Latewood Cells Research Articles

Gluing parameters optimization and failure mechanism of cross-laminated timber prepared with Chinese fir

Cross-laminated timber (CLT) has become a popular engineered wood product, mainly prepared from imported wood in China. More extensive research is needed to improve the local production of cross-laminated timber with fast-growing coniferous wood species. Chinese fir (Cunninghamia lanceolata) and one component polyurethane (1C-PUR) adhesive were selected to prepare CLT under different process parameters. International standard methods, scanning electron microscopy (SEM), optical microscopy (LM), confocal laser scanning microscopy (CLSM), and nanoindentation (NI) were applied. The bonding performance and failure mechanism of Chinese fir CLT were investigated and clarified. The results showed that the optimal gluing parameters for preparing CLT from Chinese fir wood were 160 g/m2 of glue, 0.9 MPa of pressure, and 180 minutes of pressing time. Failure of CLT made from Chinese fir lumber was mainly due to the shear failure of the vertical layer board. Cracks often appeared in the earlywood cells near the boundary between earlywood and latewood. The impact of adhesive penetration on the mechanical properties of the wood cell wall showed that adhesive penetration increased the elastic modulus of the cell wall at earlywood and latewood cells.

Stress distribution and microstructural response of radiata pine under high-intensity microwave (HIMW) treatment

ABSTRACT In this study, the stress distribution within the cell wall layers and the microstructural response under high-intensity microwave (HIMW) treatment were investigated. Finite-element models were developed for both single tracheid and multicellular structures, considering the influence of the saturated vapour pressure. The findings showed uniform vapour pressure caused expansion and deformation of the tracheid layers, with the radial wall deforming slightly more than the tangential wall due to differences in microfibril angle (MFA) and elastic properties. Despite its thinness, the S3 layer, with a wide MFA, played a pivotal role in supporting the saturated vapour pressure within the cell lumen under HIMW treatment, effectively constraining lateral cell-wall deformation. In contrast, the S2 layer, being the thickest, exhibited lower lateral elasticity and sustained damage at the interfaces with the S3 and S1 layers during the expansion and recovery stages. The multicellular simulation demonstrated that earlywood cells experienced larger deformations than latewood cells and revealed a negative correlation between the cell-wall thickness and deformation. The simulation results were validated through the microscopic analysis of the wood topography after HIMW treatment. The findings of this study provide significant insights into understanding the microstructural deformation of wood under HIMW treatment.

Intra-annual dynamic of opposite and compression wood formation of Pinus massoniana Lamb. in humid subtropical China

Radial growth of trees can result in opposite wood (OW) and compression wood (CW) due to the varying impact of stem mechanical stress, such as that caused by gravity or wind. Previous research has identified higher xylem production in CW compared to OW. Yet, it remains unclear whether the difference in the number of xylem cells between OW and CW results from differences in growth rate or the duration of xylem cells. In this study, we collected wood microcores on a weekly basis from March 2019 to January 2020 in Pinus massoniana Lamb. located on a steep slope. Our objective was to compare the dynamic of cambial activity and resulting cellular anatomical parameters between OW and CW in a humid subtropical environment. Our results showed that the xylem phenology of OW and CW was generally consistent with the xylem cell division process beginning in early March and ceasing in November. The last latewood cell completed its differentiation at the end of December. The response of wood formation dynamics to climate was consistent in both OW and CW. Moreover, both wood types exhibited a limited development of the enlargement phase due to the heat and drought during the summer. The rate of cell division was responsible for 90.7% of the variability in the number of xylem cells. The CW xylem obtained a larger number of cells by increasing the rate of cell division and displayed thinner earlywood cells with larger lumens than OW cells. Our findings showed that the xylem of conifer species responds to mechanical stress by accelerating the cell division rate. As a result, we suggest calculating the ratio between OW and CW widths to reconstruct wind stress changes rather than calculating the residuals used in the current study.

Properties of Catalpa bungei (Bignoniaceae) earlywood and latewood in the same growth ring during moisture adsorption/desorption: swelling and shrinkage at the cell level

Summary In this study, Dynamic Vapor Sorption Resolution combined with a Dino-Lite Edge Digital Microscope was used to document in real-time the swelling/shrinkage behavior of earlywood and latewood cells (wood fiber and vessel) on homogeneous samples of Catalpa bungei C.A.Mey. at the microscopic scale. The results showed that the lumen and cell wall of wood fibers swelled with the increase of relative humidity and shrank with the decrease of relative humidity in the sorption cycle of 0∼95% relative humidity condition. However, vessels showed an opposite trend to the behaviors mentioned above. In any region of both types of cells, latewood cell size (area and diameter) changed more significantly. For diameter change, the change of tangential diameter was larger than that of radial diameter. In addition, in the sorption cycle, the size (area and diameter) change of any region of wood fiber and vessel showed swelling hysteresis. Compared with earlywood cells, latewood cells had a more pronounced swelling hysteretic value, and the swelling hysteretic value in the tangential direction was higher than that in the radial direction in terms of diameter. Sorption hysteresis might be one of the contributing factors to swelling hysteresis. Finally, it was found that under any relative humidity, the dimensional changes of the wood fibers and the vessels were immediately stabilized when the moisture content reached its equilibrium.

