植物激素与木材形成

综述了植物激素在树木维管组织分化中的作用．生长素是调节木质部细胞分化的主要因子；细胞分裂素在诱导分生组织发端和分生细胞分化上起重要作用；赤霉素促进纤维的形成，赤霉素和生长素结合使用，可有效地促进次生木质部中纤维分化；乙烯能促进树木韧皮部和木质部分化。还讨沦了木材形成过程中的三个主要问题：生长素含量的多少直接控制了沿树轴木质部导管、管胞的大小和密度；外界环境因子影响木质部细胞分化；温带落叶阔叶树环孔材和散孔材形成的机理，生长素控制环孔材树种早材宽导管的形成以及晚材窄导管和纤维形成的假说。对今后改善树木木材的质和量上有一定参考价值。     

Variation in drought response of sal (Shorea robusta) seedlings

Plant development and distribution in areas with seasonal rainfall are often related to the ability of plants to postpone desiccation or tolerate low water potentials during drought. Regeneration of Shorea robusta Gaertn. (sal), a commercially valuable, widely distributed tree of the Indian tropical belt, is unsuccessful at the base of the Himalaya. Seedling shoots die back repeatedly during the long drought that follows the monsoon rain. During the course of one year, we monitored changes in plant and soil water potentials (Psi), leaf conductance (gw), osmotic and elastic adjustment, and xylem conductance of sal seedlings of different sizes from three landforms: an alluvial plain at 540 m elevation, a slope at 510 m, and a montane site at 1370 m. Predawn plant Psi and gw were lowest in the smallest seedlings (< 20 cm tall). Across sites and seasons, seedlings > 100 cm tall had higher morning gw than seedlings in the other size classes. In all size classes, plant Psi was lowest during early summer, when leafing begins. Among sites, Psi and gw were lowest in seedlings at the montane site. Osmotic potential was lowest during leaf development and highest during the rainy season, and tissue elasticity was highest during winter. As leaf area increased during leaf development, xylem conductance per unit of xylem cross-sectional area also increased. We conclude that low Psi is unlikely to be a major cause of seedling mortality. Small seedlings, with low Psi, had low leaf conductance. Adjustments of osmotic and elastic properties appear to aid responses of seedlings to drought.     

Lignin deposition during earlywood and latewood formation in Scots pine stems

Lignin deposition at consecutive secondary wall thickening stages of early and late xylem cells during annual ring wood formation in Scots pine (Pinus sylvestris L.) stems was studied. Lignin patterns, isolated by thioglycolic acid method, consisted of alcohol-soluble (LTGA-I) and alkali-soluble (LTGA-II) fractions. The sum of two fractions, being the total lignin content, gradually increased in the course of lignification. However, the increments of lignin amount at each development stage of early and late tracheids were different. The intensity of lignin deposition increased in the course of earlywood tracheid maturation and decreased toward the end of latewood cell differentiation. The deposition of two lignin fractions in each layer of forming wood also occurred oppositely. The increment of LTGA-I descended, whereas that of LTGA-II increased from the beginning to the end of early xylem lignification. In contrast, LTGA-I increment dropped, whereas LTGA-II rose during late xylem lignification. Gel permeation chromatography showed that the lignins, formed at the beginning of lignification, were more homogeneous and had higher molecular weight compared with the lignins at the end of cell differentiation. Besides, the content of cellulose, estimated as the residue after lignin isolation, and of cell wall substances, presented as cell wall cross-section areas, at consecutive maturation stages of early and late xylem cells have been found to be different. The data show that lignin deposition occurred in different conditions and with opposite dynamics during early and late xylem formation.     

