Relationships among xylem transport, biomechanics and storage in stems and roots of nine Rhamnaceae species of the California chaparral

Here, hypotheses about stem and root xylem structure and function were assessed by analyzing xylem in nine chaparral Rhamnaceae species. Traits characterizing xylem transport efficiency and safety, mechanical strength and storage were analyzed using linear regression, principal components analysis and phylogenetic independent contrasts (PICs). Stems showed a strong, positive correlation between xylem mechanical strength (xylem density and modulus of rupture) and xylem transport safety (resistance to cavitation and estimated vessel implosion resistance), and this was supported by PICs. Like stems, greater root cavitation resistance was correlated with greater vessel implosion resistance; however, unlike stems, root cavitation resistance was not correlated with xylem density and modulus of rupture. Also different from stems, roots displayed a trade-off between xylem transport safety from cavitation and xylem transport efficiency. Both stems and roots showed a trade-off between xylem transport safety and xylem storage of water and nutrients, respectively. Stems and roots differ in xylem structural and functional relationships, associated with differences in their local environment (air vs soil) and their primary functions.     

New evidence for large negative xylem pressures and their measurement by the pressure chamber method

Pressure probe measurements have been interpreted as showing that xylem pressures below c. –0.4 MPa do not exist and that pressure chamber measurements of lower negative pressures are invalid. We present new evidence supporting the pressure chamber technique and the existence of xylem pressures well below –0.4 MPa. We deduced xylem pressures in water-stressed stem xylem from the following experiment: (1) loss of hydraulic conductivity in hydrated stem xylem (xylem pressure = atmospheric pressure) was induced by forcing compressed air into intact xylem conduits; (2) loss of hydraulic conductivity from cavitation and embolism in dehydrating stems was measured, and (3) the xylem pressure in dehydrated stems was deduced as being equal and opposite to the air pressure causing the same loss of hydraulic conductivity in hydrated stems. Pressures determined in this way are only valid if cavitation was caused by air entering the xylem conduits (air-seeding). Deduced xylem pressure showed a one-to-one correspondence with pressure chamber measurements for 12 species (woody angiosperms and gymnosperms); data extended to c. –10 MPa. The same correspondence was obtained under field conditions in Betula occidentalis Hook., where pressure differences between air- and water-filled conduits were induced by a combination of in situ xylem water pressure and applied positive air pressure. It is difficult to explain these results if xylem pressures were above –0.4 MPa, if the pressure chamber was inaccurate, and if cavitation occurred by some mechanism other than air-seeding. A probable reason why the pressure probe does not register large negative pressures is that, just as cavitation within the probe limits its calibration to pressures above c. –0.5 MPa, cavitation limits its measurement range in situ.     

华北低山丘陵区常用树种木质部解剖特征及水其力学抗旱性

木本植物木质部解剖特征与水分运输和干旱适应策略密切相关,但目前对华北低山丘陵区常用树种这方面的研究仍然不足。为研究这一地区植物木质部解剖特征与抗旱性的关系,研究以抗旱树种和非抗旱树种各5种为研究对象,通过测定与木质部横截面导管、薄壁组织相关的大量解剖学性状和非结构性碳浓度,比较两类树种木质部解剖特征的差异和解剖性状间的关联,以探究这些树种水力学的干旱适应策略差异。结果显示:1)10个树种的16个木质部性状均有较大变异性;2)两类树种间的平均导管直径和导管密度无显著差异,但抗旱树种导管壁厚度、最大导管直径、旁管薄壁组织比例和轴向薄壁组织比例以及非结构性碳(NSC)浓度显著大于非抗旱树种;3)抗旱树种的导管壁厚度与平均导管直径、最大导管直径和潜在最大导水率均呈显著正相关关系,最大导管直径与潜在最大导水率呈显著正相关关系,但非抗旱树种不存在这些关系。本研究抗旱树种同时具有较大的最大导管直径和较厚的导管壁,在保证较高的水分运输效率的同时又具备一定的抗栓塞能力,较多的旁管薄壁组织和NSC也为抗旱树种提供了更大的木质部水储存和栓塞修复能力。     

