Tracheid Cell Walls Research Articles

Effect of High-Intensity Microwave Treatment on Structural and Chemical Characteristics of Chinese Fir

High-intensity microwave (HIMW) treatment is a time-saving and environmentally friendly method widely applied in the wood processing industry. It enhances wood permeability, making it suitable for drying and impregnation modification. This study aimed to investigate the effects of HIMW on macroscopic and microscopic cracks, tracheid cell wall damage, and the chemical structure of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] wood. Through the use of a camera, optical microscope, scanning electron microscope, transmission electron microscope, Fourier-transform infrared spectroscopy, and X-ray diffraction, the morphology of cracks, cell wall damage, the chemical composition of the cell wall, and the crystalline structure of cellulose treated with HIMW were examined and analyzed. The results revealed that the initial moisture content (MC) and microwave energy density (MWED) significantly influenced the crack characteristics and cell wall structure and slightly influenced the chemical composition and crystalline structure of cellulose of the Chinese fir cell wall. HIMW treatment can produce different characteristics of wood cracks. The size and number of cracks were significantly increased with the increase in MWED, and more cracks were found in low MC. Microcracks caused by HIMW treatment tended to initiate at the ray parenchyma, resulting in the stripping of ray cells along its radial direction. Meanwhile, the cracking of adjacent cell junctions, the rupturing of the pit margo and pit torus, and cell wall parts tearing along the direction of microfibers occurred as a result of the HIMW treatment. The most severe damage to the cell walls occurred at the interface of S1/S2, S1, and ML layers, and the cell walls were torn in the S2 layer. There were no significant changes in the FTIR spectra of the HIMW treatment samples. Hemicellulose degradation occurred first, which increased with the increase in MWED. The recrystallization of cellulose and the lignin content increased because of the change in the aromatic C=O groups. As MWED increased, both the crystallinity index (CI) and cellulose crystal width (D200) of the samples that underwent HIMW treatment increased accordingly, and the number of low-MC samples was greater than that of the high-MC samples. The findings contribute to understanding the crack characteristics and damage mechanism induced by HIMW treatment on wood. This study provides valuable insights into regulating the effects of HIMW treatment and expanding its application in wood processing, such as wood drying and functionalized impregnation, according to the specific end-use requirements.

Biological decay by microorganisms in stems from the Upper Triassic Ischigualasto Formation (San Juan Province, Argentina): A striking microbial diversity in Carnian-Norian terrestrial ecosystems

We studied degradation patterns and microorganisms preserved in permineralized stems of Rhexoxylon piatnitzky, Protojuniperoxylon ischigualastense, and Agathoxylon argentinum from the Valle de la Luna Member of the Ischigualasto Formation (Upper Triassic, San Juan, Argentina). All three species show loss of middle lamella, thinning, and whitening of tracheid cell walls, and detachment of the S3 layer, consistent with selective delignification by white rot. This type of rot is the product of lignin and cellulosic degradation by Basidiomycetes and Ascomycetes. Rhexoxylon piatnitzkyi also shows small cavities, more or less circular in outline, on the wall of tracheids. This is known as soft rot and can be produced by some Ascomycetes, the anamorphic phases of diverse fungi, and tunneling bacteria. Additionally, abundant and diverse microorganisms were found. Rhexoxylon piatnitzkyi shows fragments of septate hyphae, evidence of bacterial activity, and structures of unknown affinity. Protojuniperoxylon ischigualastense presents structures common to anamorphic phases of diverse fungi, such as chlamydospores and conidiophores. Lastly, Agathoxylon argentinum bears coiled and septate hyphae, and a fan-shaped mycelium, whose significance is discussed. The microbiological study was complemented by the assessment of sedimentary and taphonomic data of the fossil-bearing beds. A gradual increment in humidity for the Valle de la Luna Member is interpreted, which concludes with a humidity peak in its upper section. This contribution represents the first detailed study of xylophagous and saprophyte micro-communities for the Ischigualasto Formation. The abundance and diversity of microorganisms described illustrate the complexity of wood-inhabiting micro-communities from the Carnian-Norian interval of Argentina.

