Tracheid Lumen Diameter Research Articles

Elevated temperature and CO2 concentration effects on xylem anatomy of Scots pine

We studied the effects of elevated temperature and carbon dioxide concentration ([CO(2)]) alone and together on wood anatomy of 20-year-old Scots pine (Pinus sylvestris L.) trees. The study was conducted in 16 closed chambers, providing a factorial combination of two temperature regimes and two CO(2) concentrations (ambient and elevated), with four trees in each treatment. The climate scenario included a doubling of [CO(2)] and a corresponding increase of 2-6 degrees C in temperature at the site depending on the season. Anatomical characteristics analyzed were annual earlywood, latewood and ring widths, intra-ring wood densities (earlywood, latewood and mean wood density), tracheid width, length, wall thickness, lumen diameter, wall thickness:lumen diameter ratio and mass per unit length (coarseness), and numbers of rays, resin canals and tracheids per xylem cross-sectional area. Elevated [CO(2)] increased ring width in four of six treatment years; earlywood width increased in the first two years and latewood width in the third year. Tracheid walls in both the earlywood and latewood tended to become thicker over the 6-year treatment period when temperature or [CO(2)] was elevated alone, whereas in the combined treatment they tended to become thinner relative to the tracheids of trees grown under ambient conditions. Latewood tracheid lumen diameters were larger in all the treatments relative to ambient conditions over the 6-year period, whereas lumen diameters in earlywood increased only in response to elevated [CO(2)] and were 3-6% smaller in the treatments with elevated temperature than in ambient conditions. Tracheid width, length and coarseness were greater in trees grown in elevated than in ambient temperature. The number of resin canals per mm(2) decreased in the elevated [CO(2)] treatment and increased in the elevated temperature treatments relative to ambient conditions. The treatments decreased the number of rays and tracheids per mm(2) of cross-sectional area, the greatest decrease occurring in the elevated [CO(2)] treatment. It seemed that xylem anatomy was affected more by elevated temperature than by elevated [CO(2)] and that the effects of temperature were confined to the earlywood.

Wood properties of northern forest trees grown under elevated CO<sub>2</sub>, O<sub>3</sub> and temperature

The aim of this study was to investigate the effects of climate change on the radial growth, wood structure and chemistry of silver birch (Betula pendula Roth), trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), sugar maple (Acer saccharum Marsh.) and Norway spruce (Picea abies (L.) Karst.). The materials for this study were obtained from climate change studies carried out in Finland, USA and Sweden. Elevated CO2 concentration, O3 concentration and temperature affected wood properties of the forest trees. In silver birch, elevated CO2 increased ring width and the concentrations of extractives and starch, while the concentrations of cellulose and gravimetric lignin were decreased. The responses to elevated O3 depended on the clone: vessel percentage and nitrogen concentration decreased, while cell wall percentage increased in one clone. In vessel percentage, elevated CO2 ameliorated the O3-induced decrease. Responses of wood properties to elevated CO2 and O3 differed between 3-year-old and 5-year-old aspen and paper birch. In 3-year-old aspen clones and birch, lignin concentration increased under elevated O3. However, elevated CO2 ameliorated the effect, and the lignin response was no longer found with 5-year-old trees. In aspen, elevated CO2 decreased uronic acids and elicited clone-dependent increases in concentrations of extractives and starch. Elevated O3 reduced stem radial growth and vessel lumen diameter, while it increased cell wall thickness in aspen. In 5-year-old paper birch, elevated CO2 increased extractives and decreased starch, while elevated O3 increased both of them. Three-year-old maple was the least responsive of the tree species to both elevated CO2 and O3. In 40-year-old Norway spruce, elevated CO2 decreased nitrogen concentration, earlywood cell wall thickness and tracheid lumen diameter, while ring width in nonfertilised trees and latewood tracheid lumen diameter were increased. Elevated temperature decreased the concentrations of extractives and soluble sugars, and increased cell wall thickness and wood density. The data from these exposure studies shows that wood properties may change as a result of climate change, but the responses to increasing concentrations of CO2 and O3 and to increasing temperature may depend on species and the age of trees. Since trees are longliving organisms, further data on long-term exposure studies are still needed before wood characteristics and material properties for different end-use purposes can be predicted for a future climate.

