg·ha−1 with a resulting average estimated net energy yield (NEY) of 60 GJ·ha−1·y−1. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY than previous estimates from human-made prairies that received low agricultural inputs. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. This is a baseline study that represents the genetic material and agronomic technology available for switchgrass production in 2000 and 2001, when the fields were planted. Improved genetics and agronomics may further enhance energy sustainability and biofuel yield of switchgrass.

Comparison of dilute acid and ionic liquid pretreatment of switchgrass: Biomass recalcitrance, delignification and enzymatic saccharification

The efficiency of two biomass pretreatment technologies, dilute acid hydrolysis and dissolution in an ionic liquid, are compared in terms of delignification, saccharification efficiency and saccharide yields with switchgrass serving as a model bioenergy crop. When subject to ionic liquid pretreatment (dissolution and precipitation of cellulose by anti-solvent) switchgrass exhibited reduced cellulose crystallinity, increased surface area, and decreased lignin content compared to dilute acid pretreatment. Pretreated material was characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and chemistry methods. Ionic liquid pretreatment enabled a significant enhancement in the rate of enzyme hydrolysis of the cellulose component of switchgrass, with a rate increase of 16.7-fold, and a glucan yield of 96.0% obtained in 24h. These results indicate that ionic liquid pretreatment may offer unique advantages when compared to the dilute acid pretreatment process for switchgrass. However, the cost of the ionic liquid process must also be taken into consideration.

Visualization of biomass solubilization and cellulose regeneration during ionic liquid pretreatment of switchgrass

Auto‐fluorescent mapping of plant cell walls was used to visualize cellulose and lignin in pristine switchgrass (Panicum virgatum) stems to determine the mechanisms of biomass dissolution during ionic liquid pretreatment. The addition of ground switchgrass to the ionic liquid 1‐n‐ethyl‐3‐methylimidazolium acetate resulted in the disruption and solubilization of the plant cell wall at mild temperatures. Swelling of the plant cell wall, attributed to disruption of inter‐ and intramolecular hydrogen bonding between cellulose fibrils and lignin, followed by complete dissolution of biomass, was observed without using imaging techniques that require staining, embedding, and processing of biomass. Subsequent cellulose regeneration via the addition of an anti‐solvent, such as water, was observed in situ and provided direct evidence of significant rejection of lignin from the recovered polysaccharides. This observation was confirmed by chemical analysis of the regenerated cellulose. In comparison to untreated biomass, ionic liquid pretreated biomass produces cellulose that is efficiently hydrolyzed with commercial cellulase cocktail with high sugar yields over a relatively short time interval. Biotechnol. Bioeng. 2009; 104: 68–75 Published 2009 Wiley Periodicals, Inc.

Genetic modification of herbaceous plants for feed and fuel.

Referee: Dr. E. Charles Brummer, Forage Breeding and Genetics, 1204 Agromonomy, Iowa State University, Ames, IA 50011 Much of the research on the genetic modification of herbaceous plant cell walls has been conducted to improve the utilization of forages by ruminant livestock. The rumen of these animals is basically an anaerobic fermentation vat in which the micro flora break down the complex polysaccharides of plant cell walls into simpler compounds that can be further digested and absorbed by the mammalian digestive system. Research on improving the forage digestibility of switchgrass, Panicum virgatum L., and other herbaceous species has demonstrated that genetic improvements can be made in forage quality that can have significant economic value. To meet future energy needs, herbaceous biomass will need to be converted into a liquid fuel, probably ethanol, via conversion technologies still under development. If feedstock quality can be genetically improved, the economics and efficiency of the conversio...

Opportunities and roadblocks in utilizing forages and small grains for liquid fuels

This review focuses on the potential advantages and disadvantages of forages such as switchgrass (Panicum virgatum), and two small grains: sorghum (Sorghumbicolor), and wheat (Triticum aesitvum), as feedstocks for biofuels. It highlights the synergy provided by applying what is known from forage digestibility and wheat and sorghum starch properties studies to the biofuels sector. Opportunities therefore, exist to improve biofuel qualities in these crops via genetics and agronomics. In contrast to cereal crops, switchgrass still retains tremendous exploitable genetic diversity, and can be specifically improved to fit a particular agronomic, management, and conversion platform. Combined with emerging studies on switchgrass genomics, conversion properties and management, the future for genetic modification of this species through conventional and molecular breeding strategies appear to be bright. The presence of brown-midrib mutations in sorghum that alter cell wall composition by reducing lignin and other attributes indicate that sorghum could serve as an important model species for C4-grasses. Utilization of the brown-midrib traits could lead to the development of forage and sweet sorghums as novel biomass crops. Additionally, wheat crop residue, and wheat and sorghum with improved starch content and composition represent alternate biofuel sources. However, the use of wheat starch as a biofuel is unlikely but its value as a model to study starch properties on biofuel yields holds significant promise.

Genetic modification of lignin concentration affects fitness of perennial herbaceous plants

Abstract Populations of four perennial herbaceous species that were genetically modified for altered lignin content (or associated forage digestibility) by conventional plant breeding were evaluated for two agricultural fitness traits, plant survival and plant biomass, in three Northcentral USA environments for more than 4 years. Reduced lignin concentration or increased digestibility resulted in increased winter mortality in two of four species and reduced biomass in one species. Results from other experiment indicate that these apparent genetic correlations may be ephemeral, suggesting that selection for fitness can be successful within high-digestibility or low-lignin germplasm. Results indicate that perennial plants genetically engineered with altered lignin concentration or composition for use in livestock, pulp and paper, or bioenergy production should be evaluated for fitness in field environments prior to use in agriculture.