Deterioration of Microstructures and Properties in Ancient Architectural Wood from Yingxian Wooden Pagoda (1056 AD) during Natural Aging

The Yingxian Wooden Pagoda (1056 AD), located in Shanxi province, China, is a unique architectural pure-wooden artifact standing for a millennium. Despite its longevity, the structures and properties of the ancient architectural woods used in its construction have been significantly degraded due to long-term natural aging, which has profoundly impacted the preservation of this valuable cultural heritage. To better understand this degradation, we studied the deterioration of a baluster (Larix principis-rupprechtii Mayr.) from Yingxian Wooden Pagoda. The study employed various analytical techniques, including optical microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, X-ray diffraction, and nanoindentation technology, to evaluate the microstructures and properties of the ancient architectural woods. Results indicated that the destruction of wood cell walls was primarily transverse transwall destruction and interfacial debonding and that the degradation of chemical components was primarily in the hemicellulose (xylan) and amorphous region of cellulose. The reduced elastic modulus and hardness of tracheid cell walls in the ancient architectural woods were higher than in recent larch woods. This study would help deepen understanding of wood deterioration during long-term natural aging for the subsequent preservation and protection of wooden cultural heritages and longer use of ancient timber constructions.

Microwave Drying of Scots Pine Lumber: Structure Changes, Its Effect on Liquid Permeability

Microwave (MW) drying method was adopted to enhance the liquid permeability of Scots pine lumber. Structure changes were characterized by stereoscope microscope, scanned electron microscope (SEM) and transmission electron microscope (TEM) examination. Pore parameters before and after MW treatment were detected by mercury intrusion porosimetry (MIP) method, and the effect of structure changes on liquid permeability were analyzed. As stereoscope microscope, SEM and TEM examination results shown, macro and micro checks mainly developed at intercellcular of tracheids, intercellular of ray parenchyma and tracheid, while these checks extend main along the radial-longitudinal plane. Pit border destruction, aspirated pits’ orus translocation and micro-checks in tracheid cell wall were also observed. MIP test shown that pore volume and pore area increased as macro and micro checks generated to form new cavities. Microstructure changes would increase the quantity of pores or enlarge the pore diameter. Liquid flow pathways increased as macro and micro checks generated, aspirated pits reopened to form new pathways; liquid flow efficiency improved as porosity, pore volume and pore diameter increase which facilitate the liquid flow.

Response of Tracheid Structure Characteristics and Lignin Distribution of Taxodium Hybrid Zhongshanshan to External Stress

The Taxodium hybrid Zhongshanshan fast-growing species is susceptible to environment and gravity to form reaction wood. In this study, individual growth rings of reaction wood are used as subjects, and an individual growth ring is divided into three zones: compression zone (CZ), lateral zone (LZ), and opposite zone (OZ). The microanatomical structure and chemical properties of the tracheids in CZ, LZ, and OZ forms by the inclined or bent growth of T. Zhongshanshan are comparatively analyzed by using optical microscopy, scanning electron microscope, laser confocal microscopy, and Raman imaging techniques. In CZ, the length and diameter of compression wood (CW) tracheids decreased, and the shape of cross-sections became rounded as compared to the OZ and LZ tracheids. More notably, threaded fissures appeared on the cell wall of tracheids, and the thickness of the cell wall increased in CW. The analysis of tracheids’ cell wall structure showed that CW tracheids had a complete outer secondary wall middle (S2L) layer, but had no secondary wall inner (S3) layer. In the transition zone (TA) between CW and normal early wood, tracheids were divided into compressed and normal tracheids. Despite the compressed tracheids having a similar cell morphology to normal tracheids, they had a thin secondary wall S2L layer. Tracheids in LZ had a thin S2L layer only at the angle of the cell. No S2L layer was seen in the cell wall of OZ and CZ late wood tracheids. It can be concluded that the response of lignin deposition location to external stress was faster than the change in cell morphology. The above results help provide the theoretical basis for the response mechanism of T. Zhongshanshan reaction wood anatomical structures to the external environment and has important theoretical value for understanding its characteristics and its rational and efficient usage.

