Pyrolysis of centimeter-scale wood particles is of practical interest and provides a sensitive test of pyrolysis models, especially their thermochemistry. In this paper we present an updated comprehensive pyrolysis model including chemical reactions and transport of heat and species, implemented independently in two different software environments. Results of the model are compared to experimental results of three independent sets of centimeter-scale experiments. Temperatures, mass losses, and rate of production of several gaseous and light tar species are included in the comparisons. Predictions and experiments agree qualitatively and in most cases have reasonable quantitative agreement. We also report comparisons of model predictions to literature data obtained in other regimes (thermogravimetric analysis and omogeneous tar cracking) in order to demonstrate that predictive capabilities of the model have not been compromised by the modifications presented here

SUMMARYThe phenylpropanoid biosynthetic pathway that generates lignin subunits represents a significant target for altering the abundance and composition of lignin. The global regulators of phenylpropanoid metabolism may include MYB transcription factors, whose expression levels have been correlated with changes in secondary cell wall composition and the levels of several other aromatic compounds, including anthocyanins and flavonoids. While transcription factors correlated with downregulation of the phenylpropanoid biosynthesis pathway have been identified in several grass species, few transcription factors linked to activation of this pathway have been identified in C4 grasses, some of which are being developed as dedicated bioenergy feedstocks. In this study we investigated the role of SbMyb60 in lignin biosynthesis in sorghum (Sorghum bicolor), which is a drought-tolerant, high-yielding biomass crop. Ectopic expression of this transcription factor in sorghum was associated with higher expression levels of genes involved in monolignol biosynthesis, and led to higher abundances of syringyl lignin, significant compositional changes to the lignin polymer and increased lignin concentration in biomass. Moreover, transgenic plants constitutively overexpressing SbMyb60 also displayed ectopic lignification in leaf midribs and elevated concentrations of soluble phenolic compounds in biomass. Results indicate that overexpression of SbMyb60 is associated with activation of monolignol biosynthesis in sorghum. SbMyb60 represents a target for modification of plant cell wall composition, with the potential to improve biomass for renewable uses.

Shrub willow has great potential as a dedicated bioenergy crop, but commercialization and adoption by growers and end-users will depend upon the identification and selection of high-yielding cultivars with biomass chemistry and quality amenable to conversion to biofuels and bioenergy. In this study, critical traits for biomass production were evaluated among new genotypes of shrub willow produced through hybrid breeding. This study assessed the variation in yield, pest and disease resistance, biomass composition, and wood density in shrub willow, as well as the impact of genotypic and environmental factors on these particular phenotypes. Analysis of clonal genotypes established on two contrasting sites in New York State, Tully and Belleville, showed statistical differences by site for all of the traits. The greatest yield was observed at Belleville, NY, for two cultivars, 'Fish Creek' (41 Mgha −1 ) and 'Onondaga' (40 Mgha −1 ). Yields of Salix eriocephala genotypes were lowest, and they displayed susceptibility to rust and beetle damage. Variation in cellulose content in the stem biomass was controlled by environmental factors, with the majority of the genotypes displaying greater cellulose content at Belleville compared with Tully. In contrast, wood density was significantly greater at Tully than Belleville, and cellulose content was correlated with wood density. There were no significant correlations between biomass yield and density or any of the composition traits. These trials demonstrate that new genotypes produce improved yield and pest and disease resistance, with diverse compositional traits that can be matched with conversion technologies.

