大花序桉心边材变异规律和候选基因挖掘研究

为探究大花序桉(Eucalyptus cloeziana)心材比例差异显著的不同家系间心边材变异规律,挖掘心材变异相关的候选基因,为珍贵用材树种高效培育及育种利用提供基因资源。以18 a生的2个心材比例差异显著的大花序桉家系为材料(家系1和2),各制作解析木3株,沿着树干以1 m为区间分段截取圆盘,测量东西和南北2个方向的带皮直径、去皮直径、总年轮数、边材年轮数、边材直径,并开展心材和边材径向和轴向分析。同时利用各解析木胸径处初生木质部样品进行DNA混池测序,发掘等位基因频率差异显著的SNP位点并挖掘相关功能基因。结果表明,大花序桉边材宽度和心材半径的方位变异中家系2大于家系1,平均差值分别为0.7和5.5 cm,在随树高的变异中,家系1和2的心材半径和心材年轮数的下降速率分别为0.40和0.64及0.43和0.36。两家系间基本密度差异显著,家系1为0.80～0.82 g/cm³,家系2为0.75～0.78 g/cm³。基本密度与树高、横截面半径和心材半径呈显著负相关,与顺纹抗拉强度、弦面硬度和部分力学性质呈显著正相关。利用DNA混池测序共...     

From desert to rainforest, sapwood width is similar in the widespread conifer Callitris columellaris

The process that transforms conductive sapwood to non-conductive heartwood in trees is poorly understood. Here, we use natural variation in climate to examine the environmental control of sapwood width in a widespread conifer species. We hypothesised that if sapwood width is linked to transpirational load, there would be a positive association between sapwood width, and continental gradients in mean annual rainfall, whereas age-related conversion to heartwood would be revealed from estimates of the age of the inner-most sapwood ring. Using the widespread Australian conifer Callitris columellaris we took cores from trees at 85 sites spanning a range of 168–2,117 mm in mean annual rainfall, and 14–28 °C in mean annual temperature. We found that sapwood width was remarkably similar throughout the species range, being only slightly lower in the tropics than the arid or temperate zone. There was a weak negative relationship between sapwood width and mean annual rainfall, which is in the opposite direction expected from transpirational control of sapwood width. Sapwood growth rings were wider, but there were fewer of them in the tropics than elsewhere, indicating conversion to heartwood occurred earlier here. Together with an earlier finding that tracheid diameter was largest in the tropics, our results show that differences amongst climate zones more strongly influence the hydraulic properties of sapwood than its amount.     

Xylem water content and wood density in spruce and oak trees detected by high-resolution computed tomography

Elucidation of the mechanisms involved in long-distance water transport in trees requires knowledge of the water distribution within the sapwood and heartwood of the stem as well as of the earlywood and latewood of an annual ring. X-ray computed tomography is a powerful tool for measuring density distributions and water contents in the xylem with high spatial resolution. Ten- to 20-year-old spruce (Picea abies L. KARST.) and oak (Quercus robur) trees grown in the field were used throughout the experiments. Stem and branch discs were collected from different tree heights, immediately deep frozen, and used for the tomographic determinations of spatial water distributions. Results are presented for single-tree individuals, demonstrating heartwood and sapwood distribution throughout their entire length as well as the water relations in single annual rings of both types of wood. Tree rings of the sapwood show steep water gradients from latewood to earlywood, whereas those of the heartwood reflect water deficiency in both species. Although only the latest two annual rings of the ringporous species are generally assumed to transport water, we found similar amounts of water and no tyloses in all rings of the oak sapwood, which indicates that at least water storage is important in the whole sapwood.     