Transpiration-induced axial and radial tension gradients in trunks of Douglas-fir trees

We determined the axial and radial xylem tension gradients in trunks of young Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Axial specific conductivity (k(s-a)) and sap flux density (Js) were measured at four consecutive depths within the sapwood at a stem height of 1 m. By definition, at a given position in the bole, Js is a function not only of k(s-a) but also of the driving force for water movement. The Js:k(s-a) ratio was therefore used to estimate axial tension gradients and the radial gradients at a stem height of 1 m were calculated from the differences in axial tension gradients at each depth. Tracheid lumen diameter and tracheid length were used to predict differences in k(s-a) and its divergence from the theoretical k(s-a) determined by the Hagen Poisseuille equation. The ratio of k(s-a) (determined in the laboratory) to Js (measured in the field) varied with depth in the sapwood, resulting in non-uniform axial and radial tension gradients from inner to outer sapwood. Transpiration-induced axial tension gradients were in the range of 0.006-0.01 MPa m(-1) excluding the gravitational tension gradient. At a stem height of 1 m, radial tension gradients were in the range of 0.15-0.25 MPa m(-1) and were lower in the middle sapwood than in the inner or outer sapwood. Axial tension gradients were 44-50% higher in the outer sapwood than in the inner sapwood. At a stem height of 1 m, radial Js, calculated on the basis of radial tension gradients and measured radial specific conductivity (k(s-r)), was about two orders of magnitude smaller than axial Js. Our findings indicate that large radial tension gradients occur in the sapwood and clarify the role played by xylem k(s-a) and k(s-r) in determining in situ partitioning of Js in the axial and radial directions.

Effects of branch position on water relations and gas exchange of European larch trees in an alpine community

Water relations and gas exchange were studied in the crowns of small European larch (Larix decidua Mill.) trees with respect to branch position. The upper-crown branches showed significantly higher branch sap flux rate (Fla) and branch conductance (gb) compared to the lower crown (P<0.001). Values of leaf conductance (gl), transpiration rate (E) and net photosynthesis (A), averaged for different ranges of atmospheric vapour pressure deficit (VPD), were also higher in the upper crown position. We suppose that the up to 2.6-fold smaller soil-to-leaf hydraulic conductance observed in the lower branches (P<0.001, compared to upper branches) could contribute to the decreased values of Fla, gb, gl, and E in the lower crown position. Variation in tracheid lumen diameter with respect to crown position (P<0.001) supported the hypothesis that branches growing at the crown base are hydraulically more constrained than branches located at the top of the tree. Leaf area to sapwood area ratio (Ala/Asa) exhibited 1.4 times smaller values in lower crown (P<0.01), however, this could not compensate the effect of decreased hydraulic conductivity of the lower-crown branches.

Genetic parameters of growth and wood quality traits in Picea abies

Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2–0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (<0.2) were found for pulp yield, fibre strength, wood stiffness and wood colour. Lignin content and pulp yield showed low genetic variation, whereas the genotypic coefficient of variation for most other traits ranged between 5 and 15%. Most traits showed low levels of genotype by environment interaction. Among the wood properties, latewood proportion, earlywood density and ring density showed significant, adverse correlations with volume in both clonal trials.