The spatial pattern of air seeding thresholds in mature sugar maple trees

Air seeding threshold (P_a) of xylem vessels from current year growth rings were measured along the vertical axis of mature sugar maple trees (Acer saccharum Marsh.), with sampling points in primary leaf veins, petioles, 1-, 3-, and 7-year-old branches, large branches, the trunk and roots. The air seeding threshold was taken as the pressure required to force nitrogen gas through intervessel pit membranes. Although all measurements were made on wood produced in the same year, P_a varied between different regions of A. saccharum, with distal organs such as leaves and petioles having lower P_a than basal regions. Mean (SE) P_a ranged from 1.0 (± 0.1) MPa in primary leaf veins to 4.8 (± 0.1) MPa in the main trunk. Roots exhibited a P_a of 2.8 (± 0.2) MPa, lower than all other regions of the tree except leaf veins and petioles. Mean xylem vessel diameter increased basipetally, with the widest vessels occurring in the trunk and roots. Within the shoot, wider vessels had greater air seeding thresholds, contrasting with trends previously reported. However, further experimentation revealed that differences in P_a between regions of the stem were driven by the presence of primary xylem conduits, rather than differences in vessel diameter. In 1-year-old branches, P_a was significantly lower in primary xylem vessels than in adjacent secondary xylem vessels. This explained the lower values of P_a measured in petioles and leaf veins, which possessed a greater ratio of primary xylem to secondary xylem than other regions. The difference in P_a between primary and secondary xylem was attributed to the greater area of primary cell wall (pit membrane) exposed in primary xylem conduits with helical or annular thickening.     

On-line measurements of K+ activity in the tensile water of the xylem conduit of higher plants

In higher plants the xylem is the main pathway for anti-gravitational, long-distance transport of nutrients and water from the root through the shoot to the upper leaves. In the xylem conduit water is in a metastable state if tension larger than 0.1 MPa (i.e. negative pressure) is developed. While diurnal changes in negative pressure of individual xylem vessels can quite accurately be recorded by the minimal-invasive xylem pressure probe technique and water flow by non-invasive NMR techniques, the problem of continuous monitoring of solute flow remains a hitherto unresolved challenge. As shown here, integration of a K+ selective and a potential measuring microelectrode into the xylem pressure probe allowed on-line measurements of the K+ activity in individual xylem vessels of maize roots together with pressure and trans-root potential, the potential difference between the xylem and the external medium (i.e. the overall driving force of ions through the root tissue). When light irradiation was increased from 10 micro mol m(-2) s(-1) to 300 micro mol m(-2) s(-1) and negative pressure developed in the vessel, xylem K+ activity dropped from 3.6 +/- 2.6 mm to 0.9 +/- 0.7 mm (n = 16), whereas the trans-root potential depolarized from -2 +/- 11 mV to + 12 +/- 11 mV (n = 11), i.e. by + 14 +/- 7 mV. The effect of light on all three parameters was reversible. Exposure of the root to various K+ activities in the bath ranging from 0.1 to 43 mm revealed that the K+ activity of the xylem sap was shielded against short-term fluctuations in K+ supply to a large extent. In contrast, control experiments in which the root was cut 1 cm below the probe insertion point, allowing direct entry of external K+ into the xylem vessels, demonstrated that the xylem equilibrated rapidly with external K+. This was taken simultaneously as a proof for the correct reading of the probe.     

Capacitive effect of cavitation in xylem conduits: results from a dynamic model

Embolisms decrease plant hydraulic conductance and therefore reduce the ability of the xylem to transport water to leaves provided that embolized conduits are not refilled. However, as a xylem conduit is filled with gas during cavitation, water is freed to the transpiration stream and this transiently increases xylem water potential. This capacitive effect of embolism formation on plant function has not been explicitly quantified in the past. A dynamic model is presented that models xylem water potential, xylem sap flow and cavitation, taking into account both the decreasing hydraulic conductance and the water release effect of xylem embolism. The significance of the capacitive effect increases in relation to the decreasing hydraulic conductance effect when transpiration rate is low in relation to the total amount of water in xylem conduits. This ratio is typically large in large trees and during drought.     

