Micro- and Nano-Scales Three-Dimensional Characterisation of Softwood

Understanding the mechanical response of cellular biological materials to environmental stimuli is of fundamental importance from an engineering perspective in composites. To provide a deep understanding of their behaviour, an exhaustive analytical and experimental protocol is required. Attention is focused on softwood but the approach can be applied to a range of cellular materials. This work presents a new non-invasive multi-scale approach for the investigation of the hygro-mechanical behaviour of softwood. At the TOMCAT beamline of the Paul Scherrer Institute, in Switzerland, the swelling behaviour of softwood was probed at the cellular and sub-cellular scales by means of 3D high-resolution phase-contrast X-ray imaging. At the cellular scale, new findings in the anisotropic and reversible swelling behaviour of softwood and in the origin of swelling hysteresis of porous materials are explained from a mechanical perspective. However, the mechanical and moisture properties of wood highly depend on sub-cellular features of the wood cell wall, such as bordered pits, yielding local deformations during a full hygroscopic loading protocol.

Cedroxylon shakhtnaense (Blokhina 2010) Dolezych, Mantzouka et L.Kunzmann comb. nov.; A fossil Abies wood from the late early Miocene Mastixioideae flora of Wiesa (east Germany)

We describe the first evidence of fossil Abies wood from the late early Miocene fossil plant assemblage of Wiesa in east Germany. The comparatively well-preserved piece of xylitic wood was recovered in the kaolin quarry at Hasenberg hill in Wiesa. The Wiesa assemblage is characterized as being allochthonous and partly parautochthonous mass deposits of diaspores, leaves, and wood. The latter component is rather incompletely studied so far. The described fossil is characterized by high rays, mostly uniseriate bordered pits, generally thick and pitted horizontal and tangential ray cell walls, but also partly smooth horizontal ray cell walls, absence of ray tracheids, the occurrence of traumatic resin canals, and rare occurrence of axial parenchyma of two types. This type of fossil wood has been described as Abietoxylon shakhtnaense Blokhina from the Oligo-Miocene of Sakhalin, Russia. Due to nomenclatural issues of Abietoxylon a recombination to Cedroxylon Kraus emend. Gothan is proposed following common practice for affiliation of abietoid fossil wood of Cenozoic age. Cedroxylon shakhtnaense comb. nov. shares anatomical characteristics with the wood of extant Abies Mill., in particular with sections Abies and Grandis, and is most closely related to section Grandis. The properly preserved fossil wood from Wiesa provides the opportunity of applying qualitative and quantitative analyses for testing and discussing its placement in relationship to intra-tree variability and ontogenetic aspects. The first evidence of fossil wood of Abies from Wiesa confirms again the presence of the genus in mid-latitude subtropical zonal vegetation during the beginning of the Miocene Climatic Optimum.

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.

Qualitative Anatomical Characteristics of Compression, Lateral, and Opposite Woods in Pinus merkusii and Agathis loranthifolia

This study aimed to observe andcompare the qualitative anatomical characteristics of compression (CW), lateral (LW), and opposite (OW) woodsin the stem wood of Sumatran pine (Pinus merkusii) and Agathis (Agathis loranthifolia). The anatomical characteristics were observed using optical microscopy and scanning electron microscopy. CW showed a gradual transition from earlywood to latewood in both species, circular tracheid shape, many intercellular spaces, irregular tracheid tips, helical cavities, and slit-like bordered pits. CW of Sumatran pine showed an indistinct growth ring, whileCW of Agathis showed a distinct growth ring. Helical ribs occurred only in CW of Sumatran pine. LW and OW showed an oval tracheid with an angular outline, regular tracheid arrangement, and tapered tracheid tips in both species. LW and OW showed mainly uniseriate bordered pits in Sumatran pine, while LW and OW of Agathis frequently showed multiseriatebordered pits. CW, LW, and OW showed fusiform and uniseriate rays in Sumatran pine, while those of Agathis showed uniseriate rays. In conclusion, CW showed distinctive qualitative anatomical characteristics to LW and OW in both species, while LW and OW mainly showed similar characteristics. In particular, there were considerably distinctive characteristics between CW from both species.Keywords: Agathis, anatomical characteristics, reaction wood, Sumatran pine

Analysis of the Structure and Hydraulic Function of Bordered Pits Using the Lattice Boltzman Method

Fluid flow between adjacent tracheids is realized through bordered pits in the xylem of conifers. The pit has an extremely small size and a highly complex structure. This paper presents a mesoscopic analytical method for the relationship between the pit structure and its hydraulic characteristics through mathematical modeling using the lattice Boltzmann method (LBM) and curved boundary treatment. Mongolian Scots pine were selected as the research subject of this study, and the bordered pit structure parameters was collected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the original geometric features were maintained for direct modeling analysis. The model revealed the relationship between various components of the bordered pit and liquid flow velocity/resistance, indicating that margo is the main factor affecting flow resistance. Further anatomical investigation separately analyzed the influence of change in a single factor, including pit diameter, pit aperture diameter, pit depth, torus diameter, and margo thickness, on the overall flow and pressure drop to confirm the importance of various factors in this relationship. Additionally, the influence of pore size and pore location distribution in the margo on the flow rate and pressure drop was further analyzed quantitatively. The results showed that the flow rate through individual pores is the result of the combined effect of pore area and radial position of the pore in the margo. Our study promotes the research and application of the mesoscopic model LBM in simulating flow conditions in the complex flow field of pits, which realizes the numerical analysis of the flow field model based on individualized real bordered pits. In comparison with the classical macroscopic model, the accuracy and effectiveness of the proposed model are proved. This research can provide a promising method for analyzing the physiological and ecological functions of conifer and realizing the efficient utilization of wood resources.

