Genetic Parameters of Factors Affecting the Biomass Recalcitrance of Douglas Fir Trees

Abstract

Although forestry residuals provide a potentially abundant source of biomass, Douglas fir is a particularly challenging feedstock to utilize in the biochemical conversion to fuels and value-added chemicals due to its high levels of biomass recalcitrance. A greater understanding of the underlying factors behind highly recalcitrant biomass is critical in overcoming this problem. Building on earlier efforts to establish a protocol and a “recalcitrance factor” for screening the recalcitrance of trees, this study attempts to provide the first look into the genetic factors behind recalcitrance in Douglas fir with the possibility of using selective breeding and tree improvement practices to reduce recalcitrance in future generations of our forest products. Samples from over 250 Douglas fir trees in a second-cycle progeny test were collected and subjected to screening. Samples were subjected to a dilute-acid pretreatment and a subsequent enzymatic hydrolysis procedure, ultimately measuring the raw wood density, pretreatment yield, the holocellulose content of pretreated samples, hydrolyzability, and recalcitrance factor. From these data, the heritability, genetic gains, and genetic correlations were estimated. Based on these results, we predict that modifying recalcitrance in tree improvement may be feasible, but would likely require some additional understanding and improved screening techniques.