Probing the Natural Variation in Poplar Trees to Increase the Yield of Sugars for Biofuels
A promising source of renewable “next generation” fuels is from the lignocellulosic biomass of poplar trees, from which sugars can be extracted and fermented to produce biofuels. These sugars, in the form of cellulose and hemicellulose, are embedded within lignin, a complex polymer composed of varying ratios of phenylpropanoid subunits. The rigid structure of lignin is a critical component of the plant cell wall, but this same trait impedes extraction of the sugars. Researchers at the DOE BioEnergy Research Center (BESC) at Oak Ridge National Laboratory measured lignin content and composition in a large (1100 individual) sample of undomesticated poplar trees and found that variation between individuals was large and significant. Using a high-throughput screening method, samples were tested for total sugar release with or without various pretreatments. The total amounts of sugars released varied widely among samples, and, as expected, a strong negative correlation between sugar release and lignin content was observed. However, the large data set allowed the researchers to discover critical exceptions to the overall correlation. The negative correlation did not apply to trees with a certain composition of lignin, and, for some trees with typical lignin content and composition, a very high volume of sugars were released. These results indicate that although recalcitrance to sugar release is partly determined by lignin content, lignin composition and other factors are also critical, and underscores the need for further research on cell wall structure in order to rationally design high-yielding bioenergy feedstocks for large-scale industrial use. The research has just been published in the Proceedings of the National Academy of Sciences (USA).
Studer, M.H., M.F. Davis, R.W. Sykes, B.H. Davison, M. Keller , G.A. Tuskan, and C.E. Wyman. 2011. Lignin Content in Natural Populus Variants Affects Sugar Release.” PNAS doi:10.1073/pnas.1009252108.