Rapid determination of biomass composition is critical for the selection of shrub willow varieties with optimized biomass properties for conversion into fuels or chemicals. In order to improve the process for identifying and selecting shrub willow clones with distinct biomass composition, high-resolution thermogravimetric analysis (HR-TGA) was developed as a rapid, low-cost method for analyzing large numbers of willow biomass samples. In order to validate the HR-TGA method, bulk biomass collected from 2-year-old stems of a selected set of 25 shrub willow clones was analyzed using traditional wet chemistry techniques in addition to HR-TGA. The results of the wet chemistry and the HR-TGA method were compared using regression analysis resulting in R-squared values above 0.7 for the three main wood components, cellulose, hemicellulose, and lignin. Bark was removed from duplicate stem samples of the same clones, the proportion of bark was determined, and the debarked wood was used for HR-TGA analysis of composition. While there were significant differences in the proportions of lignin and cellulose in debarked wood compared to bulk biomass, as well as significant differences in bark percentage among clones, there was no correlation between bark percentage and bulk biomass component analysis. This work validates the effectiveness, precision, and accuracy of HR-TGA as a reasonably high-throughput method for biomass composition analysis and selection of shrub willow bioenergy crop varieties.

BackgroundGenetic improvement of shrub willow (Salix), a perennial energy crop common to temperate climates, has led to the development of new cultivars with improved biomass yield, pest and disease resistance, and biomass composition suitable for bioenergy applications. These improvements have largely been associated with species hybridization, yet little is known about the genetic mechanisms responsible for improved yield and performance of certain willow species hybrids.ResultsThe top performing genotypes in this study, representing advanced pedigrees compared with those in previous studies, were mostly triploid in nature and outperformed current commercial cultivars. Of the genotypes studied, the diploids had the lowest mean yield of 8.29 oven dry Mg ha−1 yr−1, while triploids yielded 12.65 Mg ha−1 yr−1, with the top five producing over 16 Mg ha−1 yr−1. Triploids had high stem area and height across all three years of growth in addition to greatest specific gravity. The lowest specific gravity was observed among the tetraploid genotypes. Height was the early trait most correlated with and the best predictor of third-year yield.ConclusionsThese results establish a paradigm for future breeding and improvement of Salix bioenergy crops based on the development of triploid species hybrids. Stem height and total stem area are effective traits for early prediction of relative yield performance.

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Polyploidy is a common observation in the genus Salix, including some of the shrub willow species currently being bred as a potential bioenergy feedstock. Breeding of shrub willow has produced new species hybrids, among which a disproportionate number of high-yielding genotypes are triploid, produced from crosses between diploid and tetraploid parents. These novel hybrids display significant variation in biomass compositional quality, including differences according to ploidy. The triploid and tetraploid genotypes possess lower lignin content than diploid genotypes. Biomass composition was also significantly different across the 3-year growth cycle typical of bioenergy plantings. There were differences in syringyl/guaiacyl (S:G) lignin ratios among the 75 genotypes examined, in addition to significant correlations with willow growth traits, yield, and composition. These differences suggest that a long-term strategy of breeding for triploid progeny will generate cultivars with improved growth traits and wood composition for conversion to biofuels.

Development of dedicated bioenergy crop production systems will require accurate yield estimates, which will be important for determining many of the associated environmental and economic impacts of their production. Shrub willow (Salix spp) is being promoted in areas of the USA and Canada due to its adaption to cool climates and wide genetic diversity available for breeding improvement. Willow breeding in North America is in an early stage, and selection of elite genotypes for commercialization will require testing across broad geographic regions to gain an understanding of how shrub willow interacts with the environment. We analyzed a dataset of first-rotation shrub willow yields of 16 genotypes across 10 trial environments in the USA and Canada for genotype-byenvironment interactions using the additive main effects and multiplicative interactions (AMMI) model. Mean genotype yields ranged from 5.22 to 8.58 oven-dry Mg ha À1 yr À1. Analysis of the main effect of genotype showed that one round of breeding improved yields by as much as 20% over check cultivars and that triploid hybrids, most notably Salix viminalis 9 S. miyabeana, exhibited superior yields. We also found important variability in genotypic response to environments, which suggests specific adaptability could be exploited among 16 genotypes for yield gains. Strong positive correlations were found between environment main effects and AMMI parameters and growing environment temperatures. These findings demonstrate yield improvements are possible in one generation and will be important for developing cultivar recommendations and for future breeding efforts.