Tracheid Walls Research Articles

Lignification Markers of the Tracheid Walls of Scots Pine (Pinus sylvestris (L.)) in Various Forms of Dead Bark

This study attempted to define the shaping of the quotient of fresh-needled twig mass and fresh conifer needle mass to the lignin content (MFT/LC) in the tracheid walls of the circumferential zone of trunks (MFN/LC) of pines with various forms of dead bark, which were called lignification markers. In the experiment, the researched trees had varying forms of dead bark, including ropy bark (G), scaly bark (L), and shell-type bark (M). The research material came from pine timber forests aged between 89 years to 91 years, located in Northern Poland. A tree tissue chemical analysis encompassed a zone of mature sapwood, i.e., the last ten annual growth rings of diameter increment located at the height of 1.30 m (diameter at breast height-DBH). The acquired results pointed to the fact that pines with dead bark in the ropy form possessed statistically higher values of the analyzed markers (MFT/LC and MFN/LC) than the trees with scaly and shell-type bark. The variances ascertained in the course of the experiments of both markers in the Scots pine (Pinus sylvestris (L.)) are possibly connected to the physiological, physical, and structural conditioning of water transportation, with mineral salts in the stem of the trees.

New research perspectives from a novel approach to quantify tracheid wall thickness.

The analysis of xylem cell anatomical features in dated tree rings provides insights into xylem functional responses and past growth conditions at intra-annual resolution. So far, special focus has been given to the lumen of the water-conducting cells, whereas the equally relevant cell wall thickness (CWT) has been less investigated due to methodological limitations. Here we present a novel approach to measure tracheid CWT in high-resolution images of wood cross-sections that is implemented within the specialized image-analysis tool 'ROXAS'. Compared with the traditional manual line measurements along a selection of few radial files, this novel image-analysis tool can: (i) measure CWT of all tracheids in a tree-ring cross-section, thus increasing the number of individual tracheid measurements by a factor of ~10-20; (ii) measure the tangential and radial walls separately; and (iii) laterally integrate the measurements in a customizable way from only the thinnest central part of the cell walls up to the thickest part of the tracheids at the corners. Cell wall thickness measurements performed with our novel approach and the traditional manual approach showed comparable accuracy for several image resolutions, with an optimal accuracy-efficiency balance at 100× magnification. The configurable settings intended to underscore different cell wall properties indeed changed the absolute levels and intra- and inter-annual patterns of CWT. This versatility, together with the high data production capacity, allows to tailor the measurements of CWT to the specific goal of each study, which opens new research perspectives, e.g., for investigating structure-function relationships, tree stress responses and carbon allocation patterns, and for reconstructing climate based on intra- and inter-annual variability of anatomical wood density.

Fungal decay in Permian Glossopteridalean stem and root wood from Antarctica

Evidence of fungal decay is frequently encountered in silicified wood. However, studies focusing on fossil fungal wood degradation remain rare. A characteristic pattern of degradation and decay symptoms congruent with present-day white pocket rot occur in Late Permian silicified glossopteridalean stem and root wood (Australoxylon sp.) from Skaar Ridge, Antarctica. Co-occurring with the decay symptoms are fungal hyphae with clamp connections. Hyphae usually progress through the pit apertures, but some may also penetrate tracheid walls. The individual wall layers in some of the infected tracheids are separated from each other, apparently forming appositions. Small, opaque bodies (? arthropod coprolites) occur in some of the decay pockets. The abundance of infected specimens among the silicified woods from Skaar Ridge suggests that white pocket rot fungi were important decomposers in late Paleozoic high-latitude forest ecosystems.

