First-of-a-kind tension wood study broadens biofuels research

Taking a cue from Mother Nature, researchers at the Department of Energy's BioEnergy Science Center have undertaken a first-of-its-kind study of a naturally occurring phenomenon in trees to spur the development of more efficient bioenergy crops.

Tension wood, which forms naturally in hardwood trees in response to bending stress, is known to possess unique features that render it desirable as a bioenergy feedstock. Although individual elements of tension wood have been studied previously, the BESC team is the first to use a comprehensive suite of techniques to systematically characterise tension wood and link the wood's properties to sugar release.
 
Plant sugars, known as cellulose, are fermented into alcohol for use as biofuel.

"There has been no integrated study of tension stress response that relates the molecular and biochemical properties of the wood to the amount of sugar that is released," said Oak Ridge National Laboratory's Udaya Kalluri, a co-author on the study.

The work, published in Energy & Environmental Science, describes tension wood properties including an increased number of woody cells, thicker cell walls, more crystalline forms of cellulose and lower lignin levels, all of which are desired in an biofuel crop.

"Tension wood in poplar trees has a special type of cell wall that is of interest because it is composed of more than 90 per cent cellulose, whereas wood is normally composed of 40 to 55 per cent cellulose," Kalluri said. "If you increase the cellulose in your feedstock material, then you can potentially extract more sugars as the quality of the wood has changed. Our study confirms this phenomenon."

The study's cohesive approach also provides a new perspective on the natural plant barriers that prevent the release of sugars necessary for biofuel production, a trait scientists term as recalcitrance.