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GLBRC's Publications

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Publications

When it comes to interdisciplinary collaboration, the titles of GLBRC publications speak for themselves. Each new year of operation has seen more publications from multiple labs that span the four Research Areas, accelerating the Center's production of the basic research that generates technology to convert cellulosic biomass to advanced biofuels.

Publications

Cell-wall carbohydrates and their modification as a resource for biofuels

Markus Pauly; Kenneth Keegstra

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2008

Plant cell walls represent the most abundant renewable resource on this planet. Despite their great abundance, only 2% of this resource is currently used by humans. Hence, research into the feasibility of using plant cell walls in the production of cost-effective biofuels is desirable. The main bottleneck for using wall materials is the recalcitrance of walls to efficient degradation into fermentable sugars. Manipulation of the wall polysaccharide biosynthetic machinery or addition of wall structure-altering agents should make it possible to tailor wall composition and architecture to enhance sugar yields upon wall digestion for biofuel fermentation. Study of the biosynthetic machinery and its regulation is still in its infancy and represents a major scientific and technical research challenge. Of course, any change in wall structure to accommodate cost-efficient biofuel production may have detrimental effects on plant growth and development due to the diverse roles of walls in the life of a plant. However, the diversity and abundance of wall structures present in the plant kingdom gives hope that this challenge can be met.

Disrupting two Arabidopsis thaliana xylosyltransferase genes results in plants deficient in xyloglucan, a major primary cell wall component

David M. Cavalier; Oliver Lerouxel; Lutz Neumetzler; Kazuchika Yamauchi; Antje Reinecke; Glenn Freshour; Alga Zabotina; Michael G. Hahn; Ingo Burgert; Markus Pauly; Natasha V. Raikhel; Kenneth Keegstra

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2008

Xyloglucans are the main hemicellulosic polysaccharides found in the primary cell walls of dicots and nongraminaceous monocots, where they are thought to interact with cellulose to form a three-dimensional network that functions as the principal load-bearing structure of the primary cell wall. To determine whether two Arabidopsis thaliana genes that encode xylosyltransferases, XXT1 and XXT2, are involved in xyloglucan biosynthesis in vivo and to determine how the plant cell wall is affected by the lack of expression of XXT1, XXT2, or both, we isolated and characterized xxt1 and xxt2 single and xxt1 xxt2 double T-DNA insertion mutants. Although the xxt1 and xxt2 mutants did not have a gross morphological phenotype, they did have a slight decrease in xyloglucan content and showed slightly altered distribution patterns for xyloglucan epitopes. More interestingly, the xxt1 xxt2 double mutant had aberrant root hairs and lacked detectable xyloglucan. The reduction of xyloglucan in the xxt2 mutant and the lack of detectable xyloglucan in the xxt1 xxt2 double mutant resulted in significant changes in the mechanical properties of these plants. We conclude that XXT1 and XXT2 encode xylosyltransferases that are required for xyloglucan biosynthesis. Moreover, the lack of detectable xyloglucan in the xxt1 xxt2 double mutant challenges conventional models of the plant primary cell wall.

Harnessing plant biomass for biofuels and biomaterials

Christoph Benning; Eran Pichersky

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2008

Modern societies have relied for more than a century on fossil carbon sources for the production of fuels or chemicals ranging from plastic polymers to drugs to food additives. The consequences of this utilization of fossil carbon-derived fuels – the release of carbon dioxide into the atmosphere – are no longer deniable. There is general agreement among leading scientists that the increased concentration of carbon dioxide in the atmosphere has contributed to the all-too-apparent global-warming trend. It is also clear that the increasingly high demand for fossil carbon will eventually deplete the existing stocks, with consequences not only in the area of energy but also in the wider chemical industry. Concerned citizens from scientists to policy makers have recognized the need for a reliable, renewable and affordable source of carbon in its chemically reduced form that can sustain future economic developments without having a negative impact on the environment. Discussion of solutions to overcome the current dependence on fossil carbon is conducted at all levels of society. The conversion of light energy into chemical energy by plant photosynthesis ranks prominently among the natural processes that can potentially meet the challenge. Plant biologists and biochemists are therefore at the forefront of developing schemes and ideas for an emerging bioeconomy that sustainably harnesses plant biomass.

