Estimating the equilibrium position by measuring growth stress in weeping branches ofPrunus spachiana Kitamura f.spachiana cv.Plenarosea

The equilibrium position of a current-year branch of the weeping Japanese cherry,Prunus spachiana Kitamura f.spachiana cv.Plenarosea, was estimated by measuring the released strains of growth stresses. In current-year branches that were supported with wires to prevent weeping as soon as the branches first budded, tensile growth stresses on the upper side were smaller than those of the control branches. Gelatinous fibers were rarely found on the upper part of the cross section of the supported branches, whereas the control branches had many gelatinous fibers on the upper part. The upright orientation of the supported branches was closer to the equilibrium position than the weeping orientation of the control branches. The equilibrium position of the branches was thought to be in the initial bud direction, above the horizontal plane; and the weeping style of branch was not the preferred angular orientation forP. spachiana.     

Growth strain in the trunk and branches of Chamaecyparis formosensis and its influence on tree form

Distributions of growth strains in branches, straight trunks and basal sweeping trunks of Chamaecyparis formosensis Matsum. trees were measured with strain gauges. Microfibril angles (MFAs) of the S2 layer of the cell wall were measured by the iodine deposition method and their relationships with growth strain examined. The magnitude of the compressive stress on the lower side of trunks with a basal sweep was greater than that of the tensile stress at the surface of straight trunks. However, transverse compressive stress was similar around the trunk regardless of whether normal wood or compression wood was present. The released surface growth strains varied with MFA. At MFAs of 20-25 degrees , growth stress changed from tension to compression, and compressive stress increased dramatically in the compression wood region. Branches suffer bending stress due to self-loading. This stress is superimposed on the growth stress. Growth strains on the upper or lower sides of branches were larger than those in the trunks, suggesting that generation of growth stress on the lower sides of branches with extensive compression wood is affected by the gravitational bending stress due to self-loading. We conclude that branch form is affected by the interaction between the bending moment due to self-loading and that due to the asymmetric distribution of growth stress. Growth strain distribution in a branch differed depending on whether the branch was horizontal, upward bending or downward bending.     

Tensile growth stress and lignin distribution in the cell walls of black locust (Robinia pseudoacacia)

Seven specimens that contained a continuous gradient of wood from normal to tension wood were collected from an inclined black locust (Robinia pseudoacacia), and the released strain of growth stress was quantified. Lignin distribution in the cell wall was investigated using ultraviolet (UV) microspectrophotometry to examine its relation to the intensity of growth stress. The UV absorption at cell corner middle lamella and in the compound middle lamella remained virtually constant, irrespective of the contractive released strain (i.e., tensile growth stress). The gelatinous (G)-layer began to differentiate, and the UV absorption decreased there in accordance with increases in the contractive released strain. The absorption maximum (max) remained virtually constant at the cell corner middle lamella and in the compound middle lamella at 277–280nm, irrespective of the released strain. The max for the secondary wall of normal wood was 272nm and shifted to 268nm in the G-layer of tension wood as the contractive released strain increased. The percentage of the cross-sectional area, consisting of the G-layer, with respect to the whole cross-sectional area increased with the contractive released strain.     

Stem tangential strain on the tension wood side of <Emphasis Type="Italic">Fagus crenata</Emphasis> saplings

The tangential strain on the inner bark surface of Fagus crenata sapling stems was continuously measured using strain gauges. The total strain increased daily, increasing at night and decreasing during the day. When tension wood was induced by artificial inclination, the strain increased more on the upper side than on the lower side; and the increment in the strain at night was larger on the upper side than on the lower. The change in tangential strain on the inner bark surface arose from changes in the water content and the volume of differentiating cells. Differentiating tension wood fibers appear to contain more water and to expand more at night than differentiating normal wood fibers. We can determine whether tension wood is formed from the tangential strain during growth.     

