In situ observation of shrinking and swelling of normal and compression Chinese fir wood at the tissue, cell and cell wall level

The shrinking and swelling of wood due to moisture changes are intrinsic material properties that control and limit the use of wood in many applications. Herein, hygroscopic deformations of normal and compression wood of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) were measured during desorption and absorption processes. The dimensional changes were observed in situ by an environmental scanning electron microscope and analyzed at different hierarchical levels (tissue, cell and cell wall). The relationship between moisture variation and hygroscopic deformation was measured. During initial desorption periods from 95 to 90 or 75% RH, an expansion of the lumen and a shrinkage of the cell wall were observed, revealing a non-uniform and directional deformation of single wood cells. The variation of shrinking or swelling at different hierarchical levels (tissue, cell and cell wall) indicates that the hygroscopic middle lamella plays a role in the deformation at the tissue level. Higher microfibril angles and helical cavities on the cell wall in compression wood correlate with a lower shrinking/swelling ratio. Normal wood showed a more pronounced swelling hysteresis than compression wood, while the sorption hysteresis was almost the same for both wood types. This finding is helpful to elucidate effects of micro- and ultrastructure on sorption. The present findings suggest that the sophisticated system of wood has the abilities to adjust the hygroscopic deformations by fine-tuning its hierarchical structures.

Hygrothermal recovery of compression wood in relation to DMSO swelling and drying shrinkage

To understand the irreversible dimensional changes caused by hygrothermal treatment of green wood, i.e. hygrothermal recovery (HTR), green hinoki compression wood (CW) and normal wood (NW) were hygrothermally (HT) treated in water at 100°C for 120 min and their HTR strains were determined. The specimens were then swollen using dimethyl sulfoxide (DMSO) and then completely dried after solvent exchange with water at room temperature. Their HTR strains were then compared with their DMSO swelling and drying shrinkage strains. The volumetric HTR strains in the CW were about twice as large as those in the NW. Moreover, the microfibril angle (MFA) was found to be an important factor for controlling the HTR intensity. A clear commonality between the HTR behavior and both DMSO swelling and drying shrinkage behavior was identified, which indicates that HTR is caused by volumetric changes in the matrix substances. HTR has been defined as a phenomenon due to the release of locked-in growth stress when a wood specimen is HT treated. To determine whether DMSO treatment has a similar effect as hygrothermal treatment, both HT-untreated and HT-treated specimens were swollen using DMSO, and their dimensional changes during and after DMSO treatment were compared. The results showed that DMSO treatment is a possible alternative for releasing the locked-in growth stress.

Contribution of lignin to the stress transfer in compression wood viewed by tensile FTIR loading

To achieve efficient utilization of compression wood (CW), a deeper insight into the molecular interactions is necessary. In particular, the role of lignin in the wood needs to be better understood, especially concerning how lignin contributes to its mechanical properties. For this reason, the properties of CW and normal wood (NW) from Chinese fir (Cunninghamia lanceolata) have been studied on a molecular scale by means of polarized Fourier transform infrared (FTIR) spectroscopy, under both static and dynamic loading conditions. Under static tensile loading, only molecular deformations of cellulose were observed in both CW and NW. No participation of lignin could be detected. In relation to the macroscopic strain, the molecular deformation of the cellulose C-O-C bond was greater in NW than in CW as a reflection of the higher microfibril angle and the lower load taken up by CW. Under dynamic deformation, a larger contribution of the lignin to stress transfer was detected in CW; the molecular deformation of the lignin being highly related to the amplitude of the applied stress. Correlation analysis indicated that there was a direct coupling between lignin and cellulose in CW, but there was no evidence of such a direct coupling in NW.

Compression wood has a minor effect on the climate signal in tree-ring stable isotope records of montane Norway spruce

Compression wood (CW) is a common tissue present in the trunk, branches and roots of mechanically stressed coniferous trees. Its main role is to increase the mechanical strength and regain the vertical orientation of a leaning stem. Compression wood is thought to influence the climate signal in different tree-ring measures. Hence trees containing CW are mostly excluded from tree-ring studies reconstructing past climate variability. There is a large gap of systematic work testing the potential effect of CW on the strength of the climate signal in different tree-ring parameters, especially stable isotope records. Here we test for the first time the effect of CW contained in montane Norway spruce (Picea abies L. Karst) on both δ13C and δ18O tree-ring cellulose records by analyzing compression and opposite wood radii from several disturbed trees together with samples from undisturbed reference trees. We selected four trees tilted by geomorphic processes that were felled by wind and four undisturbed reference trees in the Tatra Mountains, Poland. We qualitatively classified the strength of CW using wood cell anatomical characteristics (tracheid shape, cell wall thickness and presence of intercellular spaces). Then we developed tree-ring width and δ13C and δ18O chronologies from the CW radii, from the opposite radii of the tilted trees and from the reference radii. We tested the effect of CW on tree-ring cellulose δ13C and δ18O variability and on the climate signal strength. We found only minor differences in the means of δ13C and δ18O of compression (δ13C: −22.81‰, δ18O: 28.29‰), opposite (δ13C: −23.02‰; δ18O: 28.05‰) and reference (δ13C: −22.78‰; δ18O: 27.61‰) radii. The statistical relationships between climate variables, δ13C and δ18O, remained consistent among all chronologies. Our findings suggest that moderately tilted trees containing CW can be used to reconstruct past geomorphic activity and for stable isotope-based dendroclimatology.