Impacts of ethanol on planted acreage in market equilibrium

Hongli Feng; Bruce A. Babcock

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2008

Land use impacts of biofuel expansion have attracted a tremendous amount of attention because of the implications for the climate, the environment, and the food supply. To examine these impacts, we set up an economic framework that links input use and land allocation decisions with ethanol and agricultural commodity markets. Crops can be substitutes or complements in supply depending on the relative magnitude of three effects of crop prices: total cropland effect, land share effect, and input use effect. We show that with unregulated free markets, total cropland area increases with corn prices whether crops are substitutes or complements in supply. Similarly, higher corn yields from exogenous technical changes lead to cropland expansion. The impacts of yield increases for other crops are ambiguous. With a quantity mandate for ethanol, higher mandates mean larger cropland area if corn and other crops are substitutes in demand. For a given mandate, yield improvement causes total cropland to expand if crop demand is elastic enough, or to contract under a very general condition if crop demand is sufficiently inelastic.

Impacts of ethanol on planted acreage in market equilibrium (Iowa State Report)

Hongli Feng; Bruce A. Babcock

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2008

Land use impacts of biofuel expansion have attracted a tremendous amount of attention because of the implications for the climate, the environment, and the food supply. To examine these impacts, we set up an economic framework that links input use and land allocation decisions with ethanol and agricultural commodity markets. Crops can be substitutes or complements in supply depending on the relative magnitude of three effects of crop prices: total cropland effect, land share effect, and input use effect. We show that with unregulated free markets, total cropland area increases with corn prices whether crops are substitutes or complements in supply. Similarly, higher corn yields from exogenous technical changes lead to cropland expansion. The impacts of yield increases for other crops are ambiguous. With a quantity mandate for ethanol, higher mandates mean larger cropland area if corn and other crops are substitutes in demand. For a given mandate, yield improvement causes total cropland to expand if crop demand is elastic enough, or to contract under a very general condition if crop demand is sufficiently inelastic.

Increasing corn for biofuel production reduces biocontrol services in agricultural landscapes

Douglas A. Landis; Mary M. Gardiner; Wopke van der Werf; Scott M. Swinton

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2008

Increased demand for corn grain as an ethanol feedstock is altering U.S. agricultural landscapes and the ecosystem services they provide. From 2006 to 2007, corn acreage increased 19% nationally, resulting in reduced crop diversity in many areas. Biological control of insects is an ecosystem service that is strongly influenced by local landscape structure. Here, we estimate the value of natural biological control of the soybean aphid, a major pest in agricultural landscapes, and the economic impacts of reduced biocontrol caused by increased corn production in 4 U.S. states (Iowa, Michigan, Minnesota, and Wisconsin). For producers who use an integrated pest management strategy including insecticides as needed, natural suppression of soybean aphid in soybean is worth an average of $33 ha(-1). At 2007-2008 prices these services are worth at least $239 million y(-1) in these 4 states. Recent biofuel-driven growth in corn planting results in lower landscape diversity, altering the supply of aphid natural enemies to soybean fields and reducing biocontrol services by 24%. This loss of biocontrol services cost soybean producers in these states an estimated $58 million y(-1) in reduced yield and increased pesticide use. For producers who rely solely on biological control, the value of lost services is much greater. These findings from a single pest in 1 crop suggest that the value of biocontrol services to the U.S. economy may be underestimated. Furthermore, we suggest that development of cellulosic ethanol production processes that use a variety of feedstocks could foster increased diversity in agricultural landscapes and enhance arthropod-mediated ecosystem services.

Microbes in the energy grid

James Tiedje; Timothy Donohue

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2008

The current surge in food and fuel prices has sounded an alarm showing why providing a sustainable global energy supply and minimizing climate change are arguably two of the greatest challenges facing 21st-century society. With adequate research and proper implementation, the diverse and often unseen inhabitants of the microbial world--bacteria, yeasts, fungi, and archaea--can help address these challenges.

Physiology and metabolism "Tear down this wall"

Markus Pauly; Kenneth Keegstra

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2008

Plant cell walls represent the most abundant renewable resource on this planet, with an estimated annual net primary production of land plants alone of 150–170 billion tons. Owing to their abundance, plant cell walls may play a key role in partially replacing fossil fuels by renewable source liquid fuels for transportation. Such strategies are part of the efforts to reduce greenhouse gas emissions caused by burning of fossil fuels. The major bottleneck in utilizing plant cell wall materials, often referred to as lignocellulosic biomass, for these purposes is their recalcitrance to efficient and cost-effective degradation to release fermentable sugars in high yield. In this issue of Current Opinion in Plant Biology, our aim is to give readers an up-to-date status report on the various wall structures found in plants, their biosynthesis and metabolism, and the differences between plant species, including potential energy crops such as grasses and trees. In addition, we have invited articles from our colleagues who work with fungi to enlighten us on the current prospects of using fungal enzymes to degrade wall polymers.

