Research into the lignin in plant cells is determining a lot about the specific plants that can be used for cellulosic ethanol production in the future. Research with poplar trees shows lignin blocks extracting the sugars, but the research also is making progress for solutions in identifying specific poplar strains/varieties that more easily release sugars.

All of this research could be used to some extent with corn hybrids as corn stover becomes a cellulosic ethanol feedstock in the future. 

The Department of Energy's BioEnergy Science Center has already, though major cooperative efforts of several research teams, narrowed down a large collection of poplar tree candidates and identified winners for future use in biofuel production.

The research was published as "Lignin content in natural Populus variants affects sugar release," in the Proceedings of the National Academy of Sciences.

Lignin serves as a major roadblock for biofuel production because it forms strong bonds with sugars and interferes with access to these carbohydrates, making it difficult to extract the plant's sugars contained in cellulose and hemicellulose.

"The real driver for bioenergy is how to get sugar as cheaply as possible from these recalcitrant materials," said Charles Wyman of the Bourns College of Engineering's Center for Environmental Research and Technology at the University of California, Riverside, "We're looking for clues as to which traits in these poplar materials will lead to better sugar release."

The analysis has revealed a correlation between one plant trait, the S/G ratio, and increased sugar yields. The ratio refers to the two main building blocks of lignin – syringyl and guaiacyl subunits, the research scientists noted in the published report.

The team's research also pinpointed certain poplar samples that produced unusually high sugar yields with no pretreatment. Biofuel production typically requires various pretreatments, such as applying high temperature and pressure to the biomass. Reducing pretreatment would represent a substantial decrease in the price of ethanol produced from lignocellulosic feedstocks.

From this work, “superior poplar cultivars” may soon be available for commercial testing and propagation as part of the nation’s move forward to low-cost cellulosic ethanol production