Heartwood and sapwood development within maritime pine (<Emphasis Type="Italic">Pinus pinaster </Emphasis>Ait.) stems

Heartwood and sapwood development in maritime pine (Pinus pinaster Ait.) is reported based on 35 trees randomly sampled in four sites in Portugal. It was possible to model the number of heartwood rings with cambial age. The heartwood initiation age was estimated to be 13 years and the rate of sapwood transformation into heartwood was 0.5 and 0.7 rings year^–1 for ages below and above 55 years, respectively. Reconstruction of heartwood volume inside the tree stem was made by visual identification by image analysis in longitudinal boards along the sawn surfaces. This volume was integrated into the 3D models of logs and stems developed for this species representing the external shape and internal knots. Heartwood either follows the stem profile or shows a maximum value at 3.8 m in height, on average, while sapwood width is greater at the stem base and after 3 m remains almost constant up the stem. Up to 50% of tree height heartwood represents 17% of stem volume, in 83-year-old trees and 12–13% in 42 to 55-year-old trees. Tree variables such as stem diameter, DBH and tree total height were found to correlate significantly with the heartwood content.     

Estimating missing sapwood rings in three European gymnosperm species by the heartwood age rule

Precise dating of the year of felling is one intended outcome of dendrochronology. However, occasionally some or all sapwood rings might be missing, either due to deterioration or because they were carved off, or for some other reason. Consequently, while heartwood is preserved, sapwood might be fully or partially missing. In such cases, the year of felling must be estimated by adding a suitable number of sapwood rings. A heartwood age rule (HAR) has been advocated for Scots pine and adapted to European larch and Cembra pine, implying a linear relationship between sapwood ring count and the square root of heartwood ring count, largely irrespective of position in the stem. The same rule applied to all observations of a species, irrespective of silviculture, location or fertility of the growth site. Scots pine had twice or thrice as many sapwood rings as Cembra pine, which had 10% more rings than larch. The magnitude of model residuals was proportional to estimated sapwood ring count. Relative residuals were roughly normally distributed. To be applicable in Bayesian modelling in dendrochronology analyses, detailed information on model errors has been provided.     

The Zurich method for sapwood estimation

We present a new predictor for the estimation of the number of missing sapwood rings in oak. It circumvents a number of problems with predictors used in traditional sapwood estimation procedures such as mean ring width or tree age. Instead, we use the mean ring width of the last 9 heartwood rings and the first sapwood ring, which mirrors the growth level during sapwood formation. We present a model to produce a 95 % prediction interval for the felling year. Our method accounts for the skewed distribution of the number of sapwood rings towards higher values.     

Formation and vertical distribution of sapwood and heartwood in Cryptomeria japonica D. Don

The formation and vertical distribution of sapwood and heartwood were studied with a 45-year-old Cryptomeria japonica D. Don. The tree was grown at a plantation with 1.5 m × 3.0 m spacing near Miao-Li, Taiwan and was felled on 27 February 1992. The thickness of sapwood and heartwood was expressed by a ring count and a linear measurement. The east-west (E-W) wood strips were collected from 0.3 m above ground upwards to the top of the tree at 2.5 m intervals. The sapwood thicknesses from the base to the 10.3 m tree level height are around 20–22 growth rings and 42±2 mm. At the top of the tree, the sapwood thickness is narrower. The heartwood, which decreases in thickness with increasing tree level heights is not found at the top of the tree. The heartwood appears as a conical shape in the tree trunk. There is no statistical difference in sapwood/heartwood thickness between E-W aspects. Tree level heights and the tree level age were found to be important parameters in determining the thickness of sapwood/heartwood.     

BAI BAI bias – An evaluation of uncertainties in calculating basal area increments from cores

