Hydraulic and mechanical properties of young Norway spruce clones related to growth and wood structure

Stem segments of eight five-year-old Norway spruce (Picea abies (L.) Karst.) clones differing in growth characteristics were tested for maximum specific hydraulic conductivity (k(s100)), vulnerability to cavitation and behavior under mechanical stress. The vulnerability of the clones to cavitation was assessed by measuring the applied air pressure required to cause 12 and 50% loss of conductivity (Psi(12), Psi(50)) and the percent loss of conductivity at 4 MPa applied air pressure (PLC(4MPa)). The bending strength and stiffness and the axial compression strength and stiffness of the same stem segments were measured to characterize wood mechanical properties. Growth ring width, wood density, latewood percentage, lumen diameter, cell wall thickness, tracheid length and pit dimensions of earlywood cells, spiral grain and microfibril angles were examined to identify structure-function relationships. High k(s100) was strongly and positively related to spiral grain angle, which corresponded positively to tracheid length and pit dimensions. Spiral grain may reduce flow resistance of the bordered pits of the first earlywood tracheids, which are characterized by rounded tips and an equal distribution of pits along the entire length. Wood density was unrelated to hydraulic vulnerability parameters. Traits associated with higher hydraulic vulnerability were long tracheids, high latewood percentage and thick earlywood cell walls. The positive relationship between earlywood cell wall thickness and vulnerability to cavitation suggest that air seeding through the margo of bordered pits may occur in earlywood. There was a positive phenotypic and genotypic relationship between k(s100) and PLC(4MPa), and both parameters were positively related to tree growth rate. Variability in mechanical properties depended mostly on wood density, but also on the amount of compression wood. Accordingly, hydraulic conductivity and mechanical strength or stiffness showed no tradeoff.     

人工兴安落叶松次生木质部的解剖学研究

运用木材解剖图像分析系统和显微照相的方法对人工兴安落叶松次生木质部的解剖结构进行研究,结果表明:落叶松具正常树脂道和受伤树脂道两种类型,前者常见于晚材。落叶松生长轮内的早晚材在干和枝内急变,在根内缓变。早材管胞呈六边形至多边形,胞壁常见单列具缘纹孔,偶见对列具缘纹孔;晚材管胞多呈矩形,胞壁鲜见具缘纹孔,通常为单列具缘纹孔。落叶松木射线同时具有单列木射线和纺锤形木射线两种类型,纺锤形木射线中仅含一枚纵行树脂道。纵行管胞与木射线交叉形成的纹孔场为云杉型。从根到干再到枝,管胞逐渐细化,管胞长度逐渐减小,木射线分布由密到疏。     

杉木管胞具缘纹孔膜超微构造

轴向管胞是针叶材中的主要细胞,它的体积约占木材体积的90%以上,其主要功能是输导水分及强固树体(申宗圻,1984).     

杉木阴沉木的特性

杉木阴沉木的出油率高于现代杉木,其精油检出４２种化合物。与现代杉木的具缘纹孔类型一样,都属于南洋杉Ｂ型,其木块与精油的抗白蚁性,强于现代杉木。杉木阴沉木基部边材耐腐性属耐腐等级、中部边材属稍耐腐等级,对白腐菌耐腐性好,均属耐腐等级,其抗性强于现代杉木。     

Incorporation of transfer resistance between tracheary elements into hydraulic resistance models for tapered conduits

The model of West, Brown and Enquist (1999) shows that hydraulic resistance in trees can be independent of path length, provided that vascular conduits widen sufficiently from tree top to base. We demonstrate that this result does not depend theoretically on branching architecture or cross-sectional conductive area of the stem. Previous studies have shown that pit membrane resistance, encountered when water moves between either tracheids or vessels, accounts for up to 60% of the total resistance in stem segments. When pit membrane resistance, which is neglected by most whole-tree hydraulic models, was incorporated in hydraulic models in three different ways, the near invariance of hydraulic resistance was preserved. If relative pit resistance was independent of tracheid size or if tracheid dimensions were scaled to minimize wood resistivity, the minimum conduit taper required for path length independence equaled that in the original model of West et al. (1999). Under the most realistic model, in which relative pit resistance increased with tracheid radius, this value was doubled. Such taper is not possible within the typical size range of tracheids over the entire length of moderately tall trees, but it might be possible for vessel-bearing trees. Preliminary results indicated that although tracheid radius in the outer growth ring initially increased basipetally from the top of an 18-m tall Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), it stabilized at mid-trunk. Also, conduit taper was not constant in this species, violating a key assumption of the model of West et al. (1999), on which the invariance of hydraulic resistance depends.     