Formation and structure of reaction wood in Buxus microphylla var. insularis Nakai

Summary Anatomical differences in xylem between the upper and lower sides formed in the inclined stems of Buxus microphylla with different angular displacement from the vertical were examined microscopically. B. microphylla exhibited a pronounced growth promotion on the lower side of the inclined stems. Formation of tension wood (gelatinous fibers) was not observed. Xylem formed on the lower side showed some interesting features resembling the compression wood formed in gymnosperms. The reaction wood tracheids and vessels showed an excessive lignification in their secondary walls but lacked both helical cavities and an S₃ layer, features that were almost the same as those of primitive gymnosperms. These results indicate that B. microphylla has an ability to form compression wood, suggesting that in the genus Buxus a different mechanism in the conducting elements was developed in the phylogenetic evolution.The first author would like to express his sincere thanks to Dr. T. E. Timell, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, for his invaluable suggestions in connection with this research     

Ethylene and tension wood formation in Eucalyptus gomphocephala

Summary Eucalyptus gomphocephala A.DC seedlings grown horizontally for 103 days had less terminal shoot elongation and higher internal and emanated ethylene levels in the basal portion of the stem than seedlings grown vertically under otherwise identical conditions. Horizontal seedlings had greater radial growth in the upper stem half than in the lower half of the basal portion of the stem. Upper halves contained 60–80 percent tension wood by volume, lower halves 0–10 percent tension wood. Radial growth in vertical seedlings was symmetrical, and they contained negligible tension wood. Upper halves of the basal portion of the stem of horizontal seedlings had greater amounts of internal and emanated ethylene than lower halves and vertical seedling halves. Ethylene differences between random halves of vertical seedlings were smaller than differences between upper and lower halves of horizontal seedlings. The data suggest an association between increased ethylene levels and tension wood formation.This work was made possible through the award of a Fulbright Postdoctoral Fellowship and an Honorarium to N. D. Nelson by the Australian-American Educational Foundation and CSIRO Division of Building Research, respectively, and is part of a larger body of research by the authors on hormonal aspects of wood quality in rapidly grown Eucalyptus spp. Appreciation is experssed to Peter Fitzgibbon and Jugo Ilic for competent technical assistance.     

栎木应力木生长偏向性分析

该实验的目的是观察栎木枝条的年轮偏向性和应拉木的显微及化学特性。结果表明,栎木枝桠木髓心偏向上侧,即下侧的生长比上侧迅速。双染色法和SEM的观察发现,胶质层同时发生于枝桠木上下侧的纤维细胞,但上侧的应拉程度比下侧稍显严重。化学分析结果显示,枝桠上下侧的a-纤维素含量仅比正常木高2%~3%,木质素含量仅比正常木低2%~4%。该实验的结论是,栎木枝桠木中反应木同时发生在上下两侧,只是应拉程度有差异,而枝桠木下侧生长迅速造成髓心偏向上侧。     

Reaction wood in Pseudowintera colorata — A vessel-less dicotyledon

Summary Inclined branches of Pseudowintera colorata exhibit pronounced growth promotion to the lower (abaxial) side similar to that found in gymnosperms. The only other significant difference between the anatomy of the upper and lower regions is that the tracheids on the lower side have a larger microfibril angle. Other microscopic features normally associated with compression wood or tension wood are completely absent. The longitudinal shrinkage of samples from the upper and lower regions is shown to be related to the mean microfibril angle in a highly non-linear way, and a relatively small change in microfibril angle is associated with a large change in longitudinal shrinkage. This result is in agreement with the hypothesis that compression wood force generation arises during the lignification phase of secondary wall deposition and is critically dependent on mean microfibril angle.The author is indebted to Mr R. R. Exley of this laboratory who prepared the samples and made all the measurements in this project     

Anatomy and lignin distribution of reaction wood in two Magnolia species

Summary Anatomical features of reaction wood formed in two Magnolia species, M. obovata Thunb. and M. kobus DC. which are considered to be among the primitive angiosperms, were observed. In addition, the distribution of guaiacyl and syringyl units of lignins in the cell walls of normal and reaction wood was examined using ultraviolet (UV)- and visible light (VL)- microspectrophotometry coupled with the Wiesner and M?ule reactions. The two Magnolia species formed a tension-like reaction wood without possessing the typical gelatinous layer (G-layer) on the upper side of the inclined stem or branch, in which a radial growth promotion occurred. Compared with the normal wood, the reaction wood had the following anatomical features: (1) the secondary walls of fiber tracheids lacked the S₃ layer, (2) the innermost layer of fiber-tracheid walls showed a small microfibril angle, a fact being similar to the orientation of the microfibril angle of the G-layer in tension wood, and (3) the amounts of lignin decreased in the cell walls of fiber tracheids, especially with great decrease in proportion of guaiacyl units in lignins. In addition, VL-microspectrophotometry coupled with the Wiesner and M?ule reactions adopted in the present study showed potential to estimate the lignin contents in the cell walls and the proportion of guaiacyl and syringyl units in lignins. Received: 15 July 1998     