Coast live oak, Quercus agrifolia, susceptibility and response to goldspotted oak borer, Agrilus auroguttatus, injury in southern California

Oak mortality is often associated with a complex of decline factors. We describe the morphological and physiological responses of coast live oak, Quercus agrifolia Née, in California to an invasive insect, the goldspotted oak borer (GSOB), Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), and evaluate drought as a potential inciting factor. Morphological traits of 356 trees were assessed and physiological traits of 70 of these were monitored intensively over one growing season. Morphological characteristics of tree health included crown thinning and dieback; bole staining resulting from larval feeding; density of GSOB adult exit holes; and holes caused by woodpecker feeding. These characteristics were used to rank GSOB infestation/injury into four classes, and taken together, they explained 87% of the variation in a principal component analysis. Drought stress on various size/age and infestation classes of Q. agrifolia was measured by assessing branchlet pre-dawn and solar noon xylem water potential, leaf cell turgor potential, and water use efficiency over one growing season. Both morphological and physiological traits were highly variable in mature and old growth trees. Early summer plant water status (branchlet xylem water potential and water use efficiency) was similar between uninfested and newly colonized trees, suggesting that GSOB are not pre-selecting drought-stressed Q. agrifolia for oviposition. By late summer, leaf water and cell turgor potentials were lower in infested than in uninfested mature trees, suggesting that GSOB infestation causes drought stress in these trees. Among the tree size/age classes, infested old growth trees exhibited the greatest change in water use efficiency over the growing season, and showed greater morphological injury symptoms of decline than infested mature trees. Morphological attributes of decline in Q. agrifolia associated with GSOB were correlated weakly with increasing physiological drought stress among infestation classes of trees. We propose that the collection of morphological responses of Q. agrifolia to GSOB described here can be used to monitor the future expansion of the GSOB distribution as well as the GSOB-induced decline of Q. agrifolia in California.     

Variation in drought resistance, drought acclimation and water conservation in four willow cultivars used for biomass production

Growth and water-use parameters of four willow (Salix spp.) clones grown in a moderate drought regime or with ample water supply were determined to characterize their water-use efficiency, drought resistance and capacity for drought acclimation. At the end of the 10-week, outdoor pot experiment, clonal differences were observed in: (1) water-use efficiency of aboveground biomass production (WUE); (2) resistance to xylem cavitation; and (3) stomatal conductance to leaf-specific, whole-plant hydraulic conductance ratio (g(st)/K(P); an indicator of water balance). Across clones and regimes, WUE was positively correlated with the assimilation rate to stomatal conductance ratio (A/g(st)), a measure of instantaneous water-use efficiency. Both of these water-use efficiency indicators were generally higher in drought-treated trees compared with well-watered trees. However, the between-treatment differences in (shoot-based) WUE were smaller than expected, considering the differences in A/g(st) for two of the clones, possibly because plants reallocated dry mass from shoots to roots when subject to drought. Higher root hydraulic conductance to shoot hydraulic conductance ratios (K(R)/K(S)) during drought supports this hypothesis. The same clones were also the most sensitive to xylem cavitation and, accordingly, showed the strongest reduction in g(st)/K(P) in response to drought. Drought acclimation was manifested in decreased g(st), g(st)/K(P), osmotic potential and leaf area to vessel internal cross-sectional area ratio, and increased K(R), K(P) and WUE. Increased resistance to stem xylem cavitation in response to drought was observed in only one clone. It is concluded that WUE and drought resistance traits are inter-linked and that both may be enhanced by selection and breeding.     

Understanding the role of the cytoskeleton in wood formation in angiosperm trees: hybrid aspen (Populus tremula x P. tremuloides) as the model species