A new occurrence of silicified wood from the Early Cretaceous (Berriasian) Kagbeni Formation of north central Nepal

During recent fieldwork a second occurrence of silicified wood has been discovered from the Early Cretaceous Kagbeni Formation of north central Nepal. The wood exhibits anatomical features which are well in accordance with Araucarioxylon nepalense described from another locality in the Kagbeni Formation near Kagbeni in the Thakkhola Valley in central Nepal. It is a pycnoxylic wood with mostly uniseriate and rarely biseriate bordered pits on radial tracheid walls. According to recent taxonomic opinions this type of wood should not be treated as Araucarioxylon, but as Agathoxylon Hartig. Thus, we propose the name Agathoxylon nepalense comb. nov. for this type of wood. The sandstones of the Kagbeni Formation have been interpreted as delta–deposits, with a major flow direction from the south. This suggests that the wood originated from the northern margin of Gondwana (i.e. the Indian Plate).

Plant-arthropod and plant-fungus interactions in late Permian gymnospermous woods from the Bogda Mountains, Xinjiang, northwestern China

Several lines of evidence of plant-arthropod and plant-fungus interactions are documented from the Wuchiapingian Wutonggou low-order cycle (approximate equivalent to the Wutonggou Formation) in Tarlong valley, southern Bogda Mountains, Xinjiang Uygur Autonomous Region, northwestern China. Fossil wood, Septomedullopitys szei Wan, Yang et Wang, contains differentially-damaged areas. Spindle-shaped pockets in the fossil wood occurring in the secondary xylem are commonly free of organic remains. They are comparable in appearance to modern white-pocket rot caused by fungi. The tracheid walls around the decomposed areas are degraded from the middle lamellae to outer layers. Abundant branching and septate fungal hyphae in the decayed areas, ray parenchyma and tracheid lumina indicate that fungi are responsible for the wood decay. These fungi are partially regarded as basidiomycetes because of the occurrence of clamp connections. According to the characteristic damages they caused to the host, ascomycetes are also viable candidates of the fungi because large parts of hyphae are without certain clamp connections. The other damaged excavations are branched and maze-like borings and galleries, which are filled with abundant fungal hyphae, cellular debris and spheroidal to ovoidal, dark-colored coprolites, ranging from 26 to 128μm in diameter. The size, shape, and surface texture of these coprolites indicates that the coprolites are the feces of ancient oribatid mites. The fungal hyphae, coprolites, and degraded excavations in the pith of the late Permian wood suggest that wood-rotting and -boring were not limited to the xylem.

Fracture in Norway spruce wood treated with Physisporinus vitreus

Changes in the fracture behaviour of Norway spruce tonewood after fungal treatment were studied. Specimens were incubated for 6, 9 and 12 months with Physisporinus (P.) vitreus. Fracture tests were performed in a compact-tension fracture experiment set-up, and the results were compared with the morphological analysis of the degraded wood structure and transverse sections of the crack tip viewed under light and fluorescence microscopy. It was evident that both the failure load and critical stress intensity factors were reduced in wood after prolonged incubation periods. Weight losses were significantly higher in sapwood than in heartwood. With prolonged incubation periods, the frequency of unstable fracture and brittle behaviour of the wood increased. In untreated wood, cracks were initiated in the earlywood. The process involved both delamination of the cells within the middle lamellae and rupture of the cell walls, inducing a zigzag crack tip pattern. In fungally treated wood, cracks often commenced from the intersection between late- and earlywood, resulting in a straight tangential crack line. Micrographic images showed that P. vitreus was more active in the secondary walls of latewood tracheids. In this region of the wood, the cell walls were strongly degraded after 9–12 months of incubation, resulting in a reduction in tensile strength, even though the wood did not show strong features of decay at the macroscopic level.