Basal area increment (BAI) is increasingly used in tree-ring based studies as it provides a direct measure of wood production and thus allows for the interpretation of growth trends. BAIs from increment cores are generally calculated while assuming circular growth patterns. However, observation of stem discs shows that many ring shapes are characterized by some form of eccentricity, not only characterized by deviations from circular ring shapes but also by piths not being centrally located. This observation poses to the question with what accuracy BAIs are calculated from increment cores. To quantify the estimation bias in BAI, we have developed a method that mimics eccentric tree growth by simulation. Various aspects of eccentricity are incorporated to created ‘stem discs’ with realistic appearances. Since BAI time series for our simulated discs are known, we can evaluate the accuracy of BAI calculation methods from cores. The ‘coring’ is simulated by taking cores at the thickest and thinnest sides of the simulated discs, whereby the number of cores is varied from one to four. In our simulations, we choose two calculation methods, namely the traditional circular approach and one that is based on the assumption of elliptical growth shapes. We find that bias in calculated BAI values is highly influenced by the number of cores taken, with a dramatic decrease from one to four cores. Furthermore, trend patterns in BAI series might be misleading in case of highly eccentric growth patterns. Based on these findings, we discuss the consequences for the interpretation of existing literature, where BAI analyses are based on one or two cores (along with the assumption of circular ring shapes). Such consequences are, however, difficult to quantify since we have no eccentricity statistics of tree growth within a forest stand. Therefore, we do not know the randomness of eccentricity within a stand, and thus to what extent chronology building (i.e. averaging BAI estimates over multiple trees) may reduce estimation bias. To lower BAI bias, we recommend to base BAI calculations on as many cores as possible. For individual trees with high levels of eccentricity, taking four increment cores seems necessary to reasonably estimate their basal area increments.     

A statistical model for the prediction of the number of sapwood rings in Scots pine (Pinus sylvestris L.)

Dendrochronology is a well-established dating method for wooden objects, but due to surface processing of construction timber or natural degradation the dating of historical wood often relies on a prediction of the number of missing rings based on sapwood statistics. Since Scots pine (Pinus sylvestris L.) is one of the most common tree species in north-western Europe, the absence of reliable sapwood statistics and models for the prediction of missing sapwood rings for pine samples is remarkable. We have therefore produced sapwood statistics based on data from 776 pine trees with ages from 15 to 345 years. The material consists of both living trees and historical timber, with varying growth rates, geographic settings, and from different soil types. When the whole material is considered, the average age of the trees is 103 years, and the number of sapwood rings is 54 ± 15 (1 SD), but range from 18 to 129. Trees less than 100-years in age contained 46 ± 11 (1 SD) sapwood rings and had an average tree-ring width (TRW) of 1.76 mm. With increasing age, the average TRW decreased while the number of sapwood rings increased. The average TRW of 101–200-year-old trees is 0.99 mm while the samples contained 63 ± 12 (1 SD) sapwood rings. For trees older than 201 years, the average TRW is 0.64 mm while the number of sapwood rings increased to 85 ± 16 (1 SD). The two most important factors in determining the number of sapwood rings for a given tree when only heartwood statistics are available proved to be (i) the number of heartwood rings and (ii) the average TRW of the heartwood rings. For incomplete samples, we have therefore developed a statistical model based on the sample’s heartwood rings (number and average width) to compute a prediction interval for the total number of rings. The sapwood and heartwood statistics suggest a statistical model for the number of sapwood rings with mean that increase with the number of heartwood rings. Furthermore, the average number of sapwood rings decreases with the mean width of the heartwood rings. However, the predictive power of the mean width is limited when the number of heartwood rings has already been taken into account. Thus, we suggest making predictions for the number of sapwood rings using only the number of heartwood rings. Predictions of the number of sapwood rings based on the statistical model where convincing in the case of the three different datasets that were analysed. The certainty in these predictions was such that the width of the 80% and 95% prediction intervals ranged 28–34 and 45–52 sapwood rings, respectively. Additionally, we demonstrate how make predictions when there is information about the number of remaining sapwood rings in a given sample. To make the sapwood model available, we present a free online R package for fitting our models and an online software dashboard.     

Respiration in the sapwood and heartwood of Robinia pseudoacacia

The respiratory activity of distinct sapwood and heartwood annual rings of the stem of Robinia pseudoacacia L. has been investigated. The oxygen uptake and the carbon dioxide release in the inner parts of the sapwood is enhanced in comparison with that in the outer parts. The heartwood rings have no measureable gas exchange.     

