Latewood Cell Wall Research Articles

Dynamic structural evolution of lignin macromolecules and hemicelluloses during Chinese pine growth

To comprehend the biosynthesis processes of conifers, it is essential to investigate the disparity between the cell wall shape and the interior chemical structures of polymers throughout the development of Chinese pine. In this study, branches of mature Chinese pine were separated according to their growth time (2, 4, 6, 8 and 10 years). The variation of cell wall morphology and lignin distribution was comprehensively monitored by scanning electron microscopy (SEM) and confocal Raman microscopy (CRM), respectively. Moreover, the chemical structures of lignin and alkali-extracted hemicelluloses were extensively characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The thickness of latewood cell walls increased steadily from 1.29 μm to 3.38 μm, and the structure of the cell wall components became more complicated as the growth time increased. Based on the structural analysis, it was found that the content of β-O-4 (39.88–45.44/100 Ar), β-β (3.20–10.02/100 Ar) and β-5 (8.09–15.35/100 Ar) linkages as well as the degree of polymerization of lignin increased with the growth time. The complication propensity increased significantly over 6 years before slowing to a trickle over 8 and 10 years. Furthermore, alkali-extracted hemicelluloses of Chinese pine mainly consist of galactoglucomannans and arabinoglucuronxylan, in which the relative content of galactoglucomannans increased with the growth of the pine, especially from 6 to 10 years.

Effect of Vacuum Heat Treatment on Larch Earlywood and Latewood Cell Wall Properties

The aim of this study was to evaluate the hygroscopicity and nanomechanics of earlywood (EW) and latewood (LW) larch after thermal modification under vacuum conditions. Wood samples were heat-treated in a vacuum atmosphere at 180–220 °C for 6 h, then their cell wall properties were observed using dynamic water vapor sorption (DVS), imaging Fourier-transform infrared (FTIR) microscopy, and nanoindentation. The results showed that the vacuum heat treatment reduced the hygroscopicity of EW and LW and increased hysteresis between the adsorption and desorption branches of the isotherm. Compared with EW, the treatment temperature had a more pronounced influence on the hygroscopicity of LW. The Hailwood-Horrobin model was found to accurately fit the experimental data. Imaging FTIR microscopy revealed degradation of hemicellulose, cross-linking, condensation reactions, and redistribution of lignin in the cell wall. The elastic modulus for the heat-treated EW and LW cell walls increased at first and then decreased as the treatment temperature increased; the increase in LW was more intense than that in EW. Cell wall hardness also markedly increased after heat treatment. Our analysis suggests that vacuum heat treatment decreases hygroscopicity and alters the chemical composition distribution of cell walls, thus improving wood cell wall mechanics.

Characterization of wood cell walls treated by high-intensity microwaves: Effects on physicochemical structures and micromechanical properties

High-intensity microwave treatment is an environmentally friendly and time-saving method with a great potential to generate a platform for wood product innovations by increasing the permeability and providing an excellent precondition for wood modification. This work aimed to evaluate the influence of high-intensity microwaves on the physicochemical structures and micromechanical properties of wood cell walls. At the same time, the different response behavior of earlywood and latewood cell walls to microwaves was determined separately. With the help of the optical microscopic, imaging FTIR microscopy, X-ray diffractometer and nanoindenter, the characteristic of the treated cell walls, such as morphology, chemical structures, crystalline structures, hardness and elastic modulus, was thoroughly investigated. The results showed that the physicochemical structures and properties of cell walls were significantly affected by the initial moisture content and microwave intensity with the earlywood being more sensitive to microwaves than latewood. The most damaged cell wall morphology occurred with the moisture content of 20% and microwave power density of 80 kWh/m3. Compared with cellulose and lignin, the hemicellulose showed much more considerable changes in the molecular structures. The crystallinity in microwave-treated samples fluctuated and increased by 15.5% under 60 kWh/m3 microwaves. The cell wall hardness and modulus could both be enhanced, the maximum increase for the former being 48.3% and 36.5% and for the latter being 50.5% and 33.3% in earlywood and latewood, respectively. The findings obtained from this study could help elucidate the mechanism and precisely manipulate the effect of high-intensity microwave treatment, and further extend the application of the wood microwave treatment.

