Tense wood makes better biomass

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 characterize 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 a 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 percent cellulose,
whereas wood is normally composed of 40 to 55 percent 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.

“Recalcitrance
of plants is ultimately a reflection of a series of integrated plant
cell walls, components, structures and how they are put together,” said
co-author Arthur Ragauskas of Georgia Institute of Technology. “This
paper illustrates that you need to use a holistic, integrated approach
to study the totality of recalcitrance.”

Using the current study
as a model, the researchers are extending their investigation of tension
wood down to the molecular level and hope to eventually unearth the
genetic basis behind its desirable physical features. Although tension
wood itself is not considered to be a viable feedstock option, insight
gleaned from studying its unique physical and molecular characteristics
could be used to design and select more suitably tailored bioenergy
crops.