Photosynthesis, water use efficiency and stable carbon isotope composition are associated with anatomical properties of leaf and xylem in six poplar species

Although fast‐growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUE_i), stable carbon isotope composition (δ¹³C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUE_i and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUE_i/δ¹³C, whereas P. × euramericana had a considerable growth increment and the highest WUE_i/δ¹³C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (g_s) and lowest WUE_i/δ¹³C. Moreover, significant correlations were observed between WUE_i and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUE_i and δ¹³C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUE_i. It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water‐limited regions and others, e.g. P. cathayana, may be better for water‐abundant areas.     

不同纬度对鹅掌楸次生木质部结构的影响

对生长在北纬23至32度的鹅掌楸（Liriodendron chinense Sarg.）的次生木质部进行了比较解剖学研究。观察的特征有：导管分子的长度、直径、壁厚、梯状穿孔板横闩的数目;导管密度、纤维长度、直径、壁厚;射线的高度、宽度,单列射线的比例,射线的密度等。结果表明,随着纬度的增加,管分子变短变细,壁变薄,梯状穿孔板的横闩数目减少;纤维也变短变线,壁变薄;木射线变敌变窄,单列射线的比例和射线密度增加。     

Radial patterns of xylem sap flow in non-, diffuse- and ring-porous tree species

We investigated radial patterns of sap flux density and wood properties in the sapwood of young loblolly pine (Finns taeda L.), mature white oak (Quercus alba L.) and sweetgum (Liquidambar styraciflua L.), which represent three major classes of wood anatomy: non-porous (coniferous), ring-porous and diffuse-porous. Radial measurements of xylem sap flux density were made in sections of xylem extending to 20 mm and 20–40 mm from the cambium. These measurements were compared with measurements of the relative water content (R_s) and sapwood specific gravity (ρ_r) of corresponding radial sections. In both hardwood species, sap flow differences were rarely significant between the two depth intervals. In pine, a 59% reduction in daily sap flux density from outer to inner sapwood was found. This could not be accounted for by a 3% drop in R_s; rather, an accompanying 9% reduction in ρ_r indicated a transition between the depth intervals from mature to juvenile sapwood, and is the probable cause of the lower flux rate in the inner xylem of pine.     

Wood allocation trade-offs between fiber wall,fiber lumen,and axial parenchyma drive drought resistance in neotropical trees

Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta-analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought-induced mortality. We conclude that strong trade-offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.     

水分和盐分胁迫对番茄植株生长和木质部水力特性的影响

木质部是植株体内水分传输的主要通路,其水力特性的变化会影响植株的水分关系和果实的水分积累。目前关于番茄植株木质部解剖结构和水力特性对水分和盐分胁迫的响应及其与植株生长和果实含水量之间的关系尚不明确。本研究通过日光温室番茄盆栽试验,设置3个处理:对照,土壤含水量(θ)为75%～95%田间持水量(FC),初始电导率(EC)为0.398 dS·m^-1;水分胁迫,开花前θ为75%～95% FC,开花后至成熟期θ为45%～65% FC,EC为0.398 dS·m^-1;盐分胁迫,θ为75%～95% FC,EC为1.680 dS·m^-1,研究了樱桃型番茄(红宝石)和中果型番茄(北番501)植株在水分和盐分胁迫下的植株生长、果实含水量以及木质部水力特性的变化。结果表明: 与对照相比,水分和盐分胁迫下茎秆横截面积和木质部导管直径分别减小了22.0%～40.7%和10.0%～18.3%,茎秆比导水率和桁架柄比导水率分别降低了8.8%～41.1%和12.9%～28.4%,抑制了植株生长,减少了地上部鲜重、果实大小、果实鲜重和含水量,且与樱桃型番茄相比,中果型番茄的降幅更大。此外,果实含水量分别与茎秆和桁架柄比导水率呈显著正相关。综上,番茄植株在水分和盐分胁迫下木质部水力特性指标减小,生长被抑制,果实鲜重显著降低,最终导致产量降低。其中,中果型番茄相较于樱桃型番茄对水分和盐分胁迫更敏感。     