Theoretical determination of pit membrane natural frequency for destruction by resonance effect

The low permeability of many wood species causes significant problems during processing. Industrial methods used for increasing wood permeability reduce strength properties, are energy consuming, and are not viable economically. Destruction of pit membranes in wood cell walls can provide an increase in wood permeability without affecting wood strength properties. It can be accomplished using resonance applied to the pit membranes. Theoretical analysis and calculations have been performed to determine pit membrane (torus and margo) natural frequency. Membrane natural frequencies of bordered pits of Norway spruce are in the range of 3 to 11 MHz. Water in the pit chamber did not have a significant effect on the resonant frequency of the membrane. The main limitation of the amplitude of membrane fluctuations inside the pit chamber was the width of the chamber. Two methods to initiate resonance frequency for pit membrane destruction have been suggested, namely, alternating electric field application and microwave energy pulsation.

A Method for Accelerated Natural Weathering of Wood Subsurface and Its Multilevel Characterization

The function of altering weathering factors and degradation mechanisms are essential for understanding the weathering process of materials. The goal of this work was to develop a method for the acceleration of natural weathering and to investigate the molecular, microstructure and macrostructure degradation of wood caused by the process. Tests were performed in the whole month of July, which, according to previous research, is considered as the most severe for weathering of wood micro-sections. Sample appearance was evaluated by colour measurement. Scanning electron microscopy was used for evaluation of the structural integrity and changes in the microstructure of wood morphological components. Changes on the molecular level were assessed by means of FT-IR spectroscopy. Observation of the effects of weathering allowed a better understanding of the degradation process. Typical structural damage, such as cracks on bordered pits and cross-field pits, and, as a consequence, their erosion, revealed the sequence of the degradation process. It was confirmed that earlywood was more susceptible to damage than latewood. Even if the weathering test was conducted for a relatively short time (28 days) the ultra-thin wood samples changed noticeably. The progress of alteration was similar as usually noticed for wood surfaces, but occurred at shorter exposure times. The estimated acceleration factor was ×3, compare to the natural weathering kinetics of wood. The research methodology presented can be used for the determination of the weather dose-response models essential to estimate the future service life performance of timber elements.

Wood and bark anatomy of South African Picrodendraceae with systematic and ecological implications

Wood and bark structure of Androstachys johnsonii and Hyaenanche globosa (Picrodendraceae) is described. Two species share simple perforation plates, minute to small intervessel pits, and nonseptate fibres; these traits also reported in other Picrodendraceae. Androstachys is distinctive in having scanty paratracheal axial parenchyma and uniseriate rays with vessel-ray pits restricted to marginal cells. Bordered pits on fibre walls is an ancestral condition for the African Picrodendraceae. High vessel frequency and vessel grouping in Androstachys can be adaptive for semi-arid climate with wet summer. Both genera share the subepidermal phellogen initiation and the presence of thick-walled fibers and sclereids in secondary phloem. In Hyaenanche, the bark is dilated by stretching and divisions of parenchyma cells with formation of pseudocortex. Androstachys shows no ray dilatation, but sclerification of its parenchyma can make substantial contribution in bark expansion. Abundant trichomes on epidermis of young shoots of Androstachys are presumably involved in the water uptake from mists.

Isometric scaling to model water transport in conifer tree rings across time and environments

Xylem hydraulic properties determine the ability of plants to efficiently and safely provide water to their leaves. These properties are key to understanding plant responses to environmental conditions and to evaluating their fate under a rapidly changing climate. However, their assessment is hindered by the challenges of quantifying basic hydraulic components such as bordered pits and tracheids. Here we use isometric scaling between tracheids and pits morphology to merge partial hydraulic models of tracheid’s component to upscale properties at the tree-ring level in conifers trees. Our new model output is first cross-validated with literature and then applied to cell anatomical measurements from Larix sibirica tree-rings formed under harsh conditions in southern Siberia to quantify the intra- and inter-annual variability in hydraulic properties. The model provides a means of assessing how different-sized tracheid’s components contribute to the hydraulic properties of the ring. Up-scaled results indicate that natural inter- and intra-ring anatomical variations have a substantial impact on the tree’s hydraulic properties. Our model facilitates the assessment of important xylem functional attributes because it only requires the more accessible measures of cross-sectional tracheid size. This approach, if applied to dated tree-rings, provides a novel way to investigate xylem structure-function relations across time and environmental conditions.