Quantifying size-dependent developmental trajectories of commercial-relevant fibre attributes within maturing black spruce plantations employing hierarchical linear models

The primary objective of this study was to quantitatively describe size-dependent developmental trajectories of commercially-relevant fibre attributes within maturing black spruce (Picea marina (Mill.) B.S.P.) plantations employing hierarchical linear models. A stratified random sample design was deployed within 5 density-stressed semi-mature plantations to obtain transverse breast-height radial xylem sequences from 47 trees representing 5 basal area size classes (quintiles). The cumulative annual ring-area-weighted moving average proceeding from the pith to the ith cambial age was calculated for density, microfibril angle, modulus of elasticity, fibre coarseness, tracheid wall thickness, tracheid dimensions (radial and tangential diameters) and specific surface area. Hierarchical linear regression models were used to quantify size-dependent effects on these developmental trajectories: (1) at the first hierarchical level, compound exponential models were specified following the assessment of a set of candidate functional forms; and (2) given (1), at the second hierarchical level, linear model specifications under fixed and random error structures were used to account for potential size-dependent effects on the first-level parameter estimates. In order to ensure statistically valid inferences regarding size-dependence by employing radial sequences devoid of serial correlation, and provide an independent data set for evaluating the parameterized models in terms of goodness-of-fit, lack-of-fit and predictive ability, the data set consisting of 1566 observations per attribute was systematically stratified into parameterization and valuation subsets. The results revealed that the parameters of the Hoerl-based compound exponential model varied by tree-size indicating the presence of significant (p⩽0.05) size-dependence in fibre attribute developmental trajectories. Statistical measures of model performance and associated graphical analysis of the final specifications indicated that the models performed well in terms of accounting for a relatively large proportion of variation (61–88%), unbiasedness and predictive ability (e.g., temporal invariant patterns in absolute and relative prediction errors). These results and related inferences demonstrated the utility of quantifying size-dependent fibre developmental trajectories employing hierarchical linear models.

Tracheid cell-wall structures and locations of (1 → 4)-β-d-galactans and (1 → 3)-β-d-glucans in compression woods of radiata pine (Pinus radiata D. Don)

BackgroundCompression wood (CW) forms on the underside of tilted stems of coniferous gymnosperms and opposite wood (OW) on the upperside. The tracheid walls of these wood types differ structurally and chemically. Although much is known about the most severe form of CW, severe CW (SCW), mild CWs (MCWs), also occur, but less is known about them. In this study, tracheid wall structures and compositions of two grades of MCWs (1 and 2) and SCW were investigated and compared with OW in slightly tilted radiata pine (Pinus radiata) stems.ResultsThe four wood types were identified by the distribution of lignin in their tracheid walls. Only the tracheid walls of OW and MCW1 had a S3 layer and this was thin in MCW1. The tracheid walls of only SCW had a S2 layer with helical cavities in the inner region (S2i). Using immunomicroscopy, (1 → 4)-β-D-galactans and (1 → 3)-β-D-glucans were detected in the tracheid walls of all CWs, but in only trace amounts in OW. The (1 → 4)-β-D-galactans were located in the outer region of the S2 layer, whereas the (1 → 3)-β-D-glucans were in the inner S2i region. The areas and intensities of labelling increased with CW severity. The antibody for (1 → 4)-β-D-galactans was also used to identify the locations and relative amounts of these galactans in whole stem cross sections based on the formation of an insoluble dye. Areas containing the four wood types were clearly differentiated depending on colour intensity. The neutral monosaccharide compositions of the non-cellulosic polysaccharides of these wood types were determined on small, well defined discs, and showed the proportion of galactose was higher for CWs and increased with severity.ConclusionThe presence of an S3 wall layer is a marker for very MCW and the presence of helical cavities in the S2 wall layer for SCW. The occurrence and proportions of (1 → 4)-β-D-galactans and (1 → 3)-β-D-glucans can be used as markers for CW and its severity. The proportions of galactose were consistent with the labelling results for (1 → 4)-β-D-galactans.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0884-3) contains supplementary material, which is available to authorized users.