High Molecular Weight Organic Compounds in the Xylem Sap of Mangroves: Implications for Long-Distance Water Transport

The rise of sap in mangroves has puzzled plant physiologists for many decades. The current consensus is that negative pressures in the xylem exist which are sufficiently high to exceed the osmotic pressure of seawater (2.5 MPa). This implies that the radial reflection coefficients of the mangrove roots are equal to unity. However, direct pressure probe measurements in xylem vessels of the roots and stems of mangrove (Rhizophora mangle) grown in the laboratory or in the field yielded below-atmospheric, positive (absolute) pressure values. Slightly negative pressure values were recorded only occasionally. Xylem pressure did not change significantly when the plants were transferred from tap water to solutions containing up to 1700 mOsmol kg^?1 NaCl. This indicates that the radial reflection coefficient of the roots for salt, and therefore the effective osmotic pressure of the external solution, was essentially zero as already reported for other halophytes. The low values of xylem tension measured with the xylem pressure probe were consistent with previously published data obtained using the vacuum/leafy twig technique. Values of xylem tension determined with these two methods were nearly two orders of magnitude smaller than those estimated for mangrove using the pressure chamber technique (?3 to ?6MPa). Xylem pressure probe measurements and staining experiments with alcian blue and other dyes gave strong evidence that the xylem vessels contained viscous, mucilage- and/or protein-related compounds. Production of these compounds resulting from wound or other artifactual reactions was excluded. The very low sap flow rates of about 20–50 cm h^?1 measured in these mangrove plants were consistent with the presence of high molecular weight polymeric substances in the xylem sap. The presence of viscous substances in the xylem sap of mangroves has the following implications for traditional xylem pressure measurement techniques, development of xylem tension, and longdistance water transport: (1) high external balancing pressures in the pressure chamber are needed to force xylem sap to the cut surface of the twig; (2) stable tensions much larger than 0.1 MPa can be developed only occasionally because viscous solutions provide nucleation sites for gas bubble formation; (3) the frequent presence of small gas bubbles in viscous solutions allows water transport by interfacial, gravity-independent streaming at gas/water interfaces and (4) the increased density of viscous solutions creates (gravity-dependent) convectional flows. Density-driven convectional flows and interfacial streaming, but also the very low radial reflection coefficient of the roots to NaCl are apparently the means by which R. mangle maintains water transport to its leaves despite the high salinity of the environment.     

8种木本植物木质部栓塞变化与生理生态指标关系的研究Ⅰ.与植物木质部水势的关系

以自然状况下生长良好的耐旱树种刺槐(Robinia pseudoacacia L.)、元宝枫(Acer truncatum Bge.)、沙棘(Hippophae rhamnoides L.)、白榆(Ulmus pumila L.)、油松(Pinus tabulaeformis Carr.)、白皮松(Pinus bungeana Zucc.ex Endl.)及中生树种女贞(Ligustrum lucidum Ait.)、柳树(Salix matsudana Koidz. f. pendula Schneid.)为研究对象,用压力室法测定木质部水势,用冲洗法测定木质部栓塞程度,研究不同生长季节木质部栓塞与水势间的关系.结果表明针叶树油松、白皮松在各季节水势均较高,水势变化幅度较小,木质部不易发生栓塞,这与其木质部由管胞构成,对木质部栓塞不敏感,在干旱时采用高水势延迟脱水的耐旱策略有关.阔叶树刺槐、元宝枫、沙棘、白榆、女贞和柳树的木质部栓塞现象是其在每天正常生长过程中不可避免的 "平常事件",是它们适应干旱的一种方式.它们的木质部栓塞程度与水势表现出了相反的变化趋势,即同一树种在同一季节内水势值越低,木质部栓塞程度越大,但在不同树种及同一树种的不同季节不存在这种关系.由此可见,植物木质部栓塞对水势的敏感程度(即木质部栓塞脆弱性)主要由树种的木质部结构决定,同时受到树种特性、树木生长发育时期、外界环境因子的影响,木质部栓塞的脆弱性也具有季节变化特征.     