Quantitative studies on charcoalification: Physical and chemical changes of charring wood

Charcoal is commonly preserved in both natural and artificial sediments, and is intensively used in paleontological, paleoenvironmental, and archaeological studies due to the abundant bio-information it contains. The biochemical properties of charcoal are also used for paleoclimatic reconstruction; however, the reliability of this approach has been challenged due to a lack of clarity on how physicochemical properties change during the charring process, as well as the temperatures required for charcoalification. To address this lack, in this study, Qinghai spruce and Chinese pine wood samples from the northeastern Tibetan Plateau were heated at different temperatures and for different lengths of time under restricted oxygen conditions. The reflectance; carbon, nitrogen, and oxygen content; and tracheid morphology were quantified before and after heating to assess changes related to the charring process. Archaeological charcoal remains were then evaluated to determine the charcoalification temperatures by comparing with the experimental results. The minimum temperature required for wood charcoalification was ∼300 °C, while temperatures recorded by archaeological charcoal were concentrated at 400–500 °C. During the charring experiments, the tracheid cell walls gradually homogenized, and tracheid cell wall thickness and lumen area decreased by ∼20%. On average, 50% mass losses were observed; the carbon and oxygen content (% wt.) approximately changed from 47% to 60% and 48% to 35% respectively, while the nitrogen content (% wt.) fluctuated around 0.2%. The reflectance increased slightly from 0% to 0.5%. We propose that the charcoalification of wood tissue refers to charring (in restricted air) and carbonization (in the almost absence of air) when the wood is exposed to a heat source, which then finally transforms into a black, inert solid. This quantitative study provided valuable data and a thorough assessment of the process of wood charcoalification, as well as accurately estimated the feasibility of using charcoal physicochemical properties in paleoclimatic research.

Enzymatic treatments for improved dyeing of solid wood

Abstract Full penetration-dyed solid wood has the advantage that furniture or other items fabricated from it do not require additional painting or staining. However, anatomical barriers along potential dye infiltration pathways may result in unsatisfactory dyeing in terms of depth of dye penetration or colour intensity and uniformity. Dyed wood items, even those intended for interior use, should also possess a certain degree of water fastness. In the present paper, full-thickness dyeing of radiata pine blocks was achieved with fibre-reactive and direct dyes as well as pine tannin. Leaching of the treated blocks in cold water removed excess dye but the target colours were well retained. Pectinase pre-treatment of wood blocks was shown to increase the uptake of fibre-reactive and direct dyes by tracheid cell walls and the uptake of tannin by rays, resin canals, and tracheid lumina. In the case of a direct dye and pine tannin, pectinase treatment markedly increased the intensity of the target colours. Combining tannin with laccase to achieve covalent bonding of tannin to wood lignin was associated with a small, albeit not statistically significant, shift towards the target colour.

Determination of charring thickness of wood by residual strength analysis

This study was conducted to propose an accurate measurement method of charred thickness in structural glued laminated timber (glulam) exposed to standardized fire temperature conditions for evaluation of the fire resistance of Japanese larch (Larix kaempferi) structural glulam. The compressive strength of the test piece collected from the structural glulam exposed to the standardized fire temperature for two hours was analyzed. The results showed that there was residual strength of 14% in the boundary area between sound and charred part. Therefore, the thickness of charred part should be calculated as approximately 4.5 mm less than what is measured visually. The cell wall thickness between sound-, boundary-, and charred-part exposed to high temperature was observed under a microscope. Higher temperature resulted in a thinner tracheid cell wall, and the radial tissue was broken down. The transformation of the boundary part of these microstructures progressed gradually until full carbonization of wood occurred. Based on compressive strength tests and microscopic observation in the boundary part of specimens exposed to high temperature, the current visual assessment of charred thickness measurement is safe in terms of structural aspect but not efficient in terms of wood utilization point of view due to exception of load carrying area of the member.