The involvement of microfilaments and microtubules in the development of the radial and axial components of secondary xylem (wood) in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) was studied by indirect immunofluorescent localization techniques. In addition to cambial cells, the differentiated cell types considered were early- and late-wood vessel elements, axial parenchyma, normal-wood fibers and gelatinous fibers, and contact and isolation ray cells. Microfilaments were rare in ray cambial cells, but were abundant and axially arranged in their derivatives once cell elongation had begun, and persisted in that orientation in mature ray cells. Microfilaments were axially arranged in fusiform cambial cells and persisted in that orientation in all xylem derivatives of those cells. Microtubules were randomly oriented in ray and fusiform cells of the cambial zone. Dense arrays of parallel-aligned microtubules were oriented near axially in the developing gelatinous fibers, but at a wide range of angles in normal-wood fibers. Ellipses of microfilaments were associated with pit development in fiber cells and isolation ray cells. Rings of co-localized microtubules and microfilaments were associated with developing inter-vessel bordered pits and vessel-contact ray cell contact pits, and, in the case of bordered pits, these rings decreased in diameter as the over-arching pit border increased in size. Although only microtubules were seen at the periphery of the perforation plate of vessel elements, a prominent meshwork of microfilaments overlaid the perforation plate itself. A consensus view of the roles of the cytoskeleton during wood formation in angiosperm trees is presented.     

Bole girdling affects metabolic properties and root, trunk and branch hydraulics of young ponderosa pine trees

Effects of trunk girdling on seasonal patterns of xylem water status, water transport and woody tissue metabolic properties were investigated in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws.) trees. At the onset of summer, there was a sharp decrease in stomatal conductance (g(s)) in girdled trees followed by a full recovery after the first major rainfall in September. Eliminating the root as a carbohydrate sink by girdling induced a rapid reversible reduction in g(s). Respiratory potential (a laboratory measure of tissue-level respiration) increased above the girdle (branches and upper trunk) and decreased below the girdle (lower trunk and roots) relative to control trees during the growing season, but the effect was reversed after the first major rainfall. The increase in branch respiratory potential induced by girdling suggests that the decrease in g(s) was caused by the accumulation of carbohydrates above the girdle, which is consistent with an observed increase in leaf mass per area in the girdled trees. Trunk girdling did not affect native xylem embolism or xylem conductivity. Both treated and control trunks experienced loss of xylem conductivity ranging from 10% in spring to 30% in summer. Girdling reduced xylem growth and sapwood to leaf area ratio, which in turn reduced branch leaf specific conductivity (LSC). The girdling-induced reductions in g(s) and transpiration were associated with a decrease in leaf hydraulic conductance. Two years after girdling, when root-to-shoot phloem continuity had been restored, girdled trees had a reduced density of new wood, which increased xylem conductivity and whole-tree LSC, but also vulnerability to embolism.     

Radial variation in sap flow in five laurel forest tree species in Tenerife,Canary Islands

Variations in radial patterns of xylem water content and sap flow rate were measured in five laurel forest tree species (Laurus azorica (Seub.) Franco, Persea indica (L.) Spreng., Myrica faya Ait., Erica arborea L. and Ilex perado Ait. ssp. platyphylla (Webb & Berth.) Tutin) growing in an experimental plot at Agua García, Tenerife, Canary Islands. Measurements were performed around midday during warm and sunny days by the heat field deformation method. In all species, water content was almost constant (around 35% by volume) over the whole xylem cross-sectional area. There were no differences in wood color over the whole cross-sectional area of the stem in most species with the exception of E. arborea, whose wood became darker in the inner layers. Radial patterns of sap flow were highly variable and did not show clear relationships with tree diameter or species. Sap flow occurred over the whole xylem cross-sectional area in some species, whereas it was limited to the outer xylem layers in others. Sap flow rate was either similar along the xylem radius or exhibited a peak in the outer part of the xylem area. Low sap flow rates with little variation in radial pattern were typical for shaded suppressed trees, whereas dominant trees exhibited high sap flow rates with a peak in the radial pattern. Stem damage resulted in a significant decrease in sap flow rate in the outer xylem layers. The outer xylem is more important for whole tree water supply than the inner xylem because of its larger size. We conclude that measurement of radial flow pattern provides a reliable method of integrating sap flow from individual measuring points to the whole tree.     