The distribution of xylem hydraulic resistance in the fruiting truss of tomato

The distribution of hydraulic resistances in xylem throughout the pathway leading to the tomato fruit was investigated. Previous work had indicated that there were large resistances within the supporting sections of this pathway (the peduncle and pedicel), perhaps associated with interruptions in the xylem. These high resistances are believed to impede calcium flux into the fruit and thus impair fruit development. It is shown here that fruit on intact plants do not shrink detectably during drought, even when the drought is sufficient to cause marked shrinkage of leaves and visible wilting of the shoot. In explants, it is possible to induce back‐flow from the fruit into the stem (probably via the xylem) but this flow is small and very slow. These observations support the view that there is a large hydraulic resistance in the pathway between fruit and stem. When pulses of water were made available within explants, by scorching of one leaflet, there was a rapid swelling of leaves and sepals. Such rapid fluxes indicate the presence of strong hydraulic (xylem) connections throughout the pathway between leaf and calyx. This shows that there are no significant hydraulic constrictions in the xylem proximal to the calyx. This finding is contrary to some previous conclusions but it is supported by experiments with dyes which showed continuous, functional xylem throughout the peduncle and pedicel. Calculations show that over 90% of the hydraulic resistance between stem and fruit must reside within the fruit pericarp. Implications for calcium nutrition are discussed.     

Intra- and inter-plant variation in xylem cavitation in Betula occidentalis

A modified version of a method that uses positive air pressures to determine the complete cavitation response of a single axis is presented. Application of the method to Betula occidentalis Hook, gave a cavitation response indistinguishable from that obtained by dehydration, thus verifying the technique and providing additional evidence that cavitation under tension occurs by air entry through interconduit pits. Incidentally, this also verified pressure-bomb estimates of xylem tension and confirmed the existence of large (i.e. >0·4 MPa) tensions in xylem, which have been questioned in recent pressure-probe studies. The air injection method was used to investigate variation within and amongst individuals of B. occidentalis. Within an individual, the average cavitation tension increased from 0·66±0·27 MPa in roots (3·9 to 10·7 mm diameter), to 1·17±0·10 MPa in trunks (12 to 16 mm diameter), to 1·36±0·04 MPa in twigs (3·9 to 5 mm diameter). Cavitation tension was negatively correlated with the hydraulically weighted mean of the vessel diameter, and was negatively correlated with the conductance of the xylem per xylem area. Native cavitation was within the range predicted from the measured cavitation response and in situ maximum xylem tensions: roots were significantly cavitated compared with minimal cavitation in trunks and twigs. Leaf turgor pressure declined to zero at the xylem tensions predicted to initiate cavitation in petiole xylem (1·5 MPa). Amongst individuals within B. occidentalis, average cavitation tension in the main axis varied from 0·90 to 1·90 MPa and showed no correlation with vessel diameter. The main axes of juveniles (2–3 years old) had significantly narrower vessel diameters than those of adults, but there was no difference in the average cavitation tension. However, juvenile xylem retained hydraulic conductance to a much higher xylem tension (3·25 MPa) than did adult xylem (2·25 MPa), which could facilitate drought survival during establishment.     

The mechanical behaviour of intracondylar cancellous bone of the femur at different loading rates

The compressive properties of human cancellous bone of the distal intracondylar femur in its wet condition were determined. Specimens were obtained from six cadaveric femora and were tested at a strain rate of 0.002, 0.10 and 9.16 sec⁻¹. It was found that the compressive strength decreases with an increasing vertical distance from the joint. The highest compressive strength level was recorded in the posterior medial condyle. Correlations among the mechanical properties, the bulk specimen density and the bone mineral content yield (i) highly significant correlations between the compressive strength and the elastic modulus (ii) highly significant correlations between the compressive strength or the modulus of elasticity and the bulk specimen density (iii) a doubtful correlation between the compressive strength and the bone mineral content. All recorded graphs of the impact loaded specimens displayed several well defined stress peaks, unlike the graphs recorded at low loading rates. It can be concluded that upon impact loading the localized trabecular failure which is associated with each peak, does not affect the spongy bone's stress capacity in a detrimental way.     

Perfusion of onion root xylem vessels