Thermal responses of mountain birch and Siberian larch of an alpine forest-tundra ecotone to climate change

We applied thermogravimetric analysis to ten successive growth rings of Siberian larch and the same number of mountain birch individuals sampled in the alpine forest-tundra ecotone of Kuznetsk Ala Tau mountain ridge to compare physical and chemical responses of the species wood to climate change. Our analysis of the correlation of the wood thermal parameters with air temperature and precipitation revealed that early and latewood cellulose and lignin in the birch were more sensitive to climatic changes as compared to the larch. June–August weather conditions appeared to largely control the chemical composition of the birch early and latewood. Air temperature had a marked influence during synthesis of both early and latewood cell walls, whereas precipitation influenced only latewood. Thermogravimetric analysis of growth rings formed in alpine forest-tundra proved to be an effective tool to study the influence of climatic and weather variability on lignin-carbohydrate complex of deciduous and conifer tree species.

Intra‐Annual Climate Anomalies in Northwestern North America Following the 1783–1784 CE Laki Eruption

AbstractThe 1783–1784 CE Laki eruption in Iceland was one of the largest, in terms of the mass of SO2 emitted, high‐latitude eruptions in the last millennium, but the seasonal and regional climate response was heterogeneous in space and time. Although the eruption did not begin until early June, tree‐ring maximum latewood density (MXD) reconstructions from Alaska suggest that the entire 1783 summer was extraordinarily cold. We use high‐resolution quantitative wood anatomy, climate model simulations, and proxy systems modeling to resolve the intra‐annual climate effects of the Laki eruption on temperatures over northwestern North America. We measured wood anatomical characteristics of white spruce (Picea glauca) trees from two northern Alaska sites. Earlywood cell characteristics of the 1783 ring are normal, while latewood cell wall thickness is significantly and anomalously reduced compared to non‐eruption years. Combined with complementary evidence from climate model experiments and proxy systems modeling, these features indicate an abrupt and premature cessation of cell wall thickening due to a rapid temperature decrease toward the end of the growing season. Reconstructions using conventional annual resolution MXD likely over‐estimate total growing season cooling in this year, while ring width fails to capture this abrupt late‐summer volcanic signal. Our study has implications not only for the interpretation of the climatic impacts of the Laki eruption in North America, but more broadly demonstrates the importance of timing and internal variability when comparing proxy temperature reconstructions and climate model simulations. It further demonstrates the value of developing cellular‐scale tree‐ring proxy measurements for paleoclimatology.

Hyperspectral imaging and chemometrics reveal wood acetylation on different spatial scales

Acetylation is a chemical treatment method commonly used to improve the hygroscopic properties of wood. Although acetylation has been industrially used for decades, its effects on the different hierarchical structures of wood are still poorly understood. In the laboratory, acetylation is generally measured gravimetrically. Weighing a sample before and after the modification procedure provides an indirect measure of the degree of acetylation within the entire sample but does not provide detailed information on the different structural regions of wood. Here, we determined acetylation of wood surfaces using hyperspectral near-infrared image regression. Our results show significant differences in the acetylation of earlywood and latewood, which suggests different durations for complete acetylation of earlywood and latewood cells. We have also illustrated our findings on the wood cell level based on the chemical differences in earlywood and latewood cell walls using cluster analysis of Raman images. These findings are an important step in understanding how chemical treatment affects the different hierarchical structures of wood on different spatial scales.Graphical

Small fluctuations in cell wall thickness in pine and spruce xylem: Signal from cambium?