Study of the Mechanical Properties of Wood under Transverse Compression Using Monto Carlo Simulation-Based Stochastic FE Analysis

Wood is an anisotropic material, the mechanical properties of which are strongly influenced by its microstructure. In wood, grain compression strength and modulus are the weakest perpendicular to the grain compared to other grain directions. FE (finite element) models have been developed to investigate the mechanical properties of wood under transverse compression. However, almost all existing models were deterministic. Thus, the variations of geometry of the cellular structure were not considered, and the statistical characteristic of the mechanical property was not involved. This study aimed to develop an approach to investigate the compression property of wood in a statistical sense by considering the irregular geometry of wood cells. First, the mechanical properties of wood under radial perpendicular to grain compression was experimentally investigated, then the statistical characteristic of cell geometry was extracted from test data. Finally, the mechanical property of wood was investigated using the finite element method in combination with the Monte Carlo Simulation (MCS) techniques using randomly generated FE models. By parameter sensitivity analysis, it was found that the occurrence of the yield points was caused by the bending or buckling of the earlywood axial tracheid cell wall in the tangential direction. The MCS-based stochastic FE analysis was revealed as an interesting approach for assessing the micro-mechanical performance of wood and in assisting in understanding the mechanical behavior of wood based on its hierarchical structure.

Pit and tracheid anatomy explain hydraulic safety but not hydraulic efficiency of 28 conifer species.

Conifers face increased drought mortality risks because of drought-induced embolism in their vascular system. Variation in embolism resistance may result from species differences in pit structure and function, as pits control the air seeding between water-transporting conduits. This study quantifies variation in embolism resistance and hydraulic conductivity for 28 conifer species grown in a 50-year-old common garden experiment and assesses the underlying mechanisms. Conifer species with a small pit aperture, high pit aperture resistance, and large valve effect were more resistant to embolism, as they all may reduce air seeding. Surprisingly, hydraulic conductivity was only negatively correlated with tracheid cell wall thickness. Embolism resistance and its underlying pit traits related to pit size and sealing were more strongly phylogenetically controlled than hydraulic conductivity and anatomical tracheid traits. Conifers differed in hydraulic safety and hydraulic efficiency, but there was no trade-off between safety and efficiency because they are driven by different xylem anatomical traits that are under different phylogenetic control.

Bordered Pit Formation in Cell Walls of Spruce Tracheids.

The process of pit formation in plants still has various questions unaddressed and unknown, which opens up many interesting and new research opportunities. The aim of this work was elucidation of the mechanism for the formation of bordered pits of the spruce (Picea abies (L.) Karst.) tracheid with exosomes participation and mechanical deformation of the cell wall. Sample sections were prepared from spruce stem samples after cryomechanical destruction with liquid nitrogen. The study methods included scanning electron microscopy and enzymatic treatment. Enzymatic treatment of the elements of the bordered pit made it possible to clarify the localization of cellulose and pectin. SEM images of intermediate stages of bordered pit formation in the radial and tangential directions were obtained. An asynchronous mechanism of formation of bordered-pit pairs in tracheids is proposed. The formation of the pit pair begins from the side of the initiator cell and is associated with enzymatic hydrolysis of the secondary cell wall and subsequent mechanical deformation of the primary cell walls. Enzymatic hydrolysis of the S1 layer of the secondary cell wall is carried out by exosome-delivered endoglucanases.