Quasistatic and Dynamic Nanoindentation Measurements of Pinus radiata D. Don S2 and CCML Cell Wall Layers

Quasistatic nanoindentation is a proven tool that provides information on the micromechanical behavior of wood cell walls. However, quasistatic tests cannot probe the time-dependent mechanical behavior shown by wood. Nanoindentation dynamic mechanical analysis (nanoDMA) can measure the viscoelastic properties of wood cell walls. This research aimed to study the quasistatic and viscoelastic properties of individual radiata pine wood (Pinus radiata D. Don) cell wall layers. To minimize variability and retrieve both properties at the same locations, a load function composed of a multiload-quasistatic function followed by dynamic reference frequency segments was developed. Nanoindentations were then performed on the S2 layer and compound corner middle lamella (CCML) of unembedded latewood cells. Because the S2 layer is anisotropic, both transverse and longitudinal–tangential wood planes were studied. In the transverse plane, the average results of the quasistatic elastic moduli Es for the S2 layer and CCML were 15.7 GPa and 4.6 GPa, respectively. In the longitudinal–tangential plane, the Es was 3.9 GPa. In the transverse section, the hardness H of the S2 layer and CCML were 331 MPa and 277 MPa, respectively, and in the longitudinal–tangential section H was 244 MPa. To acquire the viscoelastic properties, measurements were made over more than three decades of frequency. An increase of the storage modulus E′, and a reduction of the loss modulus E″ and loss factor tanδ as frequency increased were found in both wood orientations. The quasi-static and dynamic indentations equivalent at 0.1 Hz showed similar values for Es and E′. This study contributes to our knowledge of wood cell wall micromechanical properties.

Mismatch between primary and secondary growth and its consequences on wood formation in Qinghai spruce.

The connections between the primary and secondary growth of trees allows better understanding of the dynamics of carbon sequestration in forest ecosystems. The relationship between primary and secondary growth of trees could change due to the diverging responses of meristems to climate warming. In this study, the bud phenology and radial growth dynamics of Qinghai spruce (Picea crassifolia) in arid and semi-arid areas of China in 2019 and 2020 were weekly monitored to analyze their response to different weather conditions and their links with carbon sink. Xylem anatomical traits (i.e. lumen radial diameter and cell wall thickness) were quantified along cell radial files after the end of xylem lignification to calculate the early-to-latewood transition date. Winter and early spring (January-March) were warmer in 2020 with a colder April compared with 2019. Precipitation in April-June was lower in 2020 than in 2019. In 2019, bud phenology occurred earlier, while the onset of xylem formation and the early-to-latewood transition date were delayed. The duration from the beginning of split bud and exposed shoot to the early-to-latewood transition date was positively correlated with the radial width of earlywood (accounting for ~80% of xylem width) and total xylem width. The longer duration of xylem cell division did not increase xylem cell production and radial width. Moreover, the duration from bud burst to the early-to-latewood transition date in 2020 was negatively linked with early phloem cell production as compared with 2019. Our findings suggest that warm conditions in winter and early spring promote the xylogenesis of Qinghai spruce, but might delay bud burst. However, the xylem width increments largely depend on the duration from bud burst to the start of latewood cell division rather than on the earlier xylogenesis and longer duration of xylem cell differentiation induced by warm conditions.

