74 research outputs found
Recommended from our members
Physical models as an aid for teaching wood anatomy
Student activities and instructor-made models are described to facilitate and encourage other instructors to develop their own appropriate activities and models for teaching the three-dimensional structure of wood.
The teaching activities include making several annual rings with straws pushed into clay, drawing woodâs structure onto a piece of paper that is folded to resemble a wedge, and assigning students to make an anatomical model to present in class. Plans are given for instructor-made models (1:500 scale) of tracheids, vessel elements, and a hardwood âfiberâ to demonstrate their relative dimensions and geometries. These models also include a set of outerwood and corewood tracheids onto which the microfibril angle is traced, and one tracheid on which bordered and cross-field pitting are shown. Plans are then given for a bordered pit pair with its membrane (1:6300 scale). The last model demonstrates the Hagen-Poiseuille equation with an array of 16 conduits that together have the same potential flow as one conduit of two times their diameter. The use of these models has enlivened the classroom and helped students to more readily grasp wood anatomy and function
Recommended from our members
Traits, properties, and performance: how woody plants combine hydraulic and mechanical functions in a cell, tissue, or whole plant
This review presents a framework for evaluating how cells, tissues, organs, and whole plants perform both hydraulic and mechanical functions. The morphological alterations that affect dual functionality are varied: individual cells can have altered morphology; tissues can have altered partitioning to functions or altered cell alignment; and organs and whole plants can differ in their allocation to different tissues, or in the geometric distribution of the tissues they have. A hierarchical model emphasizes that morphological traits influence the hydraulic or mechanical properties; the properties, combined with the plant unit's environment, then influence the performance of that plant unit. As a special case, we discuss the mechanisms by which the proxy property wood density has strong correlations to performance but without direct causality. Traits and properties influence multiple aspects of performance, and there can be mutual compensations such that similar performance occurs. This compensation emphasizes that natural selection acts on, and a plant's viability is determined by, its performance, rather than its contributing traits and properties. Continued research on the relationships among traits, and on their effects on multiple aspects of performance, will help us better predict, manage, and select plant material for success under multiple stresses in the future.This is the publisherâs final pdf. The published article is copyrighted by The Authors and the New Phytologist Trust. It is published by John Wiley & Sons, Inc. The published article can be found at: www.newphytologist.com The New Phytologist Trust is a not-for-profit organization dedicated to the promotion of plant science, facilitating projects from symposia to free access for our Tansley reviews.Keywords: integration, wind, functional trait, tradeoff, drought, biomechanics, xylem anatomy, multiple stressesKeywords: integration, wind, functional trait, tradeoff, drought, biomechanics, xylem anatomy, multiple stresse
Recommended from our members
Do Douglas-fir branches and roots have juvenile wood?
We sampled boles, branches, and roots of four Douglas-fir (Pseudotsuga menziesii var. menziesii) trees to learn a) whether branches and roots have a zone of juvenile wood, defined as a zone with progressive changes in wood density and/or tracheid length from the pith outward at successively greater cambial
ages, and if so, b) whether the radial patterns in branches and roots are similar to those in boles. Samples came from the following positions: bole, 30 cm aboveground; branch, 30 cm outward on the lowest live branch, and root, 1â3 m from the bole. Average sample cambial ages were bole, 60 years; branch, 30
years; and root, 48 years. Roots and branches had higher density wood than did the bole at the positions studied, and roots had the longest tracheids followed by the bole and then the branches. All three positions exhibited juvenile wood but with different radial patterns. All positions had their highest density near the
pith, which was followed by a steep decline in the boles and a more gradual decline in the roots and branches. Boles and roots, but not branches, then showed an increase in density after this decline. Boles and branches had short tracheids near the pith followed by a gradual increase to an asymptotic value. In
contrast, tracheid length in roots was relatively constant from pith to bark, although there was a dip of about 20% from about cambial ages 14 to 24. This study shows that the vascular cambium of this species is not constrained to produce one sole radial pattern of wood properties as it matures. The presence of
different radial patterns in boles, branches, and roots supports the hypothesis that juvenile wood in the bole is an adaptive feature rather than an unavoidable developmental consequence. Further work should investigate more fully the different physiological or mechanical roles of the various wood types within the context of the position in the tree at which they occur.Keywords: root, branch, density, juvenile wood, specific gravity, tracheid length, Douglas-fi
Recommended from our members
Effects of bark thickness estimates on optimal log merchandising
Bark plays a critical role in the life of a tree when it is standing. Once the tree is felled, however, bark has minimal value and
may be a net financial loss to the forest industry. Because of barkâs limited worth, logs are often bought and sold based on under
bark measurements. Removing bark in the forest is generally very difficult, so over bark measurements are often made and
converted to under bark using a bark thickness model. This study investigated the effect of six bark thickness models on the
predicted volume and value recovery obtained during the log bucking process. The results indicate that the type of bark thickness
model used is of lesser importance than obtaining the correct model coefficients. This study investigated the effect of using a bark
thickness model developed for a different species or using data from the same species but a different site. Using the wrong species
coefficients for the chosen model can result in 34 percent of the logs being out-of-specification, volume estimates being incorrect,
and a loss of value to the forest owner of up to 11 percent. The results show that, for the stands in this study, 2 to 5 percent
value gains could be achieved simply by using stand-specific bark thickness coefficients
Recommended from our members
Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in foliar water transport
⢠Hydraulic vulnerability of Douglas-fir (Pseudotsuga menziesii) branchlets
decreases with height, allowing shoots at greater height to maintain hydraulic
conductance (Kshoot) at more negative leaf water potentials (Ψl).