Plant species composition and biofuel yields of conservation grasslands

Marginal croplands, such as those in the Conservation Reserve Program (CRP), have been suggested as a source of biomass for biofuel production. However, little is known about the composition of plant species on these conservation grasslands or their potential for ethanol production. Our objective was to assess the potential of CRP and other conservation grasslands for biofuel production, describing the relationships of plant species richness and tall native C4 prairie grass abundance with plant chemical composition and the resulting potential ethanol yield. We determined plant species composition and diversity at multiple scales with the modified Whittaker plot technique, aboveground biomass, plant chemical composition, and potential ethanol yield at 34 sites across the major ecological regions of the northeastern USA. Conservation grasslands with higher numbers of plant species had lower biomass yields and a lower ethanol yield per unit biomass compared with sites with fewer species. Thus, biofuel yield per unit land area decreased by 77% as plant species richness increased from 3 to 12.8 species per m2. We found that, as tall native C4 prairie grass abundance increased from 1.7% to 81.6%, the number of plant species decreased and aboveground biomass per unit land area and ethanol yield per unit biomass increased resulting in a 500% increased biofuel yield per unit land area. Plant species richness and composition are key determinants of biomass and ethanol yields from conservation grasslands and have implications for low-input high-diversity systems. Designing systems to include a large proportion of species with undesirable fermentation characteristics could reduce ethanol yields.

In vitro gas production as a surrogate measure of the fermentability of cellulosic biomass to ethanol.

Current methods for measuring ethanol yields from lignocellulosic biomass are relatively slow and are not well geared for analyzing large numbers of samples generated by feedstock management and breeding research. The objective of this study was to determine if an in vitro ruminal fermentation assay used in forage quality research was predictive of results obtained using a conventional biomass-to-ethanol conversion assay. In the conventional assay, herbaceous biomass samples were converted to ethanol by Saccharomyces cerevisiae cultures in the presence of cellulase enzymes. Cultures were grown in sealed serum bottles and gas production monitored by measuring increasing head space pressure. Gas accumulation as calculated from the pressure measurements was highly correlated (r2>0.9) with ethanol production measured by gas chromatography at 24 h or 7 days. The same feedstocks were also analyzed by in vitro ruminal digestion, as also measured by gas accumulation. Good correlations (r2∼0.63–0.82) were observed between ethanol production during simultaneous saccharification and fermentation and gas accumulation in parallel in vitro ruminal fermentations. Because the in vitro ruminal fermentation assay can be performed without sterilization of the medium and does not require aseptic conditions, this assay may be useful for biomass feedstock agronomic and breeding research.

Field‐scale soil property changes under switchgrass managed for bioenergy

The capacity of perennial grasses to affect change in soil properties is well documented but information on switchgrass (Panicum virgatum L.) managed for bioenergy is limited. An on‐farm study (10 fields) in North Dakota, South Dakota, and Nebraska was sampled before switchgrass establishment and after 5 years to determine changes in soil bulk density (SBD), pH, soil phosphorus (P), and equivalent mass soil organic carbon (SOC). Changes in SBD were largely constrained to near‐surface depths (0–0.05 m). SBD increased (0–0.05 m) at the Nebraska locations (mean=0.16 Mg m−3), while most South Dakota and North Dakota locations showed declines in SBD (mean=−0.18 Mg m−3; range=−0.42–0.07 Mg m−3). Soil pH change was significant at five of the 10 locations at near surface depths (0–0.05 m), but absolute changes were modest (range=−0.67–0.44 pH units). Available P declined at all sites where it was measured (North Dakota and South Dakota locations). When summed across the surface 0.3 m depth, annual decreases in available P averaged 1.5 kg P ha−1 yr−1 (range=0.5–2.8 kg P ha−1 yr−1). Averaged across locations, equivalent mass SOC increased by 0.5 and 2.4 Mg C ha−1 yr−1 for the 2500 and 10 000 Mg ha−1 soil masses, respectively. Results from this study underscore the contribution of switchgrass to affect soil property changes, though considerable variation in soil properties exists within and across locations.

Analysis of expressed sequence tags and the identification of associated short tandem repeats in switchgrass.

Switchgrass is a large, North American, perennial grass that is being evaluated as a potential energy crop. Expressed sequence tags (ESTs) were generated from four switchgrass cv. “Kanlow” cDNA libraries to create a gene inventory of 7,810 unique gene clusters from a total of 11,990 individual sequences. Blast similarity searches to SwissProt and GenBank non-redundant protein and nucleotide databases were performed and a total of 79% of these unique clusters were found to be similar to existing protein or nucleotide sequences. Tentative functional classification of 61% of the sequences was possible by association with appropriate gene ontology descriptors. Significant differential representation between genes in leaf, stem, crown, and callus libraries was observed for many highly expressed genes The unique gene clusters were screened for the presence of short tandem repeats for further development as microsatellite markers. A total of 334 gene clusters contained repeats representing 3.8% of the ESTs queried.