Effects of the Most Appropriate Proportion of Phytohormones on Tree-Ring Growth in Clones of Hybrid Larch

The increase in the atmospheric carbon dioxide concentration promotes its accumulation in trees by regulating the synthesis and transportation genes for endogenous hormones, such as IAA and GA, which are key factors in regulating various life activities, including growth rings. To explore the impact of changes in endogenous hormone levels such as IAA and GA on the growth of tree rings, and to provide a basis for improving the management of hybrid larch clonal forests, we investigated the effects of exogenous indole-3-acetic acid (IAA), gibberellic acid 3 (GA3), and their combination on tree-ring growth in hybrid larch. IAA, GA3, and a combination treatment were sprayed on the leaves of one clone of a hybrid larch seedling every three days. Small blocks were collected at the base stems for sequential anatomical observations. The phytohormone type, instead of the concentration, had a more significant effect on wood formation. Specifically, IAA treatment at 300 mg L−1 significantly increased latewood (LW) layers until 90 days after treatment (DAT). The 500 mg L−1 treatment significantly increased the wall radial thickness (WRT) of latewood (LW) cells. GA3 treatment at 100 mg L−1 significantly decreased the layers and width of total wood (TW), LW, and earlywood (EW). The 300 mg L−1 treatment significantly increased the WRT of EW. The IAA 100 mg L−1 + GA3 100 mg L−1 combination treatment significantly increased the layers and width of TW and LW by inducing cambium activity and increasing the rate of wood cell development. The WRT and lumen radial diameter (LRD) of EW or LW in this treatment were similar to those observed with the corresponding single phytohormone treatment. These results indicate that combination treatment at 100 mg L−1 + 100 mg L−1 was a better way to promote tree-ring growth. Our study suggests that changes in phytohormone levels and ratios are important factors that affect tree-ring formation. Hormone levels and ratios should be regarded as important indicators to guide the improvement of management practices in hybrid larch clonal plantations.

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.

Is the Pinus massoniana Lamb. Tree-Ring Latewood Formation Influenced by the Diurnal Temperature Range in Humid Subtropical China?

Tree-ring latewood is a key proxy for the reconstruction of climate, especially for temperature. The mechanisms of latewood formation and its responses to climates remain uncertain. Given that the tree-ring latewood of the taproot is absent belowground under conditions of low temperature gradients, we thus hypothesize that low diurnal temperature ranges (DTRs) may be one determining factor for latewood production. To evaluate this hypothesis, we designed experimental investigations by adding heat-protecting layers to the trunks of Pinus massoniana Lamb. to lower DTRs and simulate the environmental conditions underground in the Fuzhou area of humid subtropical China (HSC). We found that a decreased DTR induces a significant decline in latewood cell thickness and a slight reduction in latewood cell number and latewood density. DTRs played an important role in the formation of tree-ring width (TRW) and latewood width (LWW) rather than precipitation. Our study highlighted the effects of DTRs on tree growth and wood anatomical changes and provided a possible explanation for the “divergence problem” in dendroclimatology.

Cell characteristics of Larix principis-rupprechtii on the edge of different stand types

To analyze the effects of forest edge on radial growth and cell characteristics in different stand types of Larix principis-rupprechtii, we investigated the differences on radial growth, cell size and numbers between edge trees and inner trees of L. principis-rupprechtii in pure L. principis-rupprechtii forests and mixed forests of L. principis-rupprechtii and Betula platyphylla in Saihanba mechanical forest farm, China. The results showed that radial growth of the edge trees was significantly faster than that of the inner trees in pure forests, with the total ring width, earlywood width and latewood width of edge trees being 48.9%, 58.9% and 29.6% higher than those of inner trees, respectively. However, there was no difference in radial growth between edge trees and inner trees in mixed forest. The total number of earlywood cells, the number of large cells and small cells in earlywood of edge trees were increased by 63.3%, 55.6% and 70.0%, while the total number of latewood cells, the number of large cells and small cells in latewood of edge trees were increased by 35.4%, 37.5% and 28.5% compared with those of inner trees. There was no significant difference in the cell sizes between edge trees and inner trees. The cell numbers of earlywood and latewood of edge trees were not significantly different from those of inner trees in mixed forest, but the cell size in the earlywood of edge trees was 50.0% larger than those of inner trees in mixed forest. The sizes of the largest cells, the smallest cells, the large cells and the small cells in the earlywood of edge trees were increased by 28.6%, 33.3%, 16.6% and 25.0% compared with those of inner trees, respectively. The fast growth of edge trees and slow growth of inner trees in the pure forests could be effectively alleviated by cultivating mixed forests.

