DOI: 10.1126/science.1133306 , 1598 (2006); 314Science et al.David Tilman,High-Diversity Grassland BiomassCarbon-Negative Biofuels from Low-Input www.sciencemag.org (this information is current as of August 26, 2009 ):The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/314/5805/1598version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/314/5805/1598/DC1 can be found at: Supporting Online Materialfound at: can berelated to this articleA list of selected additional articles on the Science Web sites http://www.sciencemag.org/cgi/content/full/314/5805/1598#related-content http://www.sciencemag.org/cgi/content/full/314/5805/1598#otherarticles, 8 of which can be accessed for free: cites 23 articlesThis article 135 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/content/full/314/5805/1598#otherarticles 25 articles hosted by HighWire Press; see: cited byThis article has been http://www.sciencemag.org/cgi/collection/ecologyEcology : subject collectionsThis article appears in the following http://www.sciencemag.org/about/permissions.dtl in whole or in part can be found at: this articlepermission to reproduce of this article or about obtaining reprintsInformation about obtaining registered trademark of AAAS. is aScience2006 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on August 26, 2009 www.sciencemag.orgDownloaded from18. A. Trumpp et al., Nature 414, 768 (2001).19. M. N. Chamorro et al., EMBO J. 24, 73 (2005).20. E. H. Jho et al., Mol. Cell. Biol. 22, 1172 (2002).21. H. Lickert et al., Development 132, 2599 (2005).22. M. Morkel et al., Development 130, 6283 (2003).23. U. de Lichtenberg, L. J. Jensen, S. Brunak, P. Bork,Science 307, 724 (2005).24. We thank G. Glasko, J. Pace, and B. Brede for their help;R. Kopan, E. Furlong, J. Gerton, C. Seidel, B. Cheyette, andmembers of the Pourquié lab for comments; andS. Esteban for artwork. J.C. research supported by NSF grantDMS-0426148. This work was supported by Stowers Institutefor Medical Research and Defense Advanced ResearchProjects Agency (DARPA) grant 00001112 to O.P. O.P. is aHoward Hughes Medical Investigator.Supporting Online Materialwww.sciencemag.org/cgi/content/full/1133141/DC1Materials and MethodsFigs. S1 to S4Tables S1 to S5References28 July 2006; accepted 2 November 2006Published online 9 November 2006;10.1126/science.1133141Include this information when citing this paper.Carbon-Negative Biofuelsfrom Low-Input High-DiversityGrassland BiomassDavid Tilman,1* Jason Hill,1,2Clarence Lehman1Biofuels derived from low-input high-diversity (LIHD) mixtures of native grassland perennials canprovide more usable energy, greater greenhouse gas reductions, and less agrichemical pollution perhectare than can corn grain ethanol or soybean biodiesel. High-diversity grasslands had increasinglyhigher bioenergy yields that were 238% greater than monoculture yields after a decade. LIHDbiofuels are carbon negative because net ecosystem carbon dioxide sequestration (4.4 megagramhectare−1year−1of carbon dioxide in soil and roots) exceeds fossil carbon dioxide release duringbiofuel production (0.32 megagram hectare−1year−1). Moreover, LIHD biofuels can be produced onagriculturally degraded lands and thus need to neither displace food production nor cause loss ofbiodiversity via habitat destruction.Globally escalating demands for bothfood (1) and energy (2) have raisedconcerns about the potential for food-based biofuels to be sustainable, abundant, andenvironmentally beneficial energy sources. Cur-rent biofuel production competes for fertileland with food production, increases pollutionfrom fertilizers and pesticides, and threatensbiodiversity when natural lands are convertedto biofuel production. The two major classes ofbiomass for biofuel production recognized todate are monoculture crops grown on fertilesoils (such as corn, soybeans, oilseed rape,switchgrass, sugarcane, willow, and hybridpoplar) (3–6) and waste biomass (such as straw,corn stover, and waste wood) (7–9). Here, weshow the potential for a third major source ofbiofuel biomass, high-diversity mixtures ofplants grown with low inputs on agriculturallydegraded land, to address such concerns.We performed an experiment on agricul-turally degraded and abandoned nitrogen-poorsandy soil. We determined bioenergy produc-tion and ecosystem carbon sequestration in 152plots, planted in 1994, containing variouscombinations of 1, 2, 4, 8, or 16 perennialherbaceous grassland species (table S1) (10).Species composition of each plot was deter-mined by random draw from a pool of species.Plots were unfertilized, irrigated only duringestablishment, and otherwise grown with lowinputs (10). The 16-species plots are the high-est diversity, or the LIHD (low-input, high-diversity), treatment. All plots were burned inearly spring to remove aboveground biomassbefore growth began. Soil samples, collectedbefore planting in 1994 and again in 2004,determined carbon sequestration in soil. Plotswere sampled annually from 1996 to 2005 foraboveground biomass production.Annual production of aboveground bio-energy (i.e., biomass yield multiplied by energyreleased upon combustion) (10) was an ap-proximate log function of planted species num-ber (Fig. 1A). On average for the last 3 years ofthe experiment (2003–2005), 2-, 4-, 8-, and 16-species plots produced 84%, 100%, 157%, and238% more bioenergy, respectively, than didplots planted with single species. In a repeatedmeasures multivariate analysis of variance,annual bioenergy production was positivelydependent on the number of planted species(F1, 155=68.4,P <0.0001),ontime(F9, 147=8.81, P < 0.0001), and on a positive time-by-species number interaction (F9, 147=11.3,P <0.0001). The interaction occurred becausebioenergy production increased more throughtime in LIHD treatments than in monoculturesand low-diversity treatments, as shown by theratio of bioenergy in LIHD (16 species) plots tothose in 8-, 4-, 2-, and 1-species plots (Fig. 1B).The gross bi oenergy yield from L