Variations in bacterial decay between cell types and between cell wall regions in waterlogged archaeological wood excavated in the intertidal zone

Abstract The bacterial decay of waterlogged archeological wood (WAW, hard pine spp.) taken from Daebudo shipwreck No. 2, which was buried in the intertidal zone in the mid-west coast (Yellow sea) of South Korea approximately 800 years ago, was investigated. The maximum moisture content of the outer parts (approx. 3 cm of depth) of WAW was approximately 4.2 times higher than that of undegraded reference pine wood. ATR-FTIR and solid-state 13C-NMR analysis indicated a relative increase of the lignin concentration in WAW caused by the degradation of cellulose and hemicelluloses across the board studied (31-cm-wide and 14.5-cm-thick board). Micromorphological studies also revealed that bacterial degradation was progressed to a depth of 15 cm (vertically 7.3 cm) from the surface, which is the innermost part of the board. Erosion bacteria (EB) were identified as the main degraders of WAW. Degradation by tunneling bacteria (TB) was occasionally detected. Decay resistance to bacterial attacks in WAW varied between cell types and between cell wall regions. Axial tracheids showed less resistance than ray tracheids, ray parenchyma cells, and axial intercellular canal cells, including strand tracheids, subsidiary parenchyma cells, and epithelial cells. Decay resistance was higher in ray tracheids and strand tracheids than in ray parenchyma cells and subsidiary parenchyma-/epithelial cells, respectively. Bordered- and cross-field pit membranes and the initial pit borders showed higher decay resistance than the tracheid cell walls. Overall, the S2 layer of the axial tracheids showed the weakest resistance to bacterial attacks.

Ray Traits of Juvenile Wood and Mature Wood: Pinus massonia and Cunninghamia lanceolata

Ray traits affect secondary xylem development and wood properties. Pinus massonia and Cunninghamia lanceolata, commercially important timber species, were chosen to study the differences in wood ray traits of juvenile versus mature wood. Seven ray traits, i.e., percentage of rays, ray spacing, ray number, uniseriate ray height, fusiform ray height, ray parenchyma cell length and ray tracheid length, as well as eight wood axial tissue traits, were investigated quantitatively. Intraspecific variations in ray traits and axial tissue traits between juvenile wood and mature wood were displayed in violin plots. The results showed that anatomical differences between juvenile wood and mature wood were significant for both ray traits and axial tissue traits. Juvenile wood generally possessed the larger percentage of rays, higher ray spacing and ray number, smaller ray height and shorter ray cells than mature wood. A positive correlation was present between the ray parenchyma cell length and ray tracheid length. Negative correlations of the ray number and ray spacing with uniseriate ray height were found. Additionally, the axial tracheid cell wall thickness all had Pearson’s correlations with ray spacing, ray number and ray parenchyma cell length.

Tree-ring density and carbon isotope composition are early-warning signals of drought-induced mortality in the drought tolerant Canary Island pine

Tree death is not always preceded by a visible decline in vigor (canopy dieback) or a progressive loss in crown volume. Identifying early-warning signals of incipient decline can help to implement the necessary measures to prevent tree death. The aim of this work is to understand what functional alterations preceded the massive drought-induced death of adult Pinus canariensis trees in an arid stand, located in the Canary Islands. To this aim, we analyzed interannual variations in earlywood and latewood width, wood density and anatomy, and carbon isotope composition, and the relationships among these variables, in dead and living trees from 1980 to 2013. Dead trees grew less since the 1990′s, produced fewer parenchyma rays and resin canals, and exhibited a trend of decreasing latewood density and a marked shift in carbon isotope discrimination over the last 34 years that were reversed in living trees. Higher wood density in living trees resulted from thicker tracheid cell walls rather than narrower lumens. The intrinsic water use efficiency shifted from higher to lower values in dead trees after the 2000s. These results suggest a carbon limitation to maintain hydraulic safety under xylem tension, as well as to maintain storage and defense capacity, which can render trees more vulnerable to severe drought episodes. A long-term trend of decreasing tree-ring density and a reduced intrinsic water use efficiency in the short-term can be early-warning signals of carbon limitation and tree decline in drought-stressed P. canariensis. The analysis of these variables can be used to assess tree decline risks in similarly vulnerable conifer populations inhabiting drought-prone regions.