毛白杨枝条木质部细胞分化的动态变化及其与形成层活动的相互关系

应用定量解剖学和显微图像分析技术 ,得到了毛白杨枝条形成层细胞与其衍生木质部细胞解剖特征在形成层活动期内的变化情况 ,并探讨了两者之间的关系。采用X射线微密度测定技术 ,了解了同一生长轮内木材密度沿径向方向上的变异 ,讨论了其与木质部细胞解剖特征之间的关系。结果表明 ,形成层纺锤形细胞的径向和弦向宽度在活动期不同阶段差异不显著 ,而纤维长度、纤维宽度、壁腔比、微纤丝角、导管分布频率和胞壁率差异极显著 ;导管组织比量差异显著 ;导管分子长度、纤维比量和射线比量差异不显著。同一生长轮内木材密度的径向变异与活动期不同阶段形成的木质部细胞数量及其解剖特征直接相关。形成层带细胞层数与纤维长度、纤维长宽比和壁腔比呈极显著负相关 ,与纤维宽度呈显著正相关 ;形成层纺锤形细胞的径向宽度与纤维长度、纤维长宽比和射线比量呈显著负相关 ;形成层纺锤形细胞的弦向宽度与纤维宽度呈显著正相关。总体看来 ,在整个形成层活动期 ,形成层纺锤形细胞与木纤维的解剖特征之间随时间变化的相关性较好 ,而与导管分子的相关关系则不明显     

Influence of water relations on Quercus cerris-Hypoxylon mediterraneum interaction: a model of drought-induced susceptibility to a weakness parasite

The association between water stress and susceptibility of Quercus cerris to the fungal parasite Hypoxylon mediterraneum was studied in field-grown trees and greenhouse-grown seedlings. Susceptibility of Q. cerris to the fungus, expressed as extension of wood discolorations, increased in field-grown trees during drought and increased in greenhouse-grown seedlings in response to limited water supply. In both seedlings and trees, spread of the fungus in the vascular system was higher when leaf water potentials were low than when leaf water potentials were high, and was significantly correlated to loss of hydraulic conductivity of xylem. The presence of the fungus in the xylem suggests that H. mediterraneum could use embolized vessels to spread in the host.     

Anatomical and FTIR analyses of phloem and xylem of <Emphasis Type="Italic">Tetracentron sinense</Emphasis>

The fast growth of Tetracentron sinense is a potential valuable timber resource, but whether its anatomy and chemical components are suitable for timber is unknown. We used light microscopy and SEM to examine the anatomical structure and FITR to measure the chemical components of the phloem and xylem of this tree. Radial variations in growth ring width and tracheid dimensions were also evaluated. The sieve tube, phloem parenchyma cell and sclereids clusters were the main cells in phloem, and the tracheid was the fundamental cell in xylem. An unusual tracheid type, fiber-tracheids or vessel-liked elements was visible. Wood rays nonstoried, uniseriate and multiseriate, including heterogeneous II, occasionally I, and usually 3–6 cells wide. The mean growth-ring width was 2.53 ± 0.46 mm, and the percentage of late wood was over 60%. For radial variation, growth-ring width increased at an early growth stage, and reached the largest increment during years 11–15, then decreased. The maximum growth-ring width was 5.313 mm. During late growth (60–85 years), trees also maintained a high radial growth increment. Radial variation in the percentage of late wood was uniform, about 50–70%, throughout the growth years. Growth patterns in the length and width of early and late wood were similar as the trees aged. From the FTIR results, the chemical components differed significantly between xylem and phloem, hemicellulose in particular was higher in the xylem than in the phloem, where it was apparently absent. All of these suggest that the composition of phloem in T. sinense is very similar to that of hardwood, and it has higher growth ratio and uniform wood properties.     