Role of the gelatinous layer (G-layer) on the origin of the physical properties of the tension wood of Acer sieboldianum

The tension wood (TW) properties of a 70-year-old specimen of Acer sieboldianum Miq. were analyzed by using the G-fiber model that was proposed in our previous report. The roles of the G-layer on the origins of (1) a high tensile growth stress, (2) a large longitudinal Young’s modulus, and (3) a high longitudinal drying shrinkage in the TW xylem are discussed on the basis of the simulations using the G-fiber model. The results suggest that the G-layer generates a high tensile stress in the longitudinal direction during xylem maturation; the longitudinal Young’s modulus of the green G-layer becomes significantly higher than that of the lignified layer; furthermore, the G-layer tends to shrink extraordinarily more than that of the lignified layer during moisture desorption.This report follows the previous report “Role of the gelatinous layer on the origin of the physical properties of the tension wood.” J Wood Sci (2004) 50:197–208. Part of this paper was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999, and at the 2nd International Conference of the European Society for Wood Mechanics, Stockholm, May 2003This revised version was published online in July 2005. On pages 228–230 the character was replaced by a vertical line.     

Tension wood in aerial roots of ficus benjamina L.

Summary Ficus benjamina L. produces aerial roots from branches. Once anchored in the ground the roots begin secondary growth. They produce tension wood until they have reached a diameter of 4 ... 10 sometimes up to 15 millimeters. From then on normal wood is formed. Roots contract considerably while they are producing tension wood. This can be shown by planting roots in a pot during the free hanging stage. During subsequent contraction they can lift the pot from the ground. Polarizing microscopy, electron microscopy, and x-ray diffraction analysis all indicate that the tension wood of aerial roots is identical in fine structure with tension wood in the upper side of the branches. The fibres of the tension wood possess a very thick unlignified S 2 (G) layer in which the cellulose molecules are arranged almost axially and show a high degree of crystallinity. Preliminary experiments in which auxin paste was applied to taut roots had but a local effect and did not suggest that there was a simple relation between auxin concentration and tension-wood formation.

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Zusammenfassung Freihängende Luftwurzeln von Ficus benjamina L. haben einen Durchmesser von rd. 3 mm. Sobald sie den Boden erreicht und sich in der Erde verankert haben, beginnt ihr Kambium mit dem sekundären Dickenwachstum. Bis zu einem Durchmesser von 4 ... 10, manchmal auch bis 15 mm wird Zugholz, später normales Holz produziert. Die Anlage des Zugholzes wird von einer beträchtlichen Kontraktion der Wurzel begleitet. Wird das untere freihängende Luftwurzelende in einen Topf gepflanzt, so beginnt sofort das sekundäre Dickenwachstum, währenddessen die Kontraktion der Wurzel den Topf vom Boden abhebt. Untersuchungen mit dem Polarisationsmikroskop, dem Elektronenmikroskop sowie röntgenanalytische Untersuchungen zeigten, daß das Zugholz der Luftwurzeln mit dem Zugholz der Astoberseite identisch ist. Zugholzfasern haben eine gut entwickelte S 2 (G) Schicht, in der die Cellulosemoleküle axial gelagert sind und einen hohen Krystallisationsgrad aufweisen. In vorläufigen Untersuchungen wurde Auxinpaste auf gespannte (d. h. Zugholz produzierende) Luftwurzeln gegeben. Der Effekt war jedoch nur ein lokaler und zeigte, daß die Zugholzdifferenzierung nicht in einem einfachen Verhältnis zur Auxinkonzentration steht.

     

The influences of boiling and drying treatments on the behaviors of tension wood with gelatinous layers in <Emphasis Type="Italic">Zelkova serrata</Emphasis>

This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli. These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers.     

