Bioenergy from trees

Determinants of Shoot Biomass Production in Mulberry: Combined Selection with Leaf Morphological and Physiological Traits

Physiological and morphological traits have a considerable impact on the biomass production of fast-growing trees. To compare cultivar difference in shoot biomass and investigate its relationships with leaf functional traits in mulberry, agronomic traits and 20 physiological and morphological attributes of 3-year-old mulberry trees from eight cultivars growing in a common garden were analyzed. The cultivars Xiang7920, Yu711, and Yunsang2 had higher shoot fresh biomass (SFB), which was closely associated with their rapid leaf expansion rate, large leaf area, and high stable carbon isotope composition (δ¹³C). Conversely, the cultivars 7307, Husang32, Wupu, Yunguo1, and Liaolu11 were less productive, and this was primarily the result of slower leaf expansion and smaller leaf size. Growth performance was negatively correlated with leaf δ¹³C and positively correlated with the total nitrogen concentration, indicating that a compromise exists in mulberry between water use efficiency (WUE) (low δ¹³C) and high nitrogen consumption for rapid growth. Several morphological traits, including the maximum leaf area (LA_max), leaf width and length, petiole width and length, leaf number per shoot, and final shoot height were correlated with SFB. The physiological traits that were also influential factors of shoot biomass were the leaf δ¹³C, the total nitrogen concentration, and the water content. Among the studied leaf traits, LA_max, leaf δ¹³C, and concentrations of chlorophyll a and b were identified as the most representative predictor variables for SFB, accounting for 73% of the variability in SFB. In conclusion, a combination of LA_max, leaf δ¹³C, and chlorophyll should be considered in selection programs for high-yield mulberry cultivars.

Biotechnology for bioenergy dedicated trees: meeting future energy demands

With the increase in human demands for energy, purpose-grown woody crops could be part of the global renewable energy solution, especially in geographical regions where plantation forestry is feasible and economically important. In addition, efficient utilization of woody feedstocks would engage in mitigating greenhouse gas emissions, decreasing the challenge of food and energy security, and resolving the conflict between land use for food or biofuel production. This review compiles existing knowledge on biotechnological and genomics-aided improvements of biomass performance of purpose-grown poplar, willow, eucalyptus and pine species, and their relative hybrids, for efficient and sustainable bioenergy applications. This includes advancements in tree in vitro regeneration, and stable expression or modification of selected genes encoding desirable traits, which enhanced growth and yield, wood properties, site adaptability, and biotic and abiotic stress tolerance. Genetic modifications used to alter lignin/cellulose/hemicelluloses ratio and lignin composition, towards effective lignocellulosic feedstock conversion into cellulosic ethanol, are also examined. Biotech-trees still need to pass challengeable regulatory authorities’ processes, including biosafety and risk assessment analyses prior to their commercialization release. Hence, strategies developed to contain transgenes, or to mitigate potential transgene flow risks, are discussed.

Chemical composition, pretreatments and saccharification of Senna siamea (Lam.) H.S. Irwin & Barneby: An efficient biomass producing tree legume

Protocols were developed for efficient release of glucose from the biomass of Senna siamea, one of the highly efficient biomass producing tree legumes. Composition of mature, 1year and 2years coppice biomass were analysed. For the hydrolysis of the glucan, two pretreatments, cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) and alkali (sodium hydroxide) were used; COSLIF (85% phosphoric acid, 45min incubation at 50°C) pretreated mature biomass exhibited best result in which 88.90% glucose released after 72h of incubation with the use of 5 filter paper units (FPU) of cellulase and 10 international units (IU) of β-glucosidase per gram of glucan. Of the biomass of different particle sizes (40-200mesh) used for saccharification, 40-60mesh shown the maximum glucose release. COSLIF pretreated mature, 1year and 2years coppice biomass showed equivalent glucose release profiles.

Transcriptome analysis of xylose metabolism in the thermotolerant methylotrophic yeast Hansenula polymorpha

The thermotolerant methylotrophic yeast Hansenula polymorpha is able to grow at elevated temperature up to 48 °C as one of a few yeast strains which are naturally capable of alcoholic fermentation of xylose, a pentose sugar abundant in lignocellulosic biomass. However, the current level of ethanol production from xylose by H. polymorpha is still very low compared to those of other xylose-fermenting strains. Therefore, it is necessary to analyze and remodel the xylose metabolism in H. polymorpha at the whole genome level to identify and overcome these limits. In the present study, the transcriptomes of H. polymorpha grown on xylose were compared with those of glucose-grown cells under both aerobic and microaerobic conditions. Approximately, two percent of H. polymorpha genes were either up- or down-regulated by more than two-fold during the growth on xylose. The majority of the up-regulated genes were involved in metabolism. Some genes involved in xylose metabolism, such as XYL1, XYL2, and TAL1 were also up-regulated, despite the fact that the differences in their induction level were only about three-fold. On the other hand, the majority of the down-regulated genes were involved in metabolism and cellular transport. Interestingly, some genes involved in glycolysis and ethanol fermentation were also repressed during growth on xylose, suggesting that these genes are good targets for engineering H. polymorpha to improve xylose fermentation.