Sapwood characteristics of Quercus robur species from the south-western part of the Pannonian Basin

We analysed sapwood characteristics in 344 pedunculate oak (Quercus robur L.) samples from the south-western part of the Pannonian Basin. The samples came from 13 sites, located in Slovenia, Croatia and Serbia. The trees had an average of 13.3 sapwood rings, with a minimum of 5 and maximum of 32. Fifteen log-log linear regression models were employed to assess the statistical relationship between sapwood and heartwood variables. The number of sapwood rings (N_SW), which is usually needed in dendroarchaeological dating, is significantly related to the number of heartwood rings (N_HW), heartwood width (W_HW) and heartwood growth rate (G_HW). Older and more slowly growing trees had a higher average number of sapwood rings. Using N_HW and W_HW, we employed an additional multiple regression model and calculated coefficients for N_SW predictions for real-world dendroarchaeological dating from the south-western part of the Pannonian Basin.     

Development of heartwood in response to water stress for radiata pine in Southern New South Wales, Australia

Heartwood development and other functional changes in stem conductance in response to water stress in radiata pine were investigated using two contrasting climatic areas (high-altitude sub-alpine vs. warm–dry inland) of the Hume region of New South Wales, Australia. The study included mature (34.5–36.5 years old) and young stands (10–11 years old) measured under normal climate and during an extreme drought. The effect of water stress on heartwood development was examined using sapwood percentage, sapwood saturation, development of dry sapwood and evidence of cavitation in sapwood. Trees at the warm–dry site developed heartwood at faster rates than on the high-altitude site. At breast height, the mature stands of the warm–dry site had 8–14 % less sapwood. Extensive cavitation towards the sapwood/heartwood boundary occurred in some of the mature and young stands on the warm–dry site. We postulated that in water-limiting environments, cavitation of the inner sapwood precedes heartwood formation and is an adaptation mechanism that regulates stem conductance capacity and thus water use in the tree. The drought of 2006 led to decreases in moisture associated with cavitation not previously reported for radiata pine and demonstrated the drought hardiness of the species. In the warm–dry site, breast-height sapwood saturation dropped to 58 and 82 % for suppressed and average-sized trees in a mature unthinned stand; and 75–78 % for two young stands. These saturation levels, however, only imply average values as some cells cavitated whilst others were fully saturated. Cavitation occurred in a localized fashion affecting small to large groups of cells.     

Variation of different tree-ring parameters in samples from each terminal shoot of a Norway spruce tree

Variability of wood parameters in a tree is sometimes a rather nebulous concept since variability is evident within single cells, from early to latewood, from pith to bark and from stem base to the top of a tree. So far, stem analyses have been done using a restricted number of parameters, mostly ring-width, and using a restricted number of samples in the longitudinal direction. This study analyses a number of parameters from a single tree. An 81-year-old spruce tree was felled and internodial discs were taken from each annual terminal shoot. All tree rings in each disc were measured and a whole-stem analysis was completed for the following parameters: ring-width, mean ring density, maximum density, percentage of latewood, type of transition from early to latewood, intra-annual density fluctuation, number of resin ducts per tree-ring and position of resin ducts within the tree-rings. All parameters showed calendar-year patterns, visible as lines parallel to the bark. The most clear calendar-year pattern was seen for the type of transition from early to latewood and for intra-annual density fluctuations. The strongest inter-series correlation between calendar rings was seen for ring-width. None of the parameters showed significant inter-series correlations for cambial rings. These results may help us to understand how cores or discs taken at breast height represent the entire tree.     