In the conifer tree rings, each tracheid goes through three phases of differentiation before becoming an element of the stem water-conducting structure: division, extension, and cell wall thickening. These phases are long-lasting and separated temporally, especially cell wall thickening. Despite the numerous lines of evidence that external conditions affect the rate of growth processes and the final anatomical dimensions during the respective phases of tracheid differentiation, the influence of the environment on anatomical dimensions during the cell division phase (cambial activity) has not yet been experimentally confirmed. In this communication, we provide indirect evidence of such an effect through observations of the small fluctuations in the latewood cell wall thickness of rapidly growing tree rings, which exhibit a high cell production rate (more than 0.4 cells per day on average). Such small fluctuations in the cell wall thickness cannot be driven by variations in external factors during the secondary wall deposition phase, since this phase overlaps for several tens of latewood cells in the rings of fast-growing trees due to its long duration.

Tree Growth Under Climate Change: Evidence From Xylogenesis Timings and Kinetics.

Tree growth is one of the most studied aspects of tree biology, particularly secondary growth. In the Mediterranean region, cambial activity is mostly determined by water availability. Climatic projections for the Mediterranean region predict more frequent and intense droughts, and longer periods without precipitation. To investigate tree growth under the predicted scenarios of climate change, a water manipulation experiment was conducted in a maritime pine stand (Pinus pinaster Aiton). In 2017, fifteen trees were divided into three groups: control, rain exclusion, and irrigation. Drought conditions were simulated by installing a continuous plastic sheet on the forest floor from March to September. Trees under irrigation treatment were watered twice a week in September. Cambial activity and xylem formation was monitored every 10 days from February 2017 until March 2018. Cell production was maximal around the spring equinox in all treatments. Trees under rain exclusion decreased cell production rates, xylogenesis duration, and latewood cell wall thickness. The extra irrigation in September did not produce noticeable differences in xylogenesis compared to trees in the control treatment. The synchronization of maximum cambial division rates around the vernal equinox (spring) could allow Mediterranean trees to mitigate the impact of summer drought. With the predicted increase in drought intensity and frequency, lower tree productivity, carbon sequestration, and wood biomass are expected.

Changes in Some Mechanical and Physical Properties and Anatomical Structure of Spruce and Larch Wood after Fire-Retardant Treatment

Changes in the physical and mechanical properties and anatomical structures of spruce (Picea) and larch (Larix) specimens before and after fire-retardant impregnation were studied. Results indicated that the static modulus of elasticity (MOE), dynamic modulus of elasticity (DMOE), and the Brinell hardness of the specimens decreased for both wood species upon post-treatment. This could be accounted for by the degradation of hemicelluloses by the phosphorus-based compound, the minute cracks in the latewood cell wall, and the enlarged width of the cell lumen of the specimen resulting from the vacuum-pressure treatment. However, the decreased ratio of the MOR and DMOE to density contributed to lower sound transmission, which is expected to be important in a housing environment.

A 277 year cool season dam inflow reconstruction for Tasmania, southeastern Australia

AbstractSeasonal variability is a significant source of uncertainty in projected changes to precipitation across southeastern Australia (SEA). While existing instrumental records provide seasonal data for recent decades, most proxy records (e.g., tree rings, corals, speleothems) offer only annual reconstructions of hydroclimate. We present the first cool‐season (July–August) reconstruction of dam inflow (Lake Burbury) for western Tasmania in SEA based on tree‐ring width (Athrotaxis selaginoides) and mean latewood cell wall thickness (Phyllocladus aspleniifolius) chronologies. The reconstruction, produced using principal component regression, verifies back to 1731 and is moderately skillful, explaining around 23% of the variance. According to the reconstruction, relatively low inflow periods occurred around 1860, the early 1900s and 1970, while relatively high inflows occurred in the 1770s and 1810s. Highest reconstructed inflows occurred in 1816, and lowest in 1909. Comparison with available documentary and instrumental records indicates that the reconstruction better captures high rather than low flow events. There is virtually no correlation between our reconstruction and another for December–January inflow for the same catchment, a result consistent with the relationship between seasonal instrumental data. This suggests that conditions in one season have not generally reflected conditions in the other season over the instrumental record, or for the past 277 years. This illustrates the value of obtaining reconstructions of regional hydroclimatic variability for multiple individual seasons in regions where dry and wet seasons are not strongly defined. The results also indicate that the hydroclimate of the southeastern Australian region cannot be adequately represented by a single regional reconstruction.