Quantitative prediction of moisture content distribution in acetylated wood using near-infrared hyperspectral imaging

The uptake of moisture severely affects the properties of wood in service applications. Even local moisture content variations may be critical, but such variations are typically not detected by traditional methods to quantify the moisture content of the wood. In this study, we used near-infrared hyperspectral imaging to predict the moisture distribution on wood surfaces at the macroscale. A broad range of wood moisture contents were generated by controlling the acetylation degree of wood and the relative humidity during sample conditioning. Near-infrared image spectra were then measured from the surfaces of the conditioned wood samples, and a principal component analysis was applied to separate the useful chemical information from the spectral data. Moreover, a partial least squares regression model was developed to predict moisture content on the wood surfaces. The results show that hyperspectral near-infrared image regression can accurately predict the variations in moisture content across wood surfaces. In addition to sample-to-sample variation in moisture content, our results also revealed differences in the moisture content between earlywood and latewood in acetylated wood. This was in line with our recent studies where we found that thin-walled earlywood cells are acetylated faster than the thicker latewood cells, which decreases the moisture uptake during the conditioning. Dynamic vapor sorption isotherms validated the differences in moisture content within earlywood and latewood cells. Overall, our results demonstrate the capabilities of hyperspectral imaging for process analytics in the modern wood industry.Graphical abstract

Origin of Intra-annual Density Fluctuations in a Semi-arid Area of Northwestern China.

Intra-annual density fluctuation (IADF) is a structural modification of the tree ring in response to fluctuations in the weather. The expected changes in monsoon flow would lead to heterogeneous moisture conditions during the growing season and increase the occurrence of IADF in trees of the arid ecosystems of continental Asia. To reveal the timings and physiological mechanisms behind IADF formation, we monitored cambial activity and wood formation in Chinese pine (Pinus tabuliformis) during 2017–2019 at three sites in semi-arid China. We compared the dynamics of xylem formation under a drought event, testing the hypothesis that drought affects the process of cell enlargement and thus induces the production of IADF. Wood microcores collected weekly from April to October were used for anatomical analyses to estimate the timings of cambial activity, and the phases of enlargement, wall thickening, and lignification of the xylem. The first cells started enlargement from late April to early May. The last latewood cells completed differentiation in mid-September. Trees produced IADF in 2018. During that year, a drought in June limited cell production in the cambium, only 36% of the xylem cells being formed in IADF trees, compared to 68% in normal tree rings. IADF cells enlarged under drought in early July and started wall thickening during the rainfall events of late July. The drought restricted cell enlargement and affected wall thickening, resulting in narrow cells with wide walls. Cambium and cell enlargement recovered from the abundant rainfall, producing a new layer with large earlywood tracheids. IADF is a specific adaptation of trees to cope with water deficit events occurring during xylem formation. Our findings confirmed the hypothesis that the June-July drought induces latewood-like IADFs by limiting the process of cell enlargement in the xylem. Our finding suggests a higher occurrence of IADF in trees of arid and semi-arid climates of continental Asia if the changes to monsoon flows result in more frequent drought events during the earlywood formation in June.

Reconstruction of gully erosion based on exposed tree roots in a recent landform of Paricutin Volcano, Mexico

AbstractGullies in volcanic deposits are among the first signs of erosion that can be observed during or immediately after the volcanic activity and reflective of unstable conditions of newly formed deposits. Gully formation and erosion pulses may well continue to occur long after the initial landform was created, mostly as a result of torrential rainfall and/or land‐use changes. Yet, proper understanding of erosion dynamics and its relations with environmental drivers remains challenging as long‐term observations are, especially in volcanic terrain. Here we applied dendrogeomorphic approaches to (i) analyse both microscopic and macroscopic disturbances in tree roots exposed by gully erosion in a young volcanic landform of central Mexico and to (ii) quantify the evolution of erosion in the volcanic deposits of Paricutin Volcano. To this end we analysed 154 cross‐sections of 30 living, exposed roots of Pinus pseudoestrobus Lindl., of which 25 were used for anatomical and 129 for macroscopic analysis. Wood anatomical – or microscopic – disturbances were mostly in the form of strong growth reductions (~50%) in lumen area of earlywood tracheids, substantial increases in ring widths (mostly stemming from eccentric growth) and the increased formation of latewood cells. We observe major erosion pulses in 2010, 2012, 2015, 2016, 2017 and 2018, triggered primarily by torrential rainfall (with >100 mm 24 h−1 for the maximum intensity event: standard precipitation index values ≥ 2). Along the gully, the lower sector formed between 2009 and 2017, whereas the central sector exhibited important phases of exposure from 2012 to 2018. In the upper, most recent sector of the gully, erosion started only in 2017. Erosion rates in the lower and upper sectors are smaller with a channel widening rate of 6 to 16 cm yr−1. Around the main knickpoint found in the central part of the gully, retreat rates are up to 60 cm yr−1 and gully incision is 30 cm yr−1. The methods applied in this research are novel and can be applied to other volcanic environments with intense gully erosion, so as to provide baseline data for land‐use and environmental management plans.