Variation of different tree-ring parameters in samples from each terminal shoot of a Norway spruce tree

Variability of wood parameters in a tree is sometimes a rather nebulous concept since variability is evident within single cells, from early to latewood, from pith to bark and from stem base to the top of a tree. So far, stem analyses have been done using a restricted number of parameters, mostly ring-width, and using a restricted number of samples in the longitudinal direction. This study analyses a number of parameters from a single tree. An 81-year-old spruce tree was felled and internodial discs were taken from each annual terminal shoot. All tree rings in each disc were measured and a whole-stem analysis was completed for the following parameters: ring-width, mean ring density, maximum density, percentage of latewood, type of transition from early to latewood, intra-annual density fluctuation, number of resin ducts per tree-ring and position of resin ducts within the tree-rings. All parameters showed calendar-year patterns, visible as lines parallel to the bark. The most clear calendar-year pattern was seen for the type of transition from early to latewood and for intra-annual density fluctuations. The strongest inter-series correlation between calendar rings was seen for ring-width. None of the parameters showed significant inter-series correlations for cambial rings. These results may help us to understand how cores or discs taken at breast height represent the entire tree.     

Comparing automatically generated and manually measured tree-ring transects of growth trends with Hawaiian sandalwood as an example species

Tree-ring measurements are a primary quantitative tool used in numerous scientific disciplines. Some species, however, exhibit morphological complexities leading to significant uncertainty in these measurements. Hawaiian Sandalwood (Santalum paniculatum) stems, for example, often develop asymmetric growth features that hinder tree-ring measurements. These features include faint-ring boundaries and wedging rings which disappear in portions of the cross-section. In this work we a use a novel two-dimensional transect methodology and our own open-source software, svg-dendro, to analyze particularly difficult cross-sections. Our method accomplishes this by first tracing all rings by hand and automatically generating a user-specified number of transects. On average, these traced measurements had more sensitivity to tree-ring variability without losing important equivalencies with the traditional binocular stereomicroscope technique (e.g., radii, skewness) as indicated by greater mean variance for ring number, mean tree-ring width, and standard deviation. All S. paniculatum samples had ring wedging, where certain sides of the stem had many locally absent tree rings but to different intensities. The new technique allows us to analyze the shift from complete rings with little to no wedging to rings with more wedging starting between the 19th and 40th ring, where deep stem lobes begin forming. The new method also reveals the difficulty in measuring these trees, as the wedging creates multiple lobes with different visible ring counts. This research suggests that this two-dimensional methodology would be best applied to non-circular trees with fewer incomplete rings, supporting the importance of species and population selection. Overall, we have developed an efficient and flexible means to measure otherwise unmeasurable growth features in tree samples through representing tree-ring boundaries as curves and developing software to sort and map transects.     

Lipids and sterols of Pinus sylvestris L. sapwood and heartwood

Summary The lipid and sterol content and composition of three lipid fractions (free fatty acids/ sterols, triacylglycerols and sterol/triterpenoid esters) extracted from three stem discs of Pinus sylvestris were assessed to investigate metabolic changes related to heartwood formation. The wood was separated into (1) cambial zone, (2) outer sapwood, (3) inner sapwood, (4) transition zone, (5) outer heartwood and 6) inner heart-wood. The fractions were separated by thin-layer chromatography (TLC) and analysed by gas-liquid chromatography (GLC). The amount of fatty acids of sapwood triacylglycerols was about 1.5% (dry wt.) but a large reduction occurred in the transition zone. In contrast, noticeable amounts of free fatty acids were present only in the heart-wood. The most important fatty acids in the sapwood fractions were 16:0, 18:0, 18:1, 18:2 (the dominant fatty acid in all fractions), 18:3 and 20:3. Together 18:1 and 18:2 formed about 70% of the total triacylglycerol fatty acids. Of the sterol/ triterpenoid esters, 18:2 and 18:3 were predominant. The fatty acid composition of all fractions changed in the transition zone. The sterols found were sitosterol, stigmastanol, campesterol and campestanol. The amount of sterol esters increased towards the heartwood, and the amount of free sterols was lowest in the inner sapwood. Sitosterol was the dominant sterol in both free sterols and sterol esters.     