Temperature effects on wood anatomy, wood density, photosynthesis and biomass partitioning of Eucalyptus grandis seedlings

Wood density, a gross measure of wood mass relative to wood volume, is important in our understanding of stem volume growth, carbon sequestration and leaf water supply. Disproportionate changes in the ratio of wood mass to volume may occur at the level of the whole stem or the individual cell. In general, there is a positive relationship between temperature and wood density of eucalypts, although this relationship has broken down in recent years with wood density decreasing as global temperatures have risen. To determine the anatomical causes of the effects of temperature on wood density, Eucalyptus grandis W. Hill ex Maiden seedlings were grown in controlled-environment cabinets at constant temperatures from 10 to 35 degrees C. The 20% increase in wood density of E. grandis seedlings grown at the higher temperatures was variously related to a 40% reduction in lumen area of xylem vessels, a 10% reduction in the lumen area of fiber cells and a 10% increase in fiber cell wall thickness. The changes in cell wall characteristics could be considered analogous to changes in carbon supply. Lumen area of fiber cells declined because of reduced fiber cell expansion and increased fiber cell wall thickening. Fiber cell wall thickness was positively related to canopy CO2 assimilation rate (Ac), which increased 26-fold because of a 24-fold increase in leaf area and a doubling in leaf CO2 assimilation rate from minima at 10 and 35 degrees C to maxima at 25 and 30 degrees C. Increased Ac increased seedling volume, biomass and wood density; but increased wood density was also related to a shift in partitioning of seedling biomass from roots to stems as temperature increased.     

Contrasting seasonal leaf habits of canopy trees between tropical dry-deciduous and evergreen forests in Thailand

We compared differences in leaf properties, leaf gas exchange and photochemical properties between drought-deciduous and evergreen trees in tropical dry forests, where soil nutrients differed but rainfall was similar. Three canopy trees (Shorea siamensis Miq., Xylia xylocarpa (Roxb.) W. Theob. and Vitex peduncularis Wall. ex Schauer) in a drought-deciduous forest and a canopy tree (Hopea ferrea Lanessan) in an evergreen forest were selected. Soil nutrient availability is lower in the evergreen forest than in the deciduous forest. Compared with the evergreen tree, the deciduous trees had shorter leaf life spans, lower leaf masses per area, higher leaf mass-based nitrogen (N) contents, higher leaf mass-based photosynthetic rates (mass-based P(n)), higher leaf N-based P(n), higher daily maximum stomatal conductance (g(s)) and wider conduits in wood xylem. Mass-based P(n) decreased from the wet to the dry season for all species. Following onset of the dry season, daily maximum g(s) and sensitivity of g(s) to leaf-to-air vapor pressure deficit remained relatively unchanged in the deciduous trees, whereas both properties decreased in the evergreen tree during the dry season. Photochemical capacity and non-photochemical quenching (NPQ) of photosystem II (PSII) also remained relatively unchanged in the deciduous trees even after the onset of the dry season. In contrast, photochemical capacity decreased and NPQ increased in the evergreen tree during the dry season, indicating that the leaves coped with prolonged drought by down-regulating PSII. Thus, the drought-avoidant deciduous species were characterized by high N allocation for leaf carbon assimilation, high water use and photoinhibition avoidance, whereas the drought-tolerant evergreen was characterized by low N allocation for leaf carbon assimilation, conservative water use and photoinhibition tolerance.     

Radial variations in the anatomical characteristics and density of the wood of Acacia mangium of five different provenances in Indonesia

The anatomical characteristics and density of wood were examined in 23-year-old Acacia mangium trees that had been planted in Yogyakarta, Indonesia. The seeds had been collected from trees of five different provenances. The distance from the pith of the boundary between juvenile and mature wood was also examined to clarify the maturity of the wood. Lengths of wood fibers near the pith and the distance from the pith of the boundary between juvenile and mature wood differed significantly among provenances. By contrast, other anatomical characteristics of the wood such as fiber wall area, fiber wall thickness, fiber diameter, vessel lumen area, vessel diameter, vessel frequency and wood density did not differ significantly among provenances. Wood density was strongly correlated with the area of fiber walls. Our observations suggest that Sidei and Daintree might be more appropriate provenances among those examined for the Acacia mangium tree-breeding programs in Indonesia that are aimed at improving wood quality, because these provenances are associated with longer initial wood fibers and narrower juvenile areas than the other provenances studied.     