Influencia climática sobre la variación radial de caracteres anatómicos de madera en Abies religiosa

Se caracterizó la variación radial de las dimensiones de las traqueidas y la identificación de las variables climáticas que influyen sobre la variación de las mismas en Abies religiosa (H.B.K.) Schldtl. & Cham. Se eligieron 20 árboles en una población de la sierra El Campanario, Michoacán. Las muestras fueron tomadas a la altura del pecho (1.30 m), y procesadas con microtecnia convencional para madera. Se analizaron cuatro características de las traqueidas y el ancho de los anillos de crecimiento en sentido radial. Los diámetros tangenciales de la traqueida y del lumen de la traqueida en la madera tardía, así como del lumen de la traqueida en la madera temprana, presentan un ligero incremento que va de la médula al cámbium vascular. El grosor de la pared de la traqueida en la madera tardía muestra un rápido incremento en la región cercana a la médula y posterior a este incremento, manifiesta amplias fluctuaciones. El ancho de los anillos de crecimiento tiene un patrón inverso al grosor de la pared. Los análisis de regresión mostraron que las temperaturas máximas afectan la acumulación y las características de las traqueidas. Los resultados sugieren que la actividad del cámbium vascular de Abies religiosa está relacionada con las temperaturas máximas.

First record of Podocarpoid fossil wood in South China

A new species of fossil conifer wood, Podocarpoxylon donghuaiense sp. nov., is described from the late Eocene of Nadu Formation in Baise Basin of the Guangxi Province, South China. This fossil wood is characterized by distinct growth rings, circular to oval tracheids in cross section, 1–2-seriate opposite pits on radial tracheid walls, uniseriate (rarely biseriate) rays, smooth end walls of ray parenchyma cells, and the absence of resin ducts, suggesting its affinity to Podocarpaceae. The new species is distinctive from other Cenozoic woods ascribed to this family by the combination of distinctive growth rings, the absence of axial parenchyma, the occurrence of bordered pits on tangential tracheid walls, and the occurrence of 3–4 cuppressoid or taxodioid pits on cross-fields. This represents the first record of podocarpoid fossil wood in South China and provides fossil evidence for the early dispersal and diversification of Podocarpaceae in eastern Asia as well as for mild temperate seasonal climate in this region during the late Eocene.

Responses of ray parenchyma cells to wounding differ between earlywood and latewood in the sapwood of Cryptomeria japonica

Changes in cellular contents of ray parenchyma cells during the formation of reaction zone differ between earlywood and latewood in the sapwood of Cryptomeria japonica. Changes over time in the cellular contents of xylem parenchyma cells provide important clues to the mechanism of the early events in the wound reaction of trees. In this study, we monitored the events that occur during the death of ray parenchyma cells after wounding. We examined nuclei, starch grains, and colored substances in ray parenchyma cells by light microscopy and the autofluorescence of cell walls of tracheids by confocal laser-scanning microscopy in Cryptomeria japonica after artificial wounding. In addition, we compared cytological changes in ray parenchyma cells in the longitudinal and radial directions. Finally, we analyzed the differences between earlywood and latewood in terms of the responses of ray parenchyma cells to wounding. Behind the wound, changes in cellular contents were visible first in latewood regions in the second annual ring behind the wound. The progression of changes in cellular contents of ray parenchyma cells stopped near the growth-ring boundary. These results indicate that the growth-ring boundary might prevent the spread of some factor(s) that induces cytological changes in ray parenchyma cells. Above the wound, most colored substances were localized in ray parenchyma cells that were located near wounds in latewood regions. Thus, even at an equal distance from the wound, the amount of secondary metabolites in ray parenchyma cells differed between earlywood and latewood. Our observations suggest that differences in the anatomical features of neighboring tracheids between earlywood and latewood might influence changes in cellular contents of ray parenchyma cells during reactions to wounding in Cryptomeria japonica.