Relationship of heartwood traits with diameter growth, implications for genetic selection in Pinus radiata

The heartwood of radiata pine (Pinus radiata D. Don) is not favoured commercially because of its darker appearance, unreliable durability and difficulty to treat chemically; consequently, light-coloured sapwood, which is more easily treated with decay-resistant chemicals, is of more value. To decrease the amount of heartwood or increase sapwood cross-sectional area by genetic selection, the genetics of sapwood cross-sectional area (SWA), sapwood area percentage (SWAP) and number of heartwood rings (HWR) is of interest. We investigated genetic variation in these three variables from increment cores from trees from two trial series, each planted at two sites, from a total of some 330 families (189 were half-sib and 142 were full-sib) with 10 to 30 individuals assessed per family. Trials were assessed between 16 and 23 years old when all trees had started to develop heartwood. The three sapwood-related traits were moderately heritable across pairs of sites ( h ^ i 2 $ {\widehat{h}}_i^2 $ = 0.2 to 0.4) indicating opportunity for selection. SWA was strongly correlated (r _a ?=?0.9) with diameter. SWAP and HWR were also strongly correlated (r _a ?=??0.9). The number of HWR was independent of tree diameter, providing the opportunity through genetic selection to reduce heartwood area whilst increasing tree growth rate.     

The function of intercellular spaces along the ray parenchyma in sapwood, intermediate wood, and heartwood of Cryptomeria japonica (Cupressaceae)

? Premise of the study: Intercellular spaces along ray parenchyma (ISRP) are common in many conifer xylems, but their function is uncertain because the in-situ structural network among ISRP, ray parenchyma, and tracheids has not been evaluated. Analysis of water distribution in ISRP from sapwood to heartwood is needed to elucidate the function of ISRP in sapwood, intermediate wood, and heartwood. ? Methods: We used cryo-scanning electron microscopy, x-ray photography, and water content measurement in xylem to analyze the presence of liquids in ISRP, ray parenchyma, and tracheids from sapwood to heartwood in Cryptomeria japonica (Cupressaceae). ? Key results: In sapwood, almost all ISRP were empty. "Cingulate-cavitated regions", which lose water along the tangential direction within one annual ring, formed in the earlywood tracheids, and their frequency increased toward the inner annual rings, whereas ray parenchyma cells were alive and not involved in the partial cavitation. In intermediate wood, almost all ISRP and earlywood tracheids and many of the ray cells were empty, and only some latewood tracheids retained liquid in their lumina. The ISRP were connected with tracheids via gas-filled ray parenchyma cells. ? Conclusions: The ISRP work as a pathway of gas for aspiration of ray parenchyma cells in sapwood. On the other hand, the occurrence of a gas network between ISRP, ray parenchyma, and tracheids facilitates cavitation of tracheids, resulting in the generation of low-moisture, intermediate wood.     

Notes towards an optimal sampling strategy in dendroclimatology

Though the extraction of increment cores is common practice in tree-ring research, there is no standard for the number of samples per tree, or trees per site needed to accurately describe the common growth pattern of a discrete population of trees over space and time. Tree-ring chronologies composed of living, subfossil and archaeological material often combine an uneven distribution of increment cores and disc samples. The effects of taking one or two cores per tree, or even the inclusion of multiple radii measurements from entire discs, on chronology development and quality remain unreported. Here, we present four new larch (Larix cajanderi Mayr) ring width chronologies from the same 20 trees in northeastern Siberia that have been independently developed using different combinations of core and disc samples. Our experiment reveals: i) sawing is much faster than coring, with the latter not always hitting the pith; ii) the disc-based chronology contains fewer locally absent rings, extends further back in time and exhibits more growth coherency; iii) although the sampling design has little impact on the overall chronology behaviour, lower frequency information is more robustly obtained from the disc measurements that also tend to reflect a slightly stronger temperature signal. In quantifying the influence of sampling strategy on the quality of tree-ring width chronologies, and their suitability for climate reconstructions, this study provides useful insights for optimizing fieldwork campaigns, as well as for developing composite chronologies from different wood sources.