Xylem hydraulic efficiency versus vulnerability in seedlings of four contrasting Mediterranean tree species (Cedrus atlantica, Cupressus sempervirens, Pinus halepensis and Pinus nigra)

We studied the xylem traits and anatomy of four diverse Mediterranean conifers to determine how these species protect themselves against catastrophic xylem failure. Cedrus atlantica, Cupressus sempervirens, Pinus nigra and P. halepensis see- dlings were grown for two years in pots in a greenhouse under well-watered conditions. Measurements were conducted in April and Sep- tember. The vulnerability to cavitation was lower in April in the two pines and cedar whereas the conductivity was lower in the two pines and cypress. There were also large species differences in vulnerability to cavitation in September: loss of 50% conductivity occurred at -2.8 MPa in P. nigra, -3.8 MPa in C. atlantica, -4.8 MPa in C. sempervirens and -4.9 MPa in P. halepensis. Leaf specific conductivity was much higher in Cupressus sempervirens and P. nigra than in Cedrus atlantica and P. halepensis. No trade-off between xylem safety (low vulnerability) and efficiency (high conductivity) was found among the four species. Specific conductivity was directly related to hydraulic mean tracheid lumen diameter, while xylem vulnerability appeared to be independent of tracheid size.

Growth and annual ring structure of Larix sibirica grown at different carbon dioxide concentrations and nutrient supply rates.

We compared effects of ambient (360 vpm) and elevated (720 vpm) carbon dioxide concentration ([CO2]) and high and low nutrient supply rates on stem growth, annual ring structure and tracheid anatomy of Siberian larch (Larix sibirica Ledeb.) seedlings over two growing seasons. Elevated [CO2] had no significant effect on either stem height or diameter growth; however, both stem height and diameter growth were enhanced by the high nutrient supply rate, and these increases were stimulated by elevated [CO2]. Elevated [CO2] tended to increase the width of the annual xylem ring, the number of cells in a radial file spanning the ring, and tracheid lumen diameter, whereas it tended to reduce cell wall thickness, although there were no statistically significant CO2 effects on tracheid anatomy. Changes in tracheid cell morphology seemed to be dependent on changes in shoot elongation rates.

The effects of cambial age and position within the stem on specific conductivity in Douglas-fir ( Pseudotsuga menziesii) sapwood

Specific conductivity (k s, m2s–1MPa–1) describes the permeability of xylem and is determined by all aspects of xylem anatomy that create resistance to the flow of water. Here we test the hypothesis that k s is a function of radial and vertical position within the stem, rather than solely a function of cambial age (ring number from the pith), by measuring k s on samples excised from 35-year-old Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco] trees at six heights and two or three radial positions. Sapwood k s decreased from the cambium to the heartwood boundary, and the difference between outer and inner sapwood increased with height in the tree. Beneath the live crown, inner sapwood had 80–90% the k s of outer sapwood, but only 55% just 10 m higher in the stem (about 10 nodes down from the tree top). Outer sapwood k s peaked near the base of the crown and declined toward both the base and top of the stem. These patterns can be explained by two superimposed effects: the effect of cambial age on the dimensions of tracheids as they are produced, and the effect of xylem aging, which may include accumulation of emboli and aspiration of bordered pits. Tracheid lumen diameter and earlywood and latewood density and width, all factors known to vary with cambial age, were measured on different trees of the same age and from the same stand. Lumen diameter increased with cambial age, whereas the proportion of latewood and growth ring density increased after an initial decrease in the first 5 years. Our results suggest that the effect of cambial age on xylem anatomy is not sufficient to explain variation in k s. Instead, physical position (both vertical and radial) in the stem and cambial age must be considered as determinants of conductivity.

Xylem conductivity and vulnerability to cavitation of ponderosa pine growing in contrasting climates.