Facilitating tree-ring dating of historic conifer timbers using Blue Intensity

Dendroarchaeology almost exclusively uses ring-width (RW) data for dating historical structures and artefacts. Such data can be used to date tree-ring sequences when regional climate dominates RW variability. However, the signal in RW data can be obscured due to site specific ecological influences (natural and anthropogenic) that impact crossdating success. In this paper, using data from Scotland, we introduce a novel tree-ring parameter (Blue Intensity – BI) and explore its utility for facilitating dendro-historical dating of conifer samples. BI is similar to latewood density as they both reflect the combined hemicellulose, cellulose and lignin content in the latewood cell walls of conifer species and the amount of these compounds is strongly controlled, at least for trees growing in temperature limited locations, by late summer temperatures. BI not only expresses a strong climate signal, but is also less impacted by site specific ecological influences. It can be concurrently produced with RW data from images of finely sanded conifer samples but at a significantly reduced cost compared to traditional latewood density. Our study shows that the probability of successfully crossdating historical samples is greatly increased using BI compared to RW. Furthermore, due to the large spatial extent of the summer temperature signal expressed by such data, a sparse multi-species conifer network of long BI chronologies across Europe could be used to date and loosely provenance imported material.

Characterizing phenol–formaldehyde adhesive cure chemistry within the wood cell wall

Adhesive bonding of wood using phenol–formaldehyde remains the industrial standard in wood product bond durability. Not only does this adhesive infiltrate the cell wall, it also is believed to form primary bonds with wood cell wall polymers, particularly guaiacyl lignin. However, the mechanism by which phenol–formaldehyde adhesive integrally interacts and bonds to lignin within the cell wall remains unclear. We used recently developed solubilization methodologies in conjunction with two-dimensional 1H–13C solution-state NMR spectroscopy of ball-milled pine earlywood and latewood bonded assemblies to characterize the chemical modification of wood cell wall polymers after phenol–formaldehyde curing at various cooking times. The results showed that the highly alkaline resin at 140°C decreased the frequency of the principal arylglycerol-β-aryl ether interunit linkage by eighty percent in earlywood and by twenty percent in latewood. The presence of newly formed diarylmethanes between guaiacyl lignin units and phenolic methylols was confirmed via NMR spectra of the aliphatic methylene and aromatic regions. The phenol–formaldehyde cure chemistry showed that o–p methylene bridges dominated in both earlywood and latewood cell walls, but the propensity of p–p substitution is higher in the latewood cell wall. Our results provide evidence for a simultaneous wood polymer degradation and guaiacyl unit C5 bond formation that occurs during phenol–formaldehyde curing. This competition may be necessary for developing good bond durability between the adhesive and wood.

Influence of climatic factors on tree-ring maximum latewood density of Picea schrenkiana in Xinjiang, China

The influence of temperature and precipitation on maximum latewood density (MXD) was mainly discussed in this paper, based on the samples of Picea schrenkiana from the Manas River Basin, Xinjiang, China. The correlation analysis between MXD and instrumental records from the Shihezi Meteorological Station showed that the MXD was positively related to the mean maximum temperature throughout the growing season at high elevations. Comparatively, the ring-width at low altitudes was limited by the precipitation in May-June. The composite chronology by MXD sequences was highly correlated with the mean maximum temperature in July-August (r = 0.54, p 2.5) in the period of 1953-2008 A.D. or close to 1.5σ for 2-3 consecutive years. The response characteristics are linked with the semiarid climate in the study area. In a single year or consecutive years of extreme dryness, the lack of precipitation would limit the thickening of latewood cell walls and thus impact the MXD. All in all, if a MXD chronology is aimed to reconstruct temperature history, the moisture conditions at the sampling site should be considered prudently.

