Tension wood structure and morphology conducive for better enzymatic digestion

Abstract

BackgroundTension wood is a type of reaction wood in response to bending or leaning stem as a corrective growth process. Tension wood is formed by both natural and man-made processes. Most attractively, tension wood contains higher glucan content and undergoes higher enzymatic conversion to fermentable sugars. Here, we have employed structural techniques, small-angle neutron scattering (SANS) and wide-angle X-ray diffraction (WAXD) to elucidate structural and morphological aspects of tension wood conducive to higher sugar yields.ResultsSmall-angle neutron scattering data exhibited a tri-modal distribution of the fibril cross-sectional dimension. The smallest size, 22 Å observed in all samples concurred with the WAXD results of the control and opposite side samples. This smallest and the most abundant occurring size was interpreted as the cellulose elementary microfibril diameter. The intermediate size of 45 Å, which is most pronounced in the tension side sample and consistent with WAXD results for tension side sample, indicates association of neighboring elementary microfibrils to form larger crystallite bundles. The largest size 61 Å observed by SANS was however not observed by WAXD and therefore associated to mesopores.ConclusionsStructure and morphology of tension wood is different from control wood. Cellulose crystallinity increases, lignin content is lower and the appearance of mesopores with 61 Å diameter is observed. Despite the presence of higher crystalline cellulose content in tension side, the lower lignin content and may be combined with the abundance of mesopores, substantially improves enzyme accessibility leading to higher yields in cellulose digestion.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1043-x) contains supplementary material, which is available to authorized users.

Moisture-related changes in the nanostructure of woods studied with X-ray and neutron scattering

“…1) was required to model the scattering on the q range from 0:01 to 0:1Å À1 (Table S2 and Figure S5). The peculiar shape of the SANS intensity curve of beech tension wood is similar to those reported for poplar tension wood by Sawada et al (2018), who assigned the additional contribution to associated CMFs and mesopores (diameter 6 nm), and it is therefore suggested to be characteristic of tension wood samples. The SANS results showed small but rather consistent differences between never-dried and dried/rewetted structures of the samples (Table 2).…”

“…However, the numerical values of a and L 200 were significantly larger in the tension wood samples than in any of the other samples. These results are in line with a longitudinally alternating structure for CMF bundles in the G-layer of tension wood, with pores of approximately 6 nm in diameter occasionally separating the fibrils (Clair et al 2008;Sawada et al 2018). Such diversity in the structure might also explain the seeming discrepancies between the data obtained for the tension wood samples in this study.…”

“…8) and SANS (2 R in Table 2) results for beech tension wood. Unlike in the softwood samples, however, these changes could probably be more reliably assigned to the coalescence of the CMFs, which is presumably common in the G-layer (Sawada et al 2018).…”

Ultrastructural X-ray scattering studies of tropical and temperate hardwoods used as tonewoods

“…It has been detected in several previous X-ray diffraction studies, that the cellulose crystallite width in TW is similar to that observed in this study i.e. around 4-5 nm (Müller et al 2006;Ruelle et al 2007;Leppänen et al 2011;Sawada et al 2018). The more marked aggregation of cellulose crystallites has been suggested as an explanation for the larger widths in previous studies (Müller et al 2006;Sawada et al 2018), and the lower lignin content of TW has been considered as one of the factors behind this (Foston et al 2011).…”

“…around 4-5 nm (Müller et al 2006;Ruelle et al 2007;Leppänen et al 2011;Sawada et al 2018). The more marked aggregation of cellulose crystallites has been suggested as an explanation for the larger widths in previous studies (Müller et al 2006;Sawada et al 2018), and the lower lignin content of TW has been considered as one of the factors behind this (Foston et al 2011). It can also be noted that based on specific gravity all these samples represent class 3 tonewoods (see Table 1), i.e.…”