Plant triacylglycerols as feedstocks for the production of biofuels

Timothy P. Durrett; Christoph Benning; John B. Ohlrogge

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2008

Triacylglycerols produced by plants are one of the most energy-rich and abundant forms of reduced carbon available from nature. Given their chemical similarities, plant oils represent a logical substitute for conventional diesel, a non-renewable energy source. However, as plant oils are too viscous for use in modern diesel engines, they are converted to fatty acid esters. The resulting fuel is commonly referred to as biodiesel, and offers many advantages over conventional diesel. Chief among these is that biodiesel is derived from renewable sources. In addition, the production and subsequent consumption of biodiesel results in less greenhouse gas emission compared to conventional diesel. However, the widespread adoption of biodiesel faces a number of challenges. The biggest of these is a limited supply of biodiesel feedstocks. Thus, plant oil production needs to be greatly increased for biodiesel to replace a major proportion of the current and future fuel needs of the world. An increased understanding of how plants synthesize fatty acids and triacylglycerols will ultimately allow the development of novel energy crops. For example, knowledge of the regulation of oil synthesis has suggested ways to produce triacylglycerols in abundant non-seed tissues. Additionally, biodiesel has poor cold-temperature performance and low oxidative stability. Improving the fuel characteristics of biodiesel can be achieved by altering the fatty acid composition. In this regard, the generation of transgenic soybean lines with high oleic acid content represents one way in which plant biotechnology has already contributed to the improvement of biodiesel.

Preferential sequestration of microbial carbon in subsoils of a glacial-landscape toposequence, Dane County, WI, USA

Chao Liang; Teri C. Balser

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2008

Microorganisms participate in soil carbon storage by contributing biomass in the form of refractory microbial cell components. However, despite the important contribution of microbial biomass residues to the stable carbon pool, little is known about how the contribution of these residues to soil carbon storage varies as a function of depth. In this study, we evaluated microbial residue biomarkers (amino sugars) in varied pedogenic horizons from six soil profiles of two geographic sites on a glacial-landscape toposequence in Dane County, WI. We found that the amino sugars appeared to preferentially accumulate in subsoil. Specifically, although total amounts of amino sugars decreased downward through the profile as even as total organic carbon did, the rate of decrease was significantly lower, suggesting that these compounds are more refractory than general soil organic carbon. The proportion of amino sugars to soil organic carbon increased along the depth gradient (from top to bottom). with the exception of Bg horizons associated with high water tables. We also observed that microbial residue patterns measured by amino sugar ratio (e.g., glucosamine to muramic acid) showed different dynamic tendencies in the two different geographic sites, suggesting that residue carbon contribution by fungi and bacteria is likely site-specific and complex. In summary, regardless of the redox microenvironment created by groundwater dynamics in a given soil, our study supports the hypothesis that microbial residues are refractory and that they contribute to terrestrial carbon sequestration. (C) 2008 Elsevier B.V. All rights reserved.

Sustainable biofuels redux

Philip Robertson; Virginia H. Dale; Otto C. Doering; Steven P. Hamburg; Jerry M. Melillo; Michele M. Wander; William J. Parton; Paul R. Adler; Jacob N. Barney; Richard M. Cruse; Clifford S. Duke; Philip M. Fearnside; Ronald F. Follett; Holly K. Gibbs; Jose Goldemberg; David J. Mladenoff; Dennis Ojima; Michael W. Palmer; Andrew Sharpley; Linda Wallace; Kathleen C. Weathers; John A. Wiens; Wallace W. Wilhelm

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2008

Last May's passage of the 2008 Farm Bill raises the stakes for biofuel sustainability: A substantial subsidy for the production of cellulosic ethanol starts the United States again down a path with uncertain environmental consequences. This time, however, the subsidy is for both the refiners ($1.01 per gallon) and the growers ($45 per ton of biomass), which will rapidly accelerate adoption and place hard-to-manage pressures on efforts to design and implement sustainable production practices—as will a 2007 legislative mandate for 16 billion gallons of cellulosic ethanol per year by 2022. Similar directives elsewhere, e.g., the European Union's mandate that 10% of all transport fuel in Europe be from renewable sources by 2020, make this a global issue. The European Union's current reconsideration of this target places even more emphasis on cellulosic feedstocks (1). The need for knowledge- and science-based policy is urgent. Biofuel sustainability has environmental, economic, and social facets that all interconnect. Tradeoffs among them vary widely by types of fuels and where they are grown and, thus, need to be explicitly considered by using a framework that allows the outcomes of alternative systems to be consistently evaluated and compared. A cellulosic biofuels industry could have many positive social and environmental attributes, but it could also suffer from many of the sustainability issues that hobble grain-based biofuels, if not implemented the right way.

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