Anatomical structure and degradation characteristics of bioincised oriental spruce wood by Physisporinus vitreus

ABSTRACT Even though oriental spruce (Picea orientalis L.), a common species in the East Black Sea Region of Turkey, is used in a wide range of applications, its wood has low permeability. This study investigated the degradation effects of the bioincising process to improve its treatability with wood preservatives on the microstructure of oriental spruce wood. Test samples were previously subjected to bioincising by Physisporinus vitreus fungus, and the bioincised samples were examined under both a light microscope and scanning electron microscope to observe the effects of the bioincising on the anatomical properties. Bordered pits on the longitudinal tracheid radial walls, piceoid-type cross-field pits, ray tracheid bordered pits, and ray tracheid cell walls in the earlywood and latewood regions within a growth ring were particularly subjected to anatomical evaluations. In the study, the degradation intensity in the samples after the bioincising was well correlated with the weight losses occurred. Splits and factures were determined on the tori of bordered pits on the tracheid cell walls while tears and cracks were present on the pit apertures. The results also show that P. vitreus, a Type I and II white rot fungus, may cause a Type I soft rot.

Localised laccase activity modulates distribution of lignin polymers in gymnosperm compression wood.

Summary The woody stems of coniferous gymnosperms produce specialised compression wood to adjust the stem growth orientation in response to gravitropic stimulation. During this process, tracheids develop a compression‐wood‐specific S2L cell wall layer with lignins highly enriched with p‐hydroxyphenyl (H)‐type units derived from H‐type monolignol, whereas lignins produced in the cell walls of normal wood tracheids are exclusively composed of guaiacyl (G)‐type units from G‐type monolignol with a trace amount of H‐type units. We show that laccases, a class of lignin polymerisation enzymes, play a crucial role in the spatially organised polymerisation of H‐type and G‐type monolignols during compression wood formation in Japanese cypress (Chamaecyparis obtusa).We performed a series of chemical‐probe‐aided imaging analysis on C. obtusa compression wood cell walls, together with gene expression, protein localisation and enzymatic assays of C. obtusa laccases.Our data indicated that CoLac1 and CoLac3 with differential oxidation activities towards H‐type and G‐type monolignols were precisely localised to distinct cell wall layers in which H‐type and G‐type lignin units were preferentially produced during the development of compression wood tracheids.We propose that, not only the spatial localisation of laccases, but also their biochemical characteristics dictate the spatial patterning of lignin polymerisation in gymnosperm compression wood.

Extractive concentrations and cellular-level distributions change radially from outer to inner heartwood in Scots pine.

The heartwood of many wood species is rich in extractives, which improve the wood material's resistance to biological attack. Their concentration is generally higher in outer than inner heartwood, but the exact radial changes in aging heartwood remain poorly characterized. This investigation studied these radial changes in detail in Scots pine (Pinus sylvestris L.), using radial sample sequences prepared from three different trees. Stilbene and resin acid contents were first measured from bulk samples, after which the extractive contents of individual heartwood annual rings were investigated using Raman spectroscopy and fluorescence microscopy. Raman imaging and fluorescence microscopy were also used to study the cellular-level distributions of extractives in different annual rings. Although there were substantial differences between the trees, the content and distribution of stilbenes seemed to follow a general radial trend. The results suggest that stilbenes are absorbed into heartwood tracheid cell walls from small stilbene-rich extractive deposits over several years and then eventually transform into non-extractable compounds in aging heartwood. Resin acids followed no consistent radial trends, but their content was strongly connected to the frequency of large extractive deposits in latewood tracheid lumens. The results highlight the variability of heartwood extractives: their content and distribution vary not only between trees but also between and even within the annual rings of a single tree. This high variability is likely to have important effects on the properties of heartwood and the utilization of heartwood timber.