Compression wood has a minor effect on the climate signal in tree-ring stable isotopes of montane Norway spruce

<p>Compression wood is a common tissue present in the trunk, branches and roots of mechanically stressed coniferous trees. Its main role is to increase the mechanical strength and regain the vertical orientation of a leaning stem. Compression wood is thought to influence the climate signal in different tree-ring measures. Hence trees containing compression wood are mostly excluded from tree-ring studies reconstructing past climate variability. There is a large gap of systematic work testing the potential effect of compression wood on the strength of the climate signal in different tree-ring parameters, and especially stable isotope records.</p><p>Here we test for the first time the effect of compression wood contained in montane Norway spruce (Picea abies L. Karst) on both δ<sup>13</sup>C and δ<sup>18</sup>O tree-ring cellulose records by analyzing compression and opposite wood radii from several disturbed trees together with samples from undisturbed reference trees. We selected four trees tilted by geomorphic processes that were felled by wind, and four undisturbed reference trees in the Tatra Mountains, Poland. We qualitatively classified the strength of compression wood using wood cell anatomical characteristics (tracheid shape, cell wall thickness and presence of intercellular spaces). Then we developed tree-ring width, δ<sup>13</sup>C and δ<sup>18</sup>O chronologies from the compression wood radii and the opposite radii of the tilted trees, and from the radii of the reference trees. We tested the effect of compression wood on tree-ring cellulose δ<sup>13</sup>C and δ<sup>18</sup>O variability and on the climate signal strength. Only minor differences were found in the means of δ<sup>13</sup>C and δ<sup>18</sup>O compression, opposite and reference radii. The statistical relationships between climate variables, δ<sup>13</sup>C and δ<sup>18</sup>O remained consistent among all chronologies. Our findings suggest that moderately tilted trees containing compression wood can be used to both reconstruct past geomorphic activity, and stable-isotope based dendroclimatological research.</p>

Cross-field pitting characteristics of compression, lateral, and opposite wood in the stem wood of Ginkgo biloba and Pinus densiflora

The characteristics of cross-field pitting among compression wood, lateral wood, and opposite wood, in the stem woods of Ginkgo biloba and Pinus densiflora were investigated with optical and scanning electron microscopy. In Ginkgo biloba, compression wood exhibited piceoid pits, while lateral and opposite wood exhibited cupressoid pits. The compression wood of Pinus densiflora exhibited cupressoid pits and piceoid pits, while lateral wood and opposite wood exhibited pinoid and window-like pits in the cross-field. In both species, compression wood yielded the smallest pit number among each part, while opposite wood yielded the greatest pit number per cross-field. Cross-field pitting diameters of compression wood and opposite wood were significantly smaller than lateral wood in Ginkgo biloba, while the cross-field pitting of compression wood was the smallest in Pinus densiflora. Radial tracheid diameter of compression wood was slightly smaller than lateral and opposite wood in Ginkgo biloba and significantly smaller than lateral and opposite wood in Pinus densiflora. In conclusion, the cross-field pitting type, pit number, and cross-field pitting diameter could be used to identify reaction wood in the stem wood of Ginkgo biloba and Pinus densiflora.

Influence of the p-hydroxyphenyl/guaiacyl ratio on the biphenyl and β-5 contents in compression wood lignins

Reaction woods of three softwoods, Pinus merkusii, Cryptomeria japonica and Cedrus deodara, were investigated by alkaline nitrobenzene oxidation (NBO) to characterize the condensed-type structures in compression wood lignins. A novel biphenyl-type NBO product carrying guaiacyl (G)- and p-hydroxyphenyl (H)-units, dehydrovanillin-p-hydroxybenzaldehyde (HG-biphenyl product), was identified using the authentic standard compound. On the basis of the yield of this novel NBO product, as well as those of GG-biphenyl-, β-5-, and uncondensed-type products [e.g. dehydrodivanillin, 5-formylvanillin, vanillin and p-hydroxybenzaldehyde], the compression wood lignins contained more HG-type biphenyl and H-type β-5 structures than the opposite wood lignins. The increase in the condensed-type structure content was largely offset by the decreases in the content of GG-biphenyl and G-type β-5 structures. Consequently, the relative yields of biphenyl, β-5 and uncondensed-type NBO products were very similar between the compression wood and the opposite wood, even though the H-unit having no methoxy group on its aromatic ring can be assumed to have a greater probability to form condensed-type structures during lignin biosynthesis than the G-unit.