Lignified woods of Pinus (Pinaceae) from the late Miocene of central Yunnan, China, and their biogeographic and paleoclimatic implications

Two new species, Pinus uniseriata and P. nanfengensis, were described on the basis of lignified fossil woods from the late Miocene of the Xianfeng Basin (central Yunnan, southwestern China). The woods of both species are characterized by gradual transition from early wood to late wood, predominantly uniseriate pitting in the tracheid walls, the absence of axial parenchyma and traumatic resin canals, the presence of axial and radial resin ducts, uniseriate rays, smooth to slightly pitted ray tracheids and pinoid/taxodioid pits in cross-field pits. They differ in that P. uniseriata wood has unisetiate marginal ray tracheids and taxodioid (occasionally cupressoid) pits whereas P. nanfengensis wood has ray tracheids usually arranged as biseriate, as well as pinoid and taxodioid cross-field pits. The fossil woods showed a considerable anatomical similarity to extant species P. bungeana and P. roxburghii, respectively, which are now absent from central Yunnan. Pinus uniseriata is the first macrofossil record for subsection Gerardianae. Pinus nanfengensis is the first fossil record of the subsection Pinaster outside Europe.

IDENTIFICATION AND CHARACTERISATION OF DOUGLAS-FIR (PSEUDOTSUGA MENZIESII (MIRB.) FRANCO) JUVENILE AND ADULT WOOD GROWN IN SOUTHERN GERMANY

More than one-third of Germany s Douglas-fir resources, stock in age-classes from twenty-one to fifty-nine years. As such timber increasingly enters markets, detailed knowledge of the anatomy and properties of its wood is of importance to forest managers and wood processors. Anatomical and mechanical wood analyses in this study were carried out on twenty trees from four scientifically managed plantations in Southern Germany. The age of the trees selected was forty-two years whereby varying growth conditions were considered. Juvenile and adult woods were identified by segmented linear regression of radial profiles of anatomical characteristics, such as latewood percentage, tracheid wall thickness microfibril angle and density. Additionally, the width of earlywood, latewood and growth rings as well as bending modulus of elasticity were determined. Variance was dependent on the trait used for differentiation, j uvenile wood comprised of an eleven to thirty-one growth rings resp. radial amounts of fifteen to sixty-five percent. When compared to adult wood, juvenile wood showed corresponding features of approximately thirty percent wider growth rings, th irty four percent lower latewood percentage, fourteen percent thinner tracheid walls, and eighty percent larger microfibril angles, eleven percent lighter wood and fifty -seven percent lower bending modulus of elasticity. As the assortment features fast grown trees, adult heartwood characteristics were slightly inferior to the characteristics of European Douglas-fir.

Improving the permeability of Douglas-fir (Pseudotsuga menziesii) containing compression wood by Physisporinus vitreus and Xylaria longipes

The bioincising impact of Physisporinus vitreus and Xylaria longipes on the porous structure, and permeability of Douglas-fir containing compression wood was investigated. Fungal cultivation was carried out at 25°C and 85% relative humidity in an incubator for three time periods, namely, 15, 30 and 45 days. Safranin solution was injected into wood specimens to evaluate liquid permeability whereas air permeability was measured by the falling-water method. Wood exposure to both fungi enhanced permeability by increasing incubation period. However, the parallel compression strength of wood reduced. Microscopic imagery revealed degradation of bordered pits, bore-hole formation through tracheid walls as well as ray damage which are thought to be main reasons for improvements in air and liquid permeability. No pronounced differences were found between the fungi in their effects on permeability. Parenchyma rays were also shown to play an important role in the radial permeability of Douglas-fir compression wood.

New record of fossil wood Xenoxylon from the Late Triassic in the Sichuan Basin, southern China and its paleoclimatic implications