Response of stomatal conductance to drought in ponderosa pine: implications for carbon and ozone uptake

To gain insight into the limitations imposed by a typical Mediterranean-climate summer drought on the uptake of carbon and ozone in the ponderosa pine (Pinus ponderosa Dougl. ex Laws.) ecosystem, we compared diurnal trends in leaf physiology of young trees in a watered and a control plot located in the Sierra Nevada Mountains, CA, USA (Blodgett Forest, 38 degrees 53' N, 120 degrees 37' W, 1315 m elevation). Predawn water potential of trees in the watered plot remained above -0.3 MPa throughout the growing season, whereas it dropped in the control plot from -0.24 to -0.52 MPa between late May and mid-August. Photosynthesis and stomatal conductance of trees in the watered plot were relatively insensitive to atmospheric vapor pressure deficit (VPD), whereas gas exchange of trees in the control plot varied with changes in soil water, VPD and temperature. Although the 1998 growing season was abnormally wet, we saw a pronounced drought effect at the control site. Over the 2 months following the onset of watering, carbon and ozone uptake were measured on three days at widely spaced intervals. Carbon uptake per unit leaf area by 1-year-old foliage of trees in the control plot was 39, 35 and 30% less, respectively, than in the watered plot, and estimated ozone deposition per unit leaf area (ozone concentration times stomatal conductance) was 36, 46 and 41% less.     

Canopy and hydraulic conductance in young, mature and old Douglas-fir trees

We tested for reductions in water transport with increasing tree size, a key component in determining whether gas exchange and growth are hydraulically limited in tall trees. During the summers of 1998 and 1999, we measured water transport with Granier-type, constant-heat sap flow probes, vapor pressure deficit, and leaf and soil water potentials in overstory Pseudotsuga menziesii (Mirb.) Franco trees in three stands differing in size and age (15, 32 and 60 m in height and about 20, 40 and 450 years in age, respectively) in a P. menziesii-dominated forest in the Pacific Northwest, USA. A total of 24 trees were equipped with sap flow sensors--six 60-m trees, nine 32-m trees and nine 15-m trees. Based on the sap flow measurements and leaf area information estimated from leaf area-sapwood area relationships, we estimated crown-averaged stomatal conductance (GS) and leaf-specific hydraulic conductance (KL). We tested the hypothesis that GS and KL vary inversely with tree height (15 > 32 > 60 m). Analysis of variance of GS ranked as 15 = 60 > 32 m during the early summer and 15 > 60 > 32 m during late season drought. Over the growing season, mean daily GS (+/- SE) was 29.2 +/- 4.4, 24.0 +/- 6.8 and 17.7 +/- 7.2 mmol m-2 s-1 for the 15-, 60- and 32-m trees, respectively. The value of K(L) differed among tree heights only during late season drought and ranked 15 > 32 = 60 m. A hydraulic mass balance suggests that greater sapwood conductivity in 60-m trees compared with 32- and 15-m trees is a likely cause for the departure of the above rankings from those predicted by height and leaf-to-sapwood area ratio.     

Dissimilar stem and leaf hydraulic traits suggest varying drought tolerance among co-occurring Eucalyptus grandis × E. urophylla clones