Hygroscopic swelling and shrinkage of latewood cell wall micropillars reveal ultrastructural anisotropy

We document the hygroscopic swelling and shrinkage of the central and the thickest secondary cell wall layer of wood (named S2) in response to changes in environmental humidity using synchrotron radiation-based phase contrast X-ray tomographic nanoscopy. The S2 layer is a natural fibre-reinforced nano-composite polymer and is strongly reactive to water. Using focused ion beam, micropillars with a cross section of few micrometres are fabricated from the S2 layer of the latewood cell walls of Norway spruce softwood. The thin neighbouring cell wall layers are removed to prevent hindering or restraining of moisture-induced deformation during swelling or shrinkage. The proposed experiment intended to get further insights into the microscopic origin of the anisotropic hygro-expansion of wood. It is found that the swelling/shrinkage strains are highly anisotropic in the transverse plane of the cell wall, larger in the normal than in the direction parallel to the cell wall's thickness. This ultrastructural anisotropy may be due to the concentric lamellation of the cellulose microfibrils as the role of the cellulose microfibril angle in the transverse swelling anisotropy is negligible. The volumetric swelling of the cell wall material is found to be substantially larger than the one of wood tissues within the growth ring and wood samples made of several growth rings. The hierarchical configuration in wood optimally increases its dimensional stability in response to a humid environment with higher scales of complexity.

Comparison of Dilute Acid and Sulfite Pretreatment for Enzymatic Saccharification of Earlywood and Latewood of Douglas fir

This study applied dilute acid (DA) and sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) to deconstruct earlywood and latewood cell walls of Douglas fir for fermentable sugars production through subsequent enzymatic hydrolysis. DA pretreatment removed almost all the hemicelluloses, while SPORL at initial pH = 4.5 (SP-B) removed significant amount of lignin between 20 and 25 %. But both are not sufficient for effective enzymatic saccharification. SPORL at low initial pH = 2 (SP-AB) combines the advantage of both DA and SPORL-B to achieve approximately 90 % hemicellulose removal and delignification of 10–20 %. As a result, SP-AB effectively removed recalcitrance and thereby significantly improved enzymatic saccharification compared with DA and SP-B. Results also showed that earlywood with significantly lower density produced less saccharification after DA pretreatment, suggesting that wood density does not contribute to recalcitrance. The thick cell wall of latewood did not limit chemical penetration in pretreatments. The high lignin content of earlywood limited the effectiveness of DA pretreatment for enzymatic saccharification, while hemicellulose limits the effectiveness of high pH pretreatment of SP-B. The higher hemicellulose content in the earlywood and latewood of heartwood reduced saccharification relative to the corresponding earlywood and latewood in the sapwood using DA and SP-AB.

Relationship between Anatomical and Mechanical Properties of Loblolly Pine (Pinus taeda)

ABSTRACT The goal of this study was to investigate the effects of thinning and fertilization on mechanical properties of loblolly pine (Pinus taeda L.) strands associated with growth ring number and height. A systematic link to forest management, anatomical properties, and mechanical properties was obtained by correlating the test results with anatomical properties. The modulus of elasticity (MOE) and ultimate tensile strength (UTS) of strands from three loblolly pine trees increased with the increment in growth ring number, whereas the MOE and UTS showed different trends with the increment in height. Prediction of the MOE and UTS with specific gravity for the trees seemed to be unreliable. A natural tree had the greatest correlation between tangential latewood cell wall thickness and the mechanical properties. A thinned tree had the greatest correlation between ring width and the mechanical properties. A fertilized tree had the greatest correlation between density and the mechanical properties. However, the correlation between a specific anatomical property and mechanical properties was weak. Different combinations of anatomical properties predicted MOE and UTS of loblolly pine strands from different forest-managed trees more closely, indicating an R2 of 0.84 to 0.95.