⢠To determine the basis for this trend shoot hydraulic and tracheid anatomical
properties of foliage from the tops of Douglas-fir trees were analysed along a height
gradient from 5 to 55 m.
⢠Values of Ψl at which Kshoot was substantially reduced, declined with height by
0.012 Mpa mâ1. Maximum Kshoot was reduced by 0.082 mmol mâ2 MPaâ1 sâ1 for
every 1 m increase in height. Total tracheid lumen area per needle cross-section,
hydraulic mean diameter of leaf tracheid lumens, total number of tracheids per needle
cross-section and leaf tracheid length decreased with height by 18.4 Îźm2 mâ1,
0.029 Îźm mâ1, 0.42 mâ1 and 5.3 Îźm mâ1, respectively. Tracheid thickness-to-span
ratio (tw/b)2 increased with height by 1.04 Ă 10â3 mâ1 and pit number per tracheid
decreased with height by 0.07 mâ1.
⢠Leaf anatomical adjustments that enhanced the ability to cope with vertical
gradients of increasing xylem tension were attained at the expense of reduced water
transport capacity and efficiency, possibly contributing to height-related decline in
growth of Douglas fir.Keywords: growth limitation, hydraulic conductance, water stress, foliar anatomy, Pseudotsuga menziesii, embolismKeywords: growth limitation, hydraulic conductance, water stress, foliar anatomy, Pseudotsuga menziesii, embolis
Recommended from our members
An Annual Pattern of Native Embolism in Upper Branches of Four Tall Conifer Species
Premise of the study: The Pacific Northwest of North America experiences relatively mild winters and dry summers. For the
tall coniferous trees that grow in this region, we predicted that loss in the hydraulic conductivity of uppermost branches would
be avoided because of difficulty reversing accumulated emboli in xylem that is always under negative pressure.
⢠Methods: To test this hypothesis, we measured native percent loss in hydraulic conductivity (PLC; the decrease of in situ hydraulic
conductivity relative to the maximum) monthly throughout 2009 in branches at the tops (~50 m) of four species in an
old growth forest in southern Washington.
⢠Key results: Contrary to our prediction, freeze â thaw cycles resulted in considerable native PLC. Branches showed hydraulic
recovery in the spring and after a moderate increase in native embolism that was observed after an unusually hot period in
August. The September recovery occurred despite decreases in the leaf and stem water potentials compared to August values.
⢠Conclusions: Recoveries in branches of these trees could not have occurred by raising the water potential enough to dissolve
bubbles simply by transporting water from roots and must have occurred either through water absorption through needles and/
or refilling under negative pressure. Excluding the August value, native embolism values correlated strongly with air temperature
of the preceding 10 d. For three species, we found that branches with lower wood density had higher specific conductivity,
but not greater native PLC than branches with higher wood density, which calls into question whether there is any hydraulic
benefit to higher wood density in small branches in those species.Keywords: Tsuga heterophylla, Abies grandis, wood density, hydraulic conductivity, Thuja plicata, Pseudotsuga menziesi
Recommended from our members
Reduced wood stiffness and strength, and altered stem form, in young antisense 4CL transgenic poplars with reduced lignin contents
⢠Reduced lignin content in perennial crops has been sought as a means to
improve biomass processability for paper and biofuels production, but it is unclear
how this could affect wood properties and tree form.