We examined the effects of increased transpiration demand on xylem hydraulic conductivity and vulnerability to cavitation of mature ponderosa pine (Pinus ponderosa Laws.) by comparing trees growing in contrasting climates. Previous studies determined that trees growing in warm and dry sites (desert) had half the leaf/sapwood area ratio (A(L)/A(S)) and more than twice the transpiration rate of trees growing in cool and moist sites (montane). We predicted that high transpiration rates would be associated with increased specific hydraulic conductivity (K(S)) and increased resistance to xylem cavitation. Desert trees had 19% higher K(S) than montane trees, primarily because of larger tracheid lumen diameters. Predawn water potential and water potential differences between the soil and the shoot were similar for desert and montane trees, suggesting that differences in tracheid anatomy, and therefore K(S), were caused primarily by temperature and evaporative demand, rather than soil drought. Vulnerability to xylem cavitation did not differ between desert and montane populations. A 50% loss in hydraulic conductivity occurred at water potentials between -2.61 and -2.65 MPa, and vulnerability to xylem cavitation did not vary with stem size. Minimum xylem tensions of desert and montane trees did not drop below -2.05 MPa. Foliage turgor loss point did not differ between climate groups and corresponded to mean minimum xylem tensions in the field. In addition to low A(L)/A(S), high K(S) in desert trees may provide a way to increase tree hydraulic conductivity in response to high evaporative demand and prevent xylem tensions from reaching values that cause catastrophic cavitation. In ponderosa pine, the flexible responses of A(L)/A(S) and K(S) to climate may preclude the existence of significant intraspecific variation in the vulnerability of xylem to cavitation.

Xylem development and hydraulic conductance in sun and shade shoots of grapevine (Vitis vinifera L.): evidence that low light uncouples water transport capacity from leaf area

Morphology, water relations, and xylem anatomy of high-light (sun)- and low-light (shade)-grown Vitis vinifera L. shoots were studied to determine the effects of shading on the hydraulic conductance of the pathway for water flow from the roots to the leaves. Shade shoots developed leaf area ratios (leaf area: plant dry weight) that were nearly threefold greater than sun shoots. Water-potential gradients (ΔΨ·m−1) in the shoot xylem accounted for most of the ΔΨ·m−1 between soil and shoot apex at low and high transpiration rates in both sun and shade shoots, but the gradients were two- to fourfold greater in shade-grown plants. Low light reduced xylem conduit number in petioles, but had an additional slight effect on conduit diameter in internodes. The hydraulic conductance per unit length (Kh) and the specific hydraulic conductivity (ks, i.e. Kh per xylem cross-sectional area) of internodes, leaf petioles, and leaf laminae at different developmental stages leaf plastochron index was calculated from measurements of water potential and water flow in intact plants, from flow through excised organs, and from vessel and tracheid lumen diameters according to Hagen-Poiseuille's equation. For all methods and conductance parameters, the propensity to transport water to sink leaves was severalfold greater in internodes than in petioles. The Kh and ks increased logarithmically until growth ceased, independent of treatment and measurement method, and increased further in pressurized-flow experiments and Hagen-Poiseuille predictions. However, the increase was less in shade internodes than in sun internodes. Mature internodes of shade-grown plants had a two- to fourfold reduced Kh and significantly lower ks than sun internodes. Except very early in development, leaf lamina conductance and ks from shade-grown plants was also reduced. The strong reduction in Kh with only a slight reduction in leaf area (17% of sun shoots) in the shade shoots indicated a decoupling of water-transport capacity from the transpirational surface supplied by that capacity. This decoupling resulted in strongly reduced leaf specific conductivities and Huber values for both internodes and petioles, which may increase the likelihood of cavitation under conditions of high evaporative demand or soil drought.

Relation between the permeability and the anatomy of jack pine sapwood with stand development

The anatomical characteristics of sapwood from the base of the live crown of trees from 11 jack pine stands (Pinusbanksiana Lamb.) of different age and site quality were related to the patterns of change of longitudinal sapwood permeability (k) previously observed to occur among these stands. Tracheid length (Lt) increased rapidly from a minimum of 1.9 mm to a plateau of around 3.6 mm as stand age and site quality (productivity class) increased. Sapwood relative water content (Rs) measured before saturation ranged from 78 to 85% for the majority of trees. Samples taken from trees growing on poor sites, however, exhibited significantly lower values of Rs, which probably resulted in their remaining below saturation during the determination of sapwood permeability. The lower Rs values were assumed to be reflective of more adverse water balances during the growing season associated with rapidly drained and (or) shallow soils. Tracheid lumen diameter (Dl) was positively correlated with k within age-classes 15 and 35, but not thereafter. The initial relation between Dl, and k is thought to be associated with corresponding increases in the area of pit membranes, which determines the number of pores within a pit membrane. Values of k were never more than 60% of the values calculated by Poiseuille's law for ideal capillaries (kc) and were generally less than 40%. Values of k tended to approach kc with increasing Lt and decreasing Dl. Overall, Poiseuille's law by itself could not explain the changes in the hydraulic properties of jack pine sapwood with stand development. However, Lt and Rs could together account for 72% of the variation in k. Young stands that had different k depending on site quality generally had corresponding differences in Lt, Rs, and (or) Dl. Mature stands that had reached maximum k on all quality sites no longer showed differences in Lt, Rs, or Dl.