Shoot and root vulnerability to xylem cavitation in four populations of Douglas-fir seedlings

The objectives of this study were to assess the range of genotypic variation in the vulnerability of the shoot and root xylem of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings to water-stress-induced cavitation, and to assess the trade-off between vulnerability to cavitation and conductivity per unit of stem cross-sectional area (k(s)), both within a species and within an individual tree. Douglas-fir occupies a broad range of environments and exhibits considerable genetic variation for growth, morphology, and drought hardiness. We chose two populations from each of two varieties (the coastal var. menziesii and the interior var. glauca) to represent environmental extremes of the species. Vulnerability curves were constructed for shoots and roots by plotting the percentage loss in conductivity versus water potential. Vulnerability in shoot and root xylem varied genetically with source climate. Stem xylem differed in vulnerability to cavitation between populations; the most mesic population, coastal wet (CW), was the most susceptible of the four populations. In the roots, the most vulnerable population was again CW; the interior wet (IW) population was moderately susceptible compared with the two dry populations, coastal dry (CD) and interior dry (ID). Root xylem was more susceptible to cavitation than stem xylem and had significantly greater k(s). The trade-off between vulnerability to cavitation and k(s), however, was not evident across populations. The most vulnerable population (CW) had a shoot k(s) of 0.534 +/- 0.067 &mgr;mol m(-2) s(-1) MPa(-1), compared with 0.734 +/- 0.067 &mgr;mol m(-2) s(-1) MPa(-1) for the less vulnerable CD stems. In the roots, IW was more vulnerable than ID, but had the same k(s).     

Effects of steam explosion on wood appearance and structure of sub-alpine fir

The technology of steam explosion was applied to pre-treat sub-alpine fir (Abies lasiocarpa (Hook.) Nutt.) lumber and to improve its drying characteristics. Effects of steam explosion on the appearance and structure of the lumber are discussed in this paper. The structure of the wood was examined using light microscope (LM) and scanning electron microscope (SEM). The following results were obtained. With increasing temperature, pressure, and explosion cycles the color of the lumber darkened gradually. No significant structural difference between treated and untreated samples was observed using LM when the treatments were carried out at temperatures below 130°C with ten explosion cycles (group A or B). Some fractures were observed in bordered pit pairs between tracheids after 20 explosion cycles at 130°C (group C). More fractures occurred in bordered pit pairs between earlywood tracheids at a temperature of 160°C (group D). More or less fractures in pits between ray parenchyma cells and earlywood tracheids were observed using SEM in all four cases of treatments. Although no change in bordered pits in the tracheid walls between group A and the control group was discovered, groups B, C, and D showed different extents of ruptures in bordered pits, which may lead to break aspirated pits and improve permeability. In these groups, wrinkles and separations in the inner tracheid walls and detachments in middle lamella also occurred and became more serious as temperature or cycles of the treatment increased.     

Hydraulic and anatomical properties of light bands in Norway spruce compression wood

Compression wood (CW), which is formed on the underside of conifer branches, exhibits a lower specific hydraulic conductivity (k(s)) compared with normal wood. However, the first-formed tracheids of an annual ring on the underside of a conifer branch often share several properties with normal tracheids, e.g., thin cell walls and angular cross sections. These first-formed tracheids appear bright when observed by the naked eye and are therefore called light bands (LB). In this study, hydraulic and related anatomical properties of LBs were characterized and compared with typical CW and opposite wood (OW). Measurements were made on branches of Norway spruce (Picea abies (L.) Karst.). Specific hydraulic conductivity was measured with fine cannulas connected to microlitre syringes. Micro- and ultrastructural analysis were performed on transverse and radial longitudinal sections by light and scanning electron microscopy. Xylem areas containing both typical CW and LBs had a k(s) 51.5% that of OW (7.95 +/- 0.97 m(2) s(-1) MPa(-1) x 10(-4)), whereas k(s) of pure CW was only 26.7% that of OW. The k(s) of LBs (6.38 +/- 0.97 m(2) s(-1) MPa(-1) x 10(-4); 80.3% of OW) was estimated from these k(s) values because the cannulas were too wide to measure the k(s) of LBs directly. Mean lumen area of first-formed tracheids on the underside of branches was 65.7% that of first-formed tracheids in OW and about three times that of CW. Light-band tracheids exhibited a bordered pit frequency of 42.7 +/- 1.3 pits mm(-1), which was three times that in CW and 1.6 times that in OW. Bordered pit apertures in LB tracheids (9.15 +/- 0.60 microm(2)) were 1.7 times wider than those in CW and similar in aperture to those in OW. The high k(s) of LBs was correlated with their wide tracheid lumina, high pit frequency and wide pit apertures. We therefore suggest that LBs have a primarily hydraulic function within the mechanically optimized CW region. This might be important for supplying water to living tissues on the underside of branches, as well as to other distal areas along water transport pathways following the spiral grain of wood.     