Effects of Microwave Treatment on Microstructure of Chinese Fir

Microwave (MW) treatment is an effective method to increase refractory wood permeability, thereby reducing drying time and defects. The extent of modification depends on the damage extent of the wood microstructure. In this study, MW intensities of 43 kWh/m3 (low intensity) and 57 kWh/m3(high intensity) were adopted to treat Chinese fir lumber. Microstructural changes in wood samples were observed using scanning electron microscopy (SEM) and pore structure was characterized using mercury intrusion porosimetry (MIP). Results were as follows: After low-intensity MW treatment, parts of the bordered pit membranes in tracheids were damaged, and micro-fibrils on the margo were ruptured, while the torus basically remained intact. Micro-cracks were observed at both ends of the cross-field pit apertures, propagating to the cell walls of tracheids. The middle lamellar between ray parenchyma cells and longitudinal tracheids cracked, and the width of cracks was in the range of 1–25 μm. After high-intensity MW treatment, damage to the wood microstructure was more severe than that in the low-intensity MW treatment, with macro-cracks having a width range of 100–130 μm being generated. In addition, on the fracture surface of macro-cracks, the bordered pit membranes in tracheids fell off, cross-field pit membranes disappeared and the ray parenchyma cells were seriously damaged, exhibiting fracture of the tracheid walls. Both low-intensity and high-intensity MW treatment can increase the pore diameter corresponding to the margo capillaries (peak value increased from 674.7 nm to 831.8 nm and 1047.6 nm, respectively). The number of pores in the tracheid lumen diameter range also significantly increased. These results provide a theoretical support forMW treatment processes’ improvement and high-value utilization of Chinese fir.

Hyperspectral Near-Infrared Image Assessment of Surface-Acetylated Solid Wood.

Visualization of acetic anhydride flow and its heterogeneity within the wood block necessitates the development of a reliable and robust analytical method. Hyperspectral imaging has the potential to acquire a continuous spectrum of chemical analytes at different spectral channels in terms of pixels. The large set of chemical data (3-dimensional) can be expanded into relevant information in a multivariate fashion. We quantified gradients in acetylation degree over cross sections of Scots pine sapwood caused by a one-sided flow of acetic anhydride into wood blocks using near-infrared hyperspectral imaging. A principal component analysis (PCA) model was used to decompose the high-dimensional data into orthogonal components. Moreover, a partial least-squares (PLS) hyperspectral image regression model was developed to quantify heterogeneity in acetylation degree that was affected by the flow of acetic anhydride through wood blocks and into the tracheid cell walls. The model was validated and optimized with an external test data set and a prediction map using the root-mean-squared error of an individual predicted pixel. The model performance parameters are well suited, and prediction of the acetylation degree at the image level was complemented with confocal Raman imaging of selected areas on the microlevel. NIR image regression showed that the acetylation degree was determined not only by the time-dependent flow of the acetic anhydride through the wood macropores but also by the diffusion of the anhydride into the wood cell walls. Thereby, thin-walled earlywood sections were acetylated faster than the thick-walled latewood sections. Our results demonstrate the suitability of near-infrared imaging as a tool for quality control and process optimization at the industrial scale.

Woody charcoal with traces of pre-charring decay from the Late Oligocene (Chattian) of Norken (Westerwald, Rhineland-Palatinate, W Germany)

A variety of traces of pre-charring decay are described from coniferous charcoals from the Norken locality, stratigraphically positioned within the Breitscheid Formation (Late Oligocene, Chattian) of the Westerwald area (Rhineland-Palatinate; W Germany). The traces include three-dimensionally preserved as well as collapsed fungal hyphae, collapsed filamentous structures (maybe related to ascomycetes), so-called shot-like holes of different diameters in cell walls of tracheids, as well as crater-like structures on the surface of tracheid walls. The latter occur on tracheids with bordered pits, in the direct vicinity of charred phloem (so far only rarely reported from pre-Quaternary charcoal). These observations, together with evidence that some of the charcoal fragments originated from wood that dried out prior to charring, point to a surface fire as the most likely source of the charcoal, although it cannot totally be ruled out that (partly) dead but still standing trees were affected during a crown fire. The data from the Late Oligocene of Norken provide further evidence that pre-Quaternary charcoal can be used as an additional, so far largely underutilized source for additional information about plant– microorganism interactions in deep time.