Investigation of tension wood formation and 2,6-dichlorbenzonitrile application in short rotation coppice willow composition and enzymatic saccharification

Abstract

BackgroundShort rotation coppice willow is a potential lignocellulosic feedstock in the United Kingdom and elsewhere; however, research on optimising willow specifically for bioethanol production has started developing only recently. We have used the feedstock Salix viminalis × Salix schwerinii cultivar 'Olof' in a three-month pot experiment with the aim of modifying cell wall composition and structure within the stem to the benefit of bioethanol production. Trees were treated for 26 or 43 days with tension wood induction and/or with an application of the cellulose synthesis inhibitor 2,6-dichlorobenzonitrile that is specific to secondary cell walls. Reaction wood (tension and opposite wood) was isolated from material that had received the 43-day tension wood induction treatment.ResultsGlucan content, lignin content and enzymatically released glucose were assayed. All measured parameters were altered without loss of total stem biomass yield, indicating that enzymatic saccharification yield can be enhanced by both alterations to cell wall structure and alterations to absolute contents of either glucan or lignin.ConclusionsFinal glucose yields can be improved by the induction of tension wood without a detrimental impact on biomass yield. The increase in glucan accessibility to cell wall degrading enzymes could help contribute to reducing the energy and environmental impacts of the lignocellulosic bioethanol production process.

QTL Mapping of Wood FT-IR Chemotypes Shows Promise for Improving Biofuel Potential in Short Rotation Coppice Willow (Salix spp.)

“…The highly significant and positive correlations between FT-IR signals assigned to acetyl and Sor G-lignin, and between cellulose/hemicellulose/acetyl and lignin observed in this study (Table 3) are expected since they reflect the proportion of different cell wall layers in the willow stem biomass. The chemistry of this type of biomass was shown to be primarily affected by the content of tension wood in woody stems [55,56]. Low-tension wood individuals have high lignin and acetylated xylan contents, which are characteristic for the S-wall layers, while individuals with high proportion of tension wood have low lignin and acetylated xylan contents and high crystalline cellulose and galactan contents typically found in the G-layers [57].…”

Reaction wood – a key cause of variation in cell wall recalcitrance in willow

“…This unique cell wall layer differs from the normal fibre cell wall and is thought to be non-lignified and mainly composed of cellulose with the potential additions of arabinogalactan and xyloglucan [16-18]. Less is known regarding OW composition in angiosperms and only recently has it been shown to have the defining characteristic of increased lignin and cell wall recalcitrance when compared with normal wood [19,20]. …”

“…< 15% lignin on a mass basis) show reduced recalcitrance [27], none of the natural variation in basic cell wall compositional components (such as lignin and sugar contents) account sufficiently well for this variability in cell wall recalcitrance, leaving its fundamental causes unresolved. A number of studies have characterised the composition of the cell walls of RW (TW & OW) and normal wood (NW) as well as their response to pretreatment and/or enzymatic saccharification [19,23,28,29]. There is compelling evidence from this literature that ‘isolated’ TW has cell wall sugars that are more accessible to enzymatic saccharification when compared with NW and/or OW and, importantly, that RW induction can influence net cell wall recalcitrance over the ‘whole tree’ biomass.…”

“…The amount of G-fibres can be visualised using histology on single transverse sections of wood [21], but this gives little indication of their mass proportion over the whole length of the stem/tree. Also, the amount of OW, which recent phenotypic and transcriptomic work indicates is distinct from normal wood [19,30-32], cannot easily be distinguished based on histology. Because of the above, we have been careful in this work to focus our experimentation and interpretation on exploring the potential effects in terms of overall RW and to avoid unsupported linkages to TW formation.…”

Simultaneous pretreatment and saccharification: Green technology for enhanced sugar yields from biomass using a fungal consortium

“…However, few studies have investigated the optimization of saccharification process and the quality of short rotation coppice (SRC) willow (Salix koreensis) for this end use. Of the crop feed stocks 4 available, there is considerable potential for the SRC willow to be used as a dedicated bioenergy crop for lignocellulosic saccharification and biofuel production (Brereton et al, 2011). However, little work has been done to realistically meet the intended targets for future global demand.…”