Micromechanics and ultrastructure of pyrolysed softwood cell walls

Pyrolytic conversion causes severe changes in the microstructure of the wood cell wall. Pine wood pyrolysed up to 325 °C was investigated by transmission electron microscopy, atomic force microscopy and nanoindentation measurements to monitor changes in structure and mechanical properties. Latewood cell walls were tested in the axial, radial and tangential directions at different temperatures of pyrolysis. A strong anisotropy of elastic properties in the native cell wall was found. Loss of the hierarchical structure of the cell wall due to pyrolysis resulted in elastic isotropy at 300 °C. The development of the mechanical properties with increasing temperature can be explained by alterations in the structure and it was found that the elastic properties were clearly related to length and orientation of the microfibrils.

Light rings in Chinese pine (Pinus tabulaeformis) in semiarid areas of north China and their palaeo‐climatological potential

Light rings in conifer trees are characterized by a light-coloured, narrow latewood band of thin-walled tracheids. Most reports on light rings have been for subarctic and subalpine regions, and little is known about their occurrence in semiarid areas. Dendrochronological methods were used to date the occurrence of light rings in Chinese pine (Pinus tabulaeformis) in the semiarid region of north China. The anatomical and chemical characteristics and the potential environmental controls of their formation were investigated. Light rings in Chinese pine were dated to the year of their formation. The wall thickness and lumen diameter of the wood cells of light rings and reference rings were distinctly different. However, the configuration of the light-ring latewood cell walls was normal, although they were thinner than average, and their lignification had been completed normally. The climate characteristics that result in light-ring formation appear to be ongoing severe drought from the previous autumn to July of the current year in conjunction with a warm summer, suggesting that light rings can be used as indicators for past drought events.

The Relationship Between Variability of Cell Wall Mass of Earlywood and Latewood Tracheids in Larch Tree-Rings, the Rate of Tree-Ring Growth and Climatic Changes

Summary Mass accumulation dynamics in earlywood and latewood cell walls of larch from northern regions of Central Siberia are investigated and correlations among cell mass of different tree-ring zones, radial tracheid sizes and tree-ring width are found. A linear relationship exists between cell wall mass and radial cell size. The deviation of cell mass from the regression line (index of mass deviation) and the mean density of the respective tree-ring zone are similarly functionally dependent on the radial cell size and reflect the realization of the potential determined during the period of cell formation. There is a critical value of larch tree-ring width in relation to cell mass. For the tree-rings with width less than this critical value the difference in the mass of earlywood and latewood cells increases with decreasing tree-ring width.The cell wall mass correlates with the monthly temperatures of June and July. Under favorable growing conditions tracheids with similar mass of cell walls are formed in earlywood and latewood, while under unfavorable conditions cell wall mass accumulation in latewood is severly limited. A comparative analysis of the cell wall mass in earlywood and latewood indicates that mass accumulation is independent of the switching processes from earlywood production to the production of latewood.

A Quantitative Definition of Light Rings in Black Spruce (Picea mariana) at the Arctic Treeline in Northern Québec, Canada

Light rings in black spruce (Picea mariana [Mill.] BSP.) at the arctic treeline are characterized by pale-colored latewood made of a single or very few latewood-cell layers with thin-walled cells. Their widespread occurrence and their high frequency greatly facilitate the cross-dating procedure in dendrochronological studies. In this study, black spruce tree-ring density and wood structure were analyzed for light ring characteristics along with the mechanism of their formation according to ambient temperature. Light rings were quantitatively categorized into three classes based on the maximum tree-ring density using a normalized standard distribution. A light-ring chronology was established according to this classification. The results indicate that the grade of light ring was positively related to the frequency of light rings obtained from visual light-ring chronologies. The following anatomic variables were examined: number of cell layers of latewood, number of cells of the whole ring, percentage of latewood in the total ring width, and mean latewood cell-wall thickness. Among these anatomic variables, the mean latewood cell-wall thickness represents the best quantitative descriptor of a typical light ring as recognized by optical examination. The main causal factors of light rings are insufficient length of the growing season or cool summers.