Xylem cavitation in roots and stems of Douglas-fir and white fir

Roots of hardwoods have been shown to be more vulnerable to xylem cavitation than stems. This study examined whether this pattern is also observed in a conifer species. Vulnerability to cavitation was determined from the pressure required to inject air into the vascular system of hydrated roots and stems, and reduce hydraulic conductance of the xylem. According to the air-seeding hypothesis for the cavitation mechanism, these air pressures predict the negative xylem pressure causing cavitation in dehydrating stems. This was evaluated for stems of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and white fir (Abies concolor (Gord. & Glend.) Lindl.). The air-injection method was applied to roots and stems of different sizes and positions in Douglas-fir trees. Roots, especially smaller roots with a xylem diameter < 5 mm, were more vulnerable to cavitation than stems. Mean cavitation pressure for smaller roots was -2.09 +/- 0.42 versus -3.80 +/- 0.19 MPa for larger roots (> 8 mm diameter). Within the shoot system, smaller stems (< 5 mm diameter) were most vulnerable to cavitation, having a mean cavitation pressure of -4.23 +/- 0.565 versus -5.27 +/- 0.513 MPa for large stems (> 8 mm diameter). There was no correlation between tracheid diameter and mean cavitation pressure within root or stem systems, despite larger tracheid diameters in roots (23.3 +/- 3.9 micro m) than in stems (9.2 +/- 1.6 micro m). Smaller safety margins from cavitation in roots may be beneficial in limiting water use during mild drought, and in protecting the stem from low xylem pressures during extreme drought.     

Anatomical differences in the structural elements of fluid passage of Scots pine sapwood with contrasting treatability

Treatability of wood is a function of anatomical properties developed under certain growing conditions. While Scots pine sapwood material normally is considered as easy to impregnate, great variations in treatability can be observed. In order to study anatomical differences in the structural elements of transverse fluid passage, wood material with contrasting treatability has been compared. Ray composition and resin canal network, membrane areas of fenestriform pits in the cross-field as well as dimension and properties of bordered pits were investigated. The results showed large anatomical differences between the two contrasting treatability groups. Refractory Scots pine sapwood samples developed more rays per mm² tangential section, while they were on average lower in cell numbers than rays found in easily treatable material. Easily treatable material had more parenchyma cells in rays than refractory material. At the same time, a larger membrane area in fenestriform pits in the cross-field was observed in the easily treatable sample fraction. Differences in the composition of resin canal network were not observed. Refractory samples developed on average smaller bordered pit features, with relatively small formed pit apertures compared to the easily treatable samples. In refractory Scots pine sapwood material, the structural elements of fluid passage such as bordered pit dimensions, fenestriform pits in the cross-field and parenchyma cells were altogether developed in smaller dimensions or number. Wood samples from better growing conditions and sufficient water supply showed a better treatability in this study.     

杉木冷冻干燥材和气干材液体浸注性的比较研究

A comparative study was conducted on liquid penetration of the freeze-drying and air-drying sapwood and heartwood lumber of plantation Chinese fir （Cunninghamia lanceolata）. The maximum amount of dyeing solution uptake by the capillary rise method was used to evaluate the liquid penetration properties of the treated wood. The pit aspiration ratio was determined by semithin section method. Changes in wood microstructure were investigated using scanning electron microscopy. The results showed that compared with air drying, the freeze drying had a significant effect on liquid penetration of sapwood and heartwood of Chinese fir. The liquid penetration of sapwood is significantly higher than that of the heartwood for both drying treatments. Low pit aspiration ratio and cracks of pits membrane of some bordered pits are the main reasons for increasing liquid penetration after freeze drying treatment.     

Ultrastructure of pits inPinus banksiana lamb

Summary The cross-sectional view of pitting between various cell types inPinus banksiana Lamb. was studied at the ultrastructural level. Cell types inPinus banksiana include longitudinal tracheids, ray tracheids, ray parenchyma cells, buffer cells and epithelial cells. Two common characteristic features of bordered pit-pairs between longitudinal tracheids are an initial pit border and a thickened torus at the center of the pit membrane. The shape and size of the pit border and torus of bordered pit-pairs between two compression wood cells, and between the last-formed latewood longitudinal tracheid and first-formed earlywood longitudinal tracheid were different from those in the earlywood and latewood longitudinal tracheids. The pit border on the ray tracheid side varied in size and shape due to wall dentation. No initial pit border was found on the pit border of the ray tracheid side. The shape of bordered pit-pairs between two ray tracheids varied considerably due to irregularity of the dentate cell wall. The size of bordered pit-pairs in longitudinal tracheids was between 16 m to 20 m, which was twice the diameter of bordered pit-pairs in ray tracheids. Bordered pitpairs at the end wall of two ray tracheids appeared to be the smallest at 5 m, Pit aspiration occurred in the bordered pit-pairs with or without a torus. In the heartwood zone, some half-borders pit-pairs between tracheary and ray parenchyma cells showed an additional secondary wall on the ray parenchyma cell side. Plasmodesmata were found in the half-bordered pit-pairs as well in the simple pit-pairs. Blind pits were observed between a ray tracheid and a longitudinal tracheid. Bordered pit-pairs between two buffer cells were also observed. The possible functions of buffer cells were discussed.Use of transmission electron microscope provided by the Science Instrumentation Lab, Lakehead University and the technical assistance provided by Mr. A. MacKenzie, Director of Science Instrumentation Lab are gratefully appreciated     

Relations Between Permeability and Structure of Wood

The permeability and the structure of heartwood and sapwood of the solvent-exchange dried and the air-dried green-wood of Chinese-fir(Cunninghamia lanceolata(Lamb.)Hook.)and masson pine(Pinus massoniana Lamb.) were measured in order to study the relations between the permeability and the structure.The results showed that the permeability of sapwood of both the air-dried and the solvent-exchange dried wood was higher than that of heartwood,and the permeability of the solvent-exchanged a bigger number of flow path per unit area of the wood perpendicular to the flow direction resulted from a bigger number of unaspirated pits per unit area and a bigger number of effective pit openings per membrane,and on the other hand,a smaller number of tracheid in series connection per unit length parallel to flow direction resulted from a longer tracheid longth and an effective tracheid length for permeability.     

Tangential pitting in black spruce tracheids

Tangential pit features were studied in a 55-year old black spruce (Picea mariana (Mill) B.S.P.) tree by means of light and electron microscopy.It was found that tangential pitting is lacking from the greatest part of the growth ring, except for the last four tangential rows of latewood tracheids and the first row of early wood tracheids. The average number of pits per tangential wall of a 3.55-mm-long tracheid is 234, 144, 28, 4 and zero, respectively, in the last 5 tangential rows of latewood tracheids, starting at the growth-ring boundary.On the average, tangential pits measure 5.4 m in diameter, possess oval to elliptical apertures, and are randomly distributed uniformly over the tangential tracheid wall. All tangential intertracheid pits are bordered and in that respect are similar to those in the radial walls. Although most of the pits contain membranes with tori, some at the growth-ring boundary lack tori and exhibit randomly oriented microfibrillar structure.     

Microfibril angle non-uniformities within normal and compression wood tracheids

The pattern and extent of variation of microfibril angle (MFA) in normal and compression tracheids of softwood were investigated by using confocal laser scanning microscopy technique. All measurements support the idea that the orientation of microfibrils in single wood tracheids is not uniform. MFA of the radial wall of earlywood tracheids was highly non-uniform and had an approximately circular form of arrangement around the bordered pits (inside the border). Between the bordered pits the measured MFAs were less than the other parts of the tracheid. In the latewood tracheids MFA was less variable. The average orientation of simple pits in the crossfield region was consistent with the mean MFA of the tracheids; however some of the measurements showed a highly variable arrangement in the areas between the simple pits. In many cases the local measured MFAs of compression wood tracheids agreed with the orientation of natural helical cavities of compression wood. Comparing the measured results in different growth rings showed that MFAs in juvenile wood are generally larger than in perfect wood.     

The cellular distribution of lignans in Tsuga heterophylla wood

Summary Western hemlock heartwood contains patches of tracheids with large amounts of cellular inclusions. Microscopic and chemical examination of the wood showed several types of deposits containing the lignans matairesinol, hydroxymatairesinol and conidendrin. The deposits, which were often relatively pure individual lignans, frequently assumed different physical forms and chemical composition. A check in the wood contained three distinct forms of deposits each of which was a different lignan. Rays contained deposits physically similar to those in adjacent tracheids but, while lignans were present in the tracheids, they were not detected in the rays. Lignans lined tracheid walls as surface films and often encrusted the bordered pits. The amount of lignans in the wood was not related to wet wood zones although surface films and pit encrustations should have an influence on physical properties. The location and physical nature of lignan deposits in western hemlock heartwood indicates their biosynthesis has probably taken place at the heartwood periphery in the vicinity of the half-bordered pit.Presented at the International Wood Chemistry Symposium, Seattle, U. S. A. September 1969.Requests for reprints should be sent to W. E. Hillis. We thank Miss J. Barratt for assistance with part of this work and Mr. C. J. Kozlik for collecting wood samples.     

Hydraulic properties of Douglas-fir (Pseudotsuga menziesii) branches and branch halves with reference to compression wood

Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) branch segments were used to test the hypothesis that compression wood reduces xylem transport efficiency. Whole 3-year-old segments were first measured for specific conductivity (k(s), m(2) s(-1) MPa(-1)), then split lengthwise into upper and lower halves, the latter containing all or most of the compression wood in the segment. Halves were then remeasured for k(s) using a new technique that prevents leakage of permeating fluid during measurements. Lower branch halves had significantly lower k(s) than upper halves (6.4 +/- 0.3 versus 9.3 +/- 0.3 m(2) s(-1) MPa(-1) x 10(-4), respectively; n = 36), and despite their larger size, significantly lower hydraulic conductivity (k(h), m(4) s(-1) MPa(-1)) than upper halves. Lower branch halves had higher specific gravity (0.51 +/- 0.01 versus 0.45 +/- 0.01; n = 36), lower water content (123 +/- 2% versus 155 +/- 3%; n = 36), and larger proportions of volume occupied by both cell wall and air than upper halves. Lower halves had more tracheids per annual ring than upper halves (73 +/- 3 versus 63 +/- 2 per radial transect, respectively; n = 36), but tracheids were shorter and had narrower lumens than those of upper branch halves. Differences in hydraulic properties between upper and lower halves suggest that compression wood does reduce xylem transport efficiency. In contrast, the amount of compression wood in each sample did not explain any variation in whole unsplit sample hydraulic properties.     

Hydraulic differences along the water transport system of South American Nothofagus species: do leaves protect the stem functionality?

Hydraulic traits were studied for six Nothofagus species from South America (Argentina and Chile), and for three of these species two populations were studied. The main goal was to determine if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems, consistent with the theory of hydraulic segmentation along the vascular system of trees in ecosystems subject to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density and leaf water relations were examined. Large variations in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency (P(50)) ranged from -0.94 to -2.44 MPa in leaves and from -2.6 to -5.3 MPa in stems across species and populations. Populations in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared with stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance (K(Leaf)) were observed. Both traits were functionally related: species with higher wood density had lower K(Leaf). Other stem and leaf hydraulic traits were functionally coordinated, resulting in Nothofagus species with an efficient delivery of water to the leaves. The integrity of the more expensive woody portion of the water transport pathway can thus be maintained at the expense of the replaceable portion (leaves) of the stem-leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolism formation in the trees more vulnerable to cavitation.     

A model describing axial flow of liquids through conifer wood

Summary A mathematical model has been derived for the prediction of the resistance to viscous liquid flow generated by tracheid lumina and various parts of the bordered pit structure. The model also takes into account changes in pit geometry occurring as the pit membrane deflects when a pressure differential is applied across it. Methods for checking whether flow is truly viscous are presented.Data calculated for Pinus sylvestris suggest that the permeability of earlywood differs markedly from that of latewood; that in latewood the pit apertures contribute significantly to the total resistance to flow; and that kinetic energy corrections to the Poiseuille viscous flow equation may be of some importance at high flow rates.The authors wish to acknowledge the encouragement of Professors Matthews and Roche.     

Anatomical explanations for the changes in properties of western red cedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) wood during heat treatment

Thermal treatment is an alternative to the chemical treatment in wood preservation, which has been used to some extent in improving timber quality. Despite the enormous works done so far on the effects of heat treatment on wood properties, very little is known about the anatomical changes in the various wood species during the process. Wood samples from western red cedar (Thuja plicata) were heat-treated at a temperature of 220°C for 1 and 2 h. The anatomical structures were examined before and after the heat treatment process by using scanning electron microscope (SEM) and related to density, water uptake, thickness swelling and modulus of rupture of wood samples obtained from the same board. Heat treatment of red cedar wood resulted in the destruction of tracheid walls, ray tissues and pit deaspiration. The destroyed tracheid walls and ray tissues appeared to blow up, thus increasing the size of the specimen. The process of pit deaspiration also resulted in increasing size of the pits, thus creating more openings in the wood. These changes in wood anatomy indicate that the well-established chemical degradation is not the only reason for changes in wood properties during heat treatment. However, it is believed that the effects of the chemical changes still outweigh those of the anatomical changes based on the modification observed during the process of heat treatment.