In South Africa, there is currently a phenomenon where a Eucalyptus grandis × E. urophylla clone is dying on a large scale, whereas co-occurring clones in the same plantation area remain healthy. No primary biotic pathogen has been isolated from these dying trees. However, the plantation region has endured severe drought conditions. We hypothesised that the specific E. grandis × E. urophylla clone dieback is due in part to the affected trees having an elevated drought vulnerability. We tested this hypothesis retrospectively by examining how the dying (branch dieback started) as compared with two healthy and co-occurring E. grandis × E. urophylla clones vary in branch xylem anatomy (water transport) and leaf stable carbon isotopes (gas exchange) across two levels of mean annual precipitation in the planted landscape. There was significant intra-hybrid variation in the range of studied hydraulic traits. It appeared that the dying clone is maladapted to drier field conditions relative to the two healthy growing clones. Individuals of the drought-susceptible clone had increased hydraulic conductivity, having both wider vessel lumens and larger lumen fractions, and also did not regulate leaf-level transpiration in the drier landscape as efficiently as the two unaffected clones (lower δ¹³C ratios). In turn, one of the healthy growing clones had a completely different hydraulic strategy, having higher wood density, lower lumen fractions, and higher δ¹³C ratios that are widely considered as hydraulically resilient during water stress. The other clone appeared to also gain drought tolerance via higher leaf-level water-use efficiency, although drought tolerance was less clear regarding xylem anatomy. We highlight how variation in relative drought vulnerability can be highly significant even between clones within a single hybrid group. Knowledge of this variation in plant hydraulics between commercially planted and closely related Eucalyptus trees would complement clone deployment programmes in a target landscape.     

Xylem vulnerability to cavitation varies among poplar and willow clones and correlates with yield

Xylem vulnerability to cavitation is a promising criterion for identifying trees with high drought tolerance, but traditional techniques for measuring cavitation resistance are unsuitable for screening large numbers of genotypes. We tested the potential of the new Cavitron technique for high throughput screening of cavitation resistance in five poplar (Populus spp.) and four willow (Salix spp.) clones. The Cavitron technique enabled the screening of three to four clones per day with sufficient accuracy to reveal significant differences between clones. Because intraspecific screening may be better carried out through the identification of correlated and more easily measured traits, we attempted to identify accessible parameters that correlate to cavitation resistance. Variability in vulnerability to cavitation across clones was poorly correlated with anatomical traits such as vessel diameter, vessel wall strength, wood density and fiber wall thickness; however, a striking correlation was established between cavitation resistance and aboveground biomass production, indicating a possible trade-off between xylem safety and growth potential.     

Vessel size and number are contributors to define wood density in cork oak

Cork oak (Quercus suber L.) has a dense wood that allows high-quality uses. In the present work, we study the influence of vessel characteristics, measured through image analysis and optical microscopy, on wood density, measured using X-ray microdensitometry, on 40-year-old trees. Vessel area increases with cambial age (5403–33064 μm²), while wood density decreases (1.229–0.836 g/cm³). The number of vessels is relatively constant at 6 vessels/mm², while vessel proportion in cross-section increases from 3.3% near the pith to 20.5% near the bark. In growth rings closest to the pith, with high wood density and low vessel area, the relationship between the two variables is linear (R ² = −32.1%, P < 0.01) but with increasing tree age and vessel size, the wood density remains rather constant, suggesting that decreases in density might compromise mechanical support of the tree at a stage when the increase in cross-sectional area alone might not provide mechanical stability. Other anatomical characteristics not considered in this study, like large xylem rays that increase with cambial age, may be responsible for the constant density.     

Wood properties of <Emphasis Type="Italic">Pericopsis mooniana</Emphasis> grown in a plantation in Indonesia

The relationships between growth characteristics and wood properties were investigated for a threatened species, Pericopsis mooniana, to promote the establishment of plantations of this species in the tropics. Growth characteristics (diameter and height) and stress-wave velocity (SWV) of trees were measured for 22-year-old P. mooniana trees planted in Indonesia. The trees were categorized into three groups, fast-growing, middle-growing, and slow-growing trees, to investigate the effect of growth rate on the wood properties. In addition, radial variation of anatomical characteristics and wood properties were determined. No significant correlation was found between growth characteristics and SWV. The values for the vessel diameter, cell wall thickness of wood fibers, wood fiber length, basic density, modulus of elasticity, and modulus of rupture from wood at the bark side were higher than those at the pith side. On the other hand, vessel frequency gradually decreased from pith to bark. These results suggested that low-quality wood, such as juvenile wood, existed near the pith area.