Effects of moisture and heat coupling on xylem growth of Pinus tabuliformis in Shenyang, China

Based on the micro-core technology, we can accurately examine the tree cambium phenology and the radial growth at the cellular scale, and reveal the relationship between tree growth and climate. Pinus tabuliformis is one of the constructive species in forests of northern China. We investigated the growth pattern of P. tabuliformis in Shenyang and the changes in cambium and xylem cells throughout the growing season (April to November) in 2020. Results showed that the dividing activity in cambium started in early April and ended at the end of September. Xylem began to grow from the appearance of enlargement cells (mid April) to the end of the disappearance of lignified cells (late October), with a growth trajectory of 'S' shape curve. Approximately 53 xylem cells per row in radical direction were produced in 2020. The maximum growth rate (0.55 ind/row/day) occurred at the end of May, while the change of earlywood and latewood cells occurred at the end of July. When the minimum temperature above 0 ℃ in Shenyang, the cambium began to divide. The minimum critical temperature that affected the beginning and ending of xylem growth was 2-3 ℃. Precipitation promoted the growth in the growing season. The high temperature and insufficient water supply at the end of July were the main factors driving the differentiation of xylem cells to form earlywood and latewood.

Triggering Bimodal Radial Stem Growth in Pinus sylvestris at a Drought-Prone Site by Manipulating Stem Carbon Availability.

A bimodal radial growth (RG) pattern, i.e., growth peaks in spring and autumn, was repeatedly found in trees in the Mediterranean regions, where summer drought causes reduction or cessation of cambial activity. In a dry inner Alpine valley of the Eastern Alps (Tyrol, Austria, 750 m asl), Pinus sylvestris shows unimodal RG with onset and cessation of cambial activity in early April and late June, respectively. A resumption of cambial activity after intense summer rainfall was not observed in this region. In a field experiment, we tested the hypothesis that early cessation of cambial activity at this drought-prone site is an adaptation to limited water availability leading to an early and irreversible switch of carbon (C) allocation to belowground. To accomplish this, the C status of young P. sylvestris trees was manipulated by physical blockage of phloem transport (girdling) 6 weeks after cessation of cambial cell division. Influence of manipulated C availability on RG was recorded by stem dendrometers, which were mounted above the girdling zone. In response to blockage of phloem flow, resumption of cambial activity was detected above girdling after about 2 weeks. Although the experimentally induced second growth surge lasted for the same period as in spring (c. 2 months), the increment was more than twice as large due to doubling of daily maximum RG rate. After girdling, wood anatomical traits above girdling no longer showed any significant differences between earlywood and latewood tracheids indicating pronounced effects of C availability on cell differentiation. Below girdling, no reactivation of cambial activity occurred, but cell wall thickness of last formed latewood cell was reduced due to lack of C supply after girdling. Intense RG resumption after girdling indicates that cessation of cambial activity can be reversed by manipulating C status of the stem. Hence, our girdling study yielded strong support for the hypothesis that belowground organs exert high C sink strengths on the drought-prone study site. Furthermore, this work highlights the need of in-depth experimental studies in order to understand the interactions between endogenous and exogenous factors on cambial activity and xylem cell differentiation more clearly.

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.

Contribution of Xylem Anatomy to Tree-Ring Width of Two Larch Species in Permafrost and Non-Permafrost Zones of Siberia

Plants exhibit morphological and anatomical adaptations to cope the environmental constraints of their habitat. How can mechanisms for adapting to contrasting environmental conditions change the patterns of tree rings formation? In this study, we explored differences in climatic conditions of permafrost and non-permafrost zones and assessed their influence on radial growth and wood traits of Larix gmelinii Rupr (Rupr) and Larix sibirica L., respectively. We quantified the contribution of xylem cell anatomy to the tree-ring width variability. Comparison of the anatomical tree-ring parameters over the period 1963–2011 was tested based on non-parametric Mann-Whitney U test. The generalized linear modeling shows the common dependence between TRW and the cell structure characteristics in contrasting environments, which can be defined as non-specific to external conditions. Thus, the relationship between the tree-ring width and the cell production in early- and latewood are assessed as linear, whereas the dependence between the radial cell size in early- and latewood and the tree-ring width becomes significantly non-linear for both habitats. Moreover, contribution of earlywood (EW) and latewood (LW) cells to the variation of TRW (in average 56.8% and 24.4% respectively) was significantly higher than the effect of cell diameters (3.3% (EW) and 17.4% (LW)) for the environments. The results show that different larch species from sites with diverging climatic conditions converge towards similar xylem cell structures and relationships between xylem production and cell traits. The work makes a link between climate and tree-ring structure, and promotes a better understanding the anatomical adaptation of larch species to local environment conditions.