Estimation of the shear strength of wood by uniaxial-tension tests of off-axis specimens

To determine shear strength we conducted uniaxial-tension tests of off-axis specimens and examined the proper off-axis angles. Sitka spruce (Picea sitchensis Carr.) and katsura (Cercidiphyllum japonicum Sieb. and Zucc.) were used for the studies. Uniaxial tension tests of the specimens with various off-axis angles were conducted, and the shear stress at failure was obtained. Independent of the tension tests, torsion tests were conducted, and the shear strengths were obtained. Comparing the data of the uniaxial tension and torsion tests, we examined the validity of estimating shear strength by the off-axis tension test. The shear strengths obtained from the tension tests coincided well with those measured by the torsion tests when the specimen had an off-axis angle of 15°–30°. In this off-axis angle range, the tensile stress perpendicular to the grain might have a serious influence on the shear strength, and we thought that the shear strength predicted by uniaxial tension tests should be treated as an approximate value despite the simplicity of the tension test. Other test methods should be adopted to obtain the precise shear strength of wood.     

Mechanical and ecophysiological significance of the form of a young Acer rufinerve tree: vertical gradient in branch mechanical properties

Most tree biomechanics models assume uniformity of mechanical properties within a tree, and only a few studies have focused on differences in mechanical status among branches. We examined mechanical properties of 49 branches of two 10-year-old trees of Acer rufinerve Sieb. et Zucc. For each branch, bending moment due to its own fresh mass, elastic modulus, section modulus and flexural stiffness were obtained. Elastic modulus of the branch was correlated with the density and thickness of the fiber cell wall and decreased with crown depth, indicating that branches at lower positions were more elastic than branches at upper positions. Compared to lower branches, upper branches were less inclined, possessed thicker growth rings, more long shoots and were subject to smaller stresses. The leaf arrangement in the upper branches might be effective in transmitting more light to the lower branches. In contrast, the lower branches were more inclined toward the horizontal and subject to greater stresses than the upper branches. Lower branch inclinations were attributed to smaller dry matter investment in diameter growth. Upper and lower branch inclinations were slightly greater and smaller, respectively, than those predicted by beam theory. The alleviation in inclination of the lower branches is probably caused by negative gravitropic responses such as tension wood formation or upward shoot elongation, or both. The horizontal display of leaves in the lower branches would be effective in light interception. The reduction in cost of the lower branches can be adaptive because they have a shorter life expectancy than the upper branches. The results showed that an adaptive tree form is realized by a vertical gradient in branch mechanical properties.     

On the origin of growth stresses in trees

Summary A mechanism for growth stress generation is studied which involves a contractive strain in the microfibril direction and swelling strain in the transverse direction in the developing wall of wood cells. A cylindrically anisotropic elastic model is used to calculate the accumulation of residual stresses in the S₂ wall as it is formed. An explicit relation between the shrinkage/swelling strains in the growth increment of the cell wall and the resulting axial and circumferential stresses induced in the cell is derived. For gymnosperm cells the transition from tensile stress in normal wood cells to compressive stress in compression wood cells is found with increasing microfibril angle.     

Apical control of branch movements in white pine: Compression wood action

Summary The movements of branches or control stem girdled white pine (Pinus strobus L.) were analyzed using beam theory. The stresses generated in the compression wood (CW) produced bending moments to counter the added bending moments due to new branch growth. The branches on the treated trees produced additional CW after untreated trees stopped elongation and diameter growth. The intensity of the stresses in this additional CW was greater than in the other CW. Thus, branches on treated trees moved up vertically well beyond their initial orientation due to both more CW and more active CW. The branches on untreated trees all deflected downward as branch weight continued to increase after CW production stopped.     