Fossil wood is one of the significant proxies for terrestrial paleoclimate and paleogeographical reconstruction in Earth history. Abundant and diversified Mesozoic fossil woods are well recorded in China; however, Triassic fossil wood is very scarce. Here, we report a new fossil wood from the Late Triassic Xujiahe Formation (Norian to Rhaetian) in Guangyuan of northern Sichuan Basin, southwestern China. The fossil wood material consists of two well-preserved specimens yielding secondary xylem with distinct growth rings. Bordered pits on the radial tracheid walls are mostly contiguous, biseriate alternate, locally uniseriate and strongly flattened. Cross-fields show a large window-like pore. This anatomy is typical for the important fossil wood morphogenus Xenoxylon Gothan, and, based on a novel combination of radial and cross-field pitting type and ray height, a new species, Xenoxylon guangyuanense sp. nov. is recognized. The finding of this new fossil wood taxon contributes to a better understanding of the yet poorly documented Xenoxylon early radiation during the Late Triassic, as well as of the origin of X. meisteri group, a peculiar endemic group which diversified in Far-East Asia from the Triassic to the Early Cretaceous. Xenoxylon is a paleobiogeographically significant genus, being bound to cooler and/or wetter climates of Northern Hemisphere throughout its Late Triassic–Late Cretaceous range. The occurrence of Xenoxylon in the Sichuan Basin of southern China may indicate a short-term cooling event, sandwiched within a period during which warm and wet climate conditions largely prevailed over lower latitude regions of the Northern Hemisphere. Such a cooling event in the Sichuan Basin which was located at a low paleolatitude on the eastern rim of Tethys may be in accordance in time with the temperature decline event in Norian–Rhaetian boundary uncovered by oxygen isotope (δ18O) record in Italy of the western rim of Tethys.

In situ detection of laccase activity and immunolocalisation of a compression-wood-specific laccase (CoLac1) in differentiating xylem of Chamaecyparis obtusa.

The secondary cell wall of compression wood tracheids has a highly lignified region (S2L) in its outermost portion. To better understand the mechanism of S2L formation, we focussed on the activity of laccase (a monolignol oxidase) and performed in situ studies of this enzyme in differentiating compression wood. Staining of differentiating compression wood demonstrated that laccase activity began in all cell wall layers before the onset of lignification. We detected no activity of peroxidase (another monolignol oxidase) in any cell wall layer. Thus, laccase likely plays the major role in monolignol oxidisation during compression wood differentiation. Laccase activity was higher in the S2L region than in other secondary wall regions, suggesting that this enzyme was responsible for the high lignin concentration in this region of the cell wall. Immunolabelling demonstrated the expression of a compression-wood-specific laccase (CoLac1) immediately following the onset of secondary wall thickening, this enzyme was localised to the S2L region, whereas much less abundant in the S1 layer or inner S2 layer. Thus, the CoLac1 protein is most likely localised to the outer part of S2 and responsible for the high lignin concentration in the S2L region.

Localized cooling of stems induces latewood formation and cambial dormancy during seasons of active cambium in conifers

In temperate regions, trees undergo annual cycles of cambial growth, with periods of cambial activity and dormancy. Environmental factors might regulate the cambial growth, as well as the development of cambial derivatives. We investigated the effects of low temperature by localized cooling on cambial activity and latewood formation in two conifers, Chamaecyparis obtusa and Cryptomeria japonica. A plastic rubber tube that contained cooled water was wrapped around a 30-cm-wide portion of the main stem of Chamaecyparis obtusa and Cryptomeria japonica trees during seasons of active cambium. Small blocks were collected from both cooled and non-cooled control portions of the stems for sequential observations of cambial activity and for anatomical measurements of cell morphology by light microscopy and image analysis. The effect of localized cooling was first observed on differentiating tracheids. Tracheids narrow in diameter and with significantly decreased cambial activity were evident 5 weeks after the start of cooling in these stems. Eight weeks after the start of cooling, tracheids with clearly diminished diameters and thickened cell walls were observed in these stems. Thus, localized low temperature induced narrow diameters and obvious thickening of secondary cell walls of tracheids, which were identified as latewood tracheids. Two months after the cessation of cooling, a false annual ring was observed and cambium became active again and produced new tracheids. In Cryptomeria japonica, cambial activity ceased earlier in locally cooled portions of stems than in non-cooled stems, indicating that the cambium had entered dormancy sooner in the cooled stems. Artificial cooling of stems induced latewood formation and cessation of cambial activity, indicating that cambium and its derivatives can respond directly to changes in temperature. A decrease in the temperature of the stem is a critical factor in the control of cambial activity and xylem differentiation in trees.