⢠Here, we studied a nontransgenic control and 14 transgenic events containing
an antisense 4-coumarate:coenzyme A ligase (4CL) to discern the consequences of
lignin reduction in poplar (Populus sp.). During the second year of growth, trees
were grown either free-standing in a field trial or affixed to stakes in a glasshouse.
⢠Reductions in lignin of up to 40% gave comparable losses in wood strength and
stiffness. This occurred despite the fact that low-lignin trees had a similar wood
density and up to three-fold more tension wood. In free-standing and staked trees,
the control line had twice the height for a given diameter as did low-lignin trees.
Staked trees had twice the height for a given diameter as free-standing trees in the
field, but did not differ in wood stiffness.
⢠Variation in tree morphogenesis appears to be governed by lignin ¡ environment
interactions mediated by stresses exerted on developing cells. Therefore our
results underline the importance of field studies for assessing the performance of
transgenic trees with modified wood properties.Keywords: tension wood, lignin, stem form, wood strength, buckling safety factor, transgenic poplar, wood stiffnes
Recommended from our members
Coordination of leaf structure and gas exchange along a height gradient in a tall conifer
The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Ψl) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mmâ2 mâ1, 0.20 mm mâ1, 5.9 Ă 10â3 mm mâ1 and 0.012 mm2 mâ1, respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 Ă 10â2 mm mâ1 and 0.74 Îźm mâ1, respectively. Mesophyll conductance (gm) and CO2 assimilation in ambient [CO2] (Aamb) decreased by 1.1 mmol mâ2 sâ1 per m and 0.082 Îźmol mâ2 sâ1 per m increase in height, respectively. Mean reductions in gm and Aamb of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in Aamb was associated with gm and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar δ13C values with height (0.042â° mâ1) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior.Keywords: leaf anatomy, mesophyll resistance, photosynthesis, growth limitationKeywords: leaf anatomy, mesophyll resistance, photosynthesis, growth limitatio
Recommended from our members
Safety factors for xylem failure by implosion and air-seeding within roots, trunks and branches of young and old conifer trees
The cohesion-tension theory of water transport states that hydrogen bonds hold water molecules together and that they are pulled through the xylem under tension. This tension could cause transport failure in at least two ways: collapse of the conduit walls (implosion), or rupture of the water column through air-seeding. The objective of this research was to elucidate the functional significance of variations in tracheid anatomical features, earlywood to latewood ratios and wood densities with position in young and old Douglas-fir and ponderosa pine trees in terms of their consequences for the safety factors for tracheid implosion and air-seeding. For both species, wood density increased linearly with percent latewood for root, trunk and branch samples. However, the relationships between anatomy and hydraulic function in trunks differed from those in roots and branches. In roots and branches increased hydraulic efficiency was achieved at the cost of increased vulnerability to air-seeding. Mature wood of trunks had earlywood with wide tracheids that optimized water transport and had a high percentage of latewood that optimized structural support. Juvenile wood had higher resistance to air-seeding and cell wall implosion. The two safety factors followed similar axial trends from roots to terminal branches and were similar for both species studied and between juvenile and mature wood.Keywords: tracheid, cell wall, mature wood, juvenile wood, embolism, water transpor
Recommended from our members
Murray's law, the âYarrumâ optimum, and the hydraulic architecture of compound leaves
⢠There are two optima for maximizing hydraulic conductance per vasculature volume in plants. Murray's law (ML) predicts the optimal conduit taper for a fixed change in conduit number across branch ranks. The opposite, the Yarrum optimum (YO), predicts the optimal change in conduit number for a fixed taper.
⢠We derived the solution for YO and then evaluated compliance with both optima within the xylem of compound leaves, where conduits should have a minimal mechanical role. We sampled leaves from temperate ferns, and tropical and temperate angiosperms.
⢠Leaf vasculature exhibited greater agreement with ML than YO. Of the 14 comparisons in 13 species, 12 conformed to ML. The clear tendency towards ML indicates that taper is optimized for a constrained conduit number. Conduit number may be constrained by leaflet number, safety requirements, and the fact that the number of conduits is established before their diameter during development.
⢠Within a leaf, ML compliance requires leafâspecific conductivity to decrease from petiole to petiolule with the decrease in leaf area supplied. A similar scaling applied across species, indicating lower leafâspecific petiole conductivity in smaller leaves. Small leaf size should offset lower conductivity, and petiole conductance (conductivity/length) may be independent of leaf size.Keywords: hydraulic efficiency, wood anatomy, network, leaf specific conductivit
- âŚ