Photosynthesis and wood structure in Pinus radiata D. Don during dehydration and immediately after rewatering

Abstract. Experiments were carried out on Pinus radiata (D. Don) trees grown as cuttings from clonal parent stock. Some of these trees were about 0.4 m high while others were about 5 m high; all were grown in containers. The stem diameters at the tops and at the bottoms of the large trees, rates of photosynthesis, and needle water potentials were measured both when the trees were well watered and as they dehydrated after water was withheld. The water potentials of well‐watered plants was highest in the small trees and lowest at the top of the large trees. When water was withheld, photosynthesis was in most cases unaffected by a small reduction in water potential, but the rate of photosynthesis fell as water potentials declined further. The stems of the large trees expanded at a constant rate when the trees were well watered and for part of the dehydration period, while subsequent stem shrinkage and the fall in photosynthesis both occurred at approximately the same time.Water potentials increased little in the 24 h after rewatering, and significant rates of photosynthesis were not measured until 2 or 3 d later while renewed stem expansion was not measured until 2 d after rewatering.Water deficits reduced the lumen diameter of newly matured stem tracheids, but increased the thickness of their walls. After 1 month of water potentials of about −2.4 MPa, tracheid lumen diameter and wall thickness were both much reduced, and this reduction continued in tracheids maturing shortly after rewatering.

The relationship between stomatal conductance, transpiration rate and tracheid structure in Pinus radiata clones grown at different water vapour saturation deficits

Abstract. Stomatal conductance and needle water potential of P. radiata clones were measured after 2, 5 and 8 months on plants grown in controlled environment rooms with markedly different water vapour saturation deficits (D). Conductance was significantly lower at high D, but water potential differences between treatments were not significant. When trees were moved between treatments most of the changes in conductances occurred within 2 h, with residual changes after 24 h. Water potentials were not different 24 h after the trees were moved. The effects were completely reversible.Transpiration rates of individual trees were highest in the high D treatment and lowest in the low D treatment. They were not linearly related to D because of decreasing conductance with increasing D.Height growth, diameter growth and foliage areas were not significantly different between treatments. Tracheid lumen diameters tended to be larger in trees grown at higher D although treatment differences were not significant.There were significant clonal differences in shoot conductance and tracheid dimensions.

Control by Indole-3-Acetic Acid of Wood Production in Pinus radiata D. Don Segments in Culture

The effect of indole-3-acetic acid (IAA) on stem radius growth, tracheid lumen diameter, and tracheid wall thickness in P. radiata was investigated. Stem segments from trees that normally produce high-density wood and from trees that normally produce low-density wood were grown in vitro at a number of IAA concentrations between 0 and 20 mg l-1. Maximum increase in stem radius and maximum tracheid lumen diameter were found at IAA concentrations of 6-10 mg l-1. Tracheid wall thickness increased approximately linearly as IAA concentration was increased up to 20 mg l-1. Absolute differences in radial stem increase and in cell lumen diameter between the high- and the low-density stems were greatest at IAA concentrations of 4-10 mg l-1. At low or high IAA concentrations, absolute differences between the clones in their stem radial increase and in their tracheid lumen diameter were small. Proportional differences between the clones in these two factors were greatest at IAA concentrations of 10 mg l-1. Clonal differences in the tracheid wall volume per unit stem volume could account for the differences in wood density only at IAA concentrations of 4-10 mg l-1.