A New Species ofTsuga(Pinaceae) based on Lignified Wood from the Late Miocene of Central Yunnan, China, and Its Paleoenvironmental Implications

AbstractA new species,Tsuga nanfengensissp. nov. (Pinaceae), is described on the basis of lignified fossil wood from the late Miocene of the Xianfeng Basin, central Yunnan, southwestern China. Detailed observation of the fossil wood specimens show the following characteristics: distinct growth rings, absence of resin canals, uniseriate bordered pits in the radial wall of tracheids, ray tracheids and piceoid and cupressoid cross‐field pits. These features indicate similarities to the wood of extantTsuga canadensis, T. chinensis, andT. dumosa. According to the fossil record,Tsugawas present in Xundian County during the Miocene. TodayTsugais drought intolerant, preferring wet conditions with no extant species growing naturally in Xundian County. The presence ofTsugain the Miocene of Xundian County indicates a humid climate consistent with previous palaeoclimatic reconstructions showing a wetter and probably shorter dry season in the Miocene, relative to the present day. Therefore, the change in the local climate such as increasing aridity through the Miocene might explain the local extinction ofTsugafrom central Yunnan.

A model of stem growth and wood formation in Pinus radiata

A model of wood formation processes in pines predicted 80 % of mean wood density variation from inputs of carbohydrate allocation and tree water status from several varied sites. Numerous factors determine how wood properties vary as a tree grows. In order to model wood formation, a framework that considers the various xylogenetic processes is required. We describe a new model of xylem development and wood formation in pines (parameterised for the commercially important species, Pinus radiata D. Don). In this paper, we use as inputs simulated daily data from the CaBala stand growth model which, in turn, takes into account site and daily weather conditions, and silviculture. It incorporates a first attempt at predicting microfibril angle (the angle of cellulose microfibrils relative to the vertical axis of the cell, MFA) based on metrics of cambial vigour and carbohydrate allocation. It also predicts tracheid dimensions and wall thickness, and from these data, wood density. Pith-to-bark and intra-annual variation in predicted wood properties was realistic across a wide range of site types, although juvenile wood properties were weakly predicted. The model was able to explain 50 % of the variation in outerwood MFA and 70–80 % of the variation in outerwood and mean sample wood density respectively, from 17 study sites. The model, early results from which are very promising, provides a useful framework for testing concepts of how formation occurs, and to provide insights into areas where further research is needed.

Wood decay of Xenoxylon yunnanensis Feng sp. nov. from the Middle Jurassic of Yunnan Province, China

Abstract A permineralised gymnosperm wood, Xenoxylon yunnanensis Feng sp. nov., is described from the Middle Jurassic Shaximiao Formation in Huize County, Yunnan Province, Southwest China. The pycnoxylic wood consists of thick-walled tracheids and thin-walled rays. It is characterised by uniseriate, contiguous, compressed bordered pits on the radial walls of tracheids, and one large simple pit in each cross-field. Growth rings exhibit narrow latewood. The mean sensitivity of analysis of 25 growth rings is 0.2, suggesting that a climate with abundant rainfall and weak seasonality could have prevailed in Yunnan, at least locally, during the Middle Jurassic. The outer portion of the wood is largely decayed, and shows poorly preserved cells lacking details. Decayed tracheids displaying various features, including removal of middle lamellae, separations of secondary walls, presence of thickened corners and appositions, are recognised as cell reactions to fungal activity. Irregularly distributed micro-cavities are formed by complete decomposition of tracheids and rays in the wood. Abundant fungal remains occurring in the wood generally consist of multiple branched hyphae. These fungal hyphae are either confined to individual cell lumens or extend through adjacent cells. Although the probable reproductive structure and typical clamp connection are very rarely observed with few septate hyphae, the affinities of these fungal hyphae are somewhat obscure. Nevertheless, our study sheds light on the palaeoecology of Middle Jurassic terrestrial ecosystems of Southwest China.