Growth stress distribution in leaning trunks of Cryptomeria japonica

The distribution of growth stresses in leaning trunks of Cryptomeria japonica (L.f.) D. Don was determined by measuring the stresses released by the kerf method with strain gauges glued at specified positions along the trunks. Effects of both tree height and peripheral positions on the surface of leaning trunks on surface growth stress were determined. The inner residual growth strains in leaning trunks were also measured. We found high compression stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However, transverse compression stress was found around the tree trunk in both normal and compression wood. In leaning trees, the distribution of internal stresses in the bent trunk portion differed from that in the erect trunk portion, being compressive on the outside and tensile on the inside. The resistant moment introduced by compression stress generated in compression wood is released by the bending of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We demonstrated that Poisson's effect of longitudinal stresses should be considered when evaluating transverse surface growth stresses. The existence and intensity of compression wood development can be assessed by growth stress measurements. We conclude that the compressing force of compression wood functions physiologically to give an upward righting response in a leaning trunk.     

Effect of pruning on branch production and water relations in widely spaced ponderosa pines

This study dealt with the effects of pruning on branch and leaf area (F _a) production of ponderosa pines growing in silvopastoral systems in Patagonia. We hypothesized that pruning positively influences the number of branches per whorl and their basal area growth rate, changing F _a production. In addition, we studied some water relations in order to explain potential differences in branch growth rates between treatments. Two mathematical models were developed to estimate branch and total F _a. The averaged diameter at the third year of pruning was, for high-pruned trees 3.1 and 3.6 cm at the bottom and middle of the crown, against 4 and 4.4 cm for low-pruned trees. Pruning did not produce changes in the number of branches per whorl (approximately 7.6 branches per whorl). Water stress may be responsible of this lower branch growth in pruned trees. Water potential, stomatal conductance and transpiration were lower in high- than in low-pruned trees.     

银杏树冠结构对主干直径和干形的影响

以19年生实生银杏为研究对象,每木检尺,研究了银杏树冠的结构因子一级侧枝的层性、数量和基径对主干直径和干形的影响,主要结果如下:(1)银杏主干上一级侧枝分布的层性和不均衡,导致了主干不同部位生长量分配的差异,表现为随着树冠高度的增加,一级枝数量在树冠垂直方向上呈现“一年小一年大”的波动式变化;一级侧枝层的层间距在0.58~0.82m之间;某层侧枝数量少时,该层上方的层间距较大,反之亦然。(2)树冠上不同层次的一级侧枝及其数量和基径的差异引起主干直径与材积的不均匀分布,导致树干形质发生变化,表现为一级侧枝的基径随着树冠的高度增加呈现“升高-降低”的变化趋势,且树冠中部的一级侧枝的基径较大;每一轮的侧枝使该层侧枝上部的主干不同程度地变细。随着一级侧枝层的上移,侧枝层使胸高形率呈现缩小的变化趋势。一级侧枝直径生长影响着主干上下部直径增量的分配。     

Effects of phloem girdling in conifers on apical control of branches, growth allocation and air in wood

We investigated effects of stem phloem girdles on apical control of branch angle, stem and branch growth and stem air content in six conifer species. A stem girdle 2 cm above a branch caused the branch to bend upward in all six species. Upward bending was associated with increased formation and action of compression wood (CW) in the lower portion of the branch. Compression wood also formed in the main stem below the branch, suggesting increased auxin production in the branch. A stem girdle 2 cm below a branch (the branch remained directly connected to the apex and distal branches) released the branch from apical control in Tsuga canadensis (L.) Carr., Pinus contorta Dougl. ex Loud. and Pseudotsuga menziesii (Mirb.) Franco. The branch bent up, but there was no CW formation in the stem. In Pinus rigida Mill., the branch exhibited increased cambial activity but did not bend up. A stem girdle > 20 cm below a branch did not release the branch from apical control in any of the species. These results support the hypothesis that branches compete with the subjacent stem for branch-produced photosynthate and that when the branch lacks this competitive sink it is released from apical control. A stem girdle 2 cm below a branch did not cause release of apical control in either Juniperus virginiana L. or Picea abies (L.) Karst. In these species, decreased shoot elongation and cambial activity above the girdle probably prevented release. A stem girdle 2 cm below a branch increased air content in the stem below the girdle in four of five species, whereas the other girdle treatments had no significant effect on stem air content. Although growth was inhibited above the girdle in the two species with the largest increase in air content, growth was not inhibited in the other species. High air content in stem segments isolated from distal auxin and carbohydrate sources is consistent with the hypothesis that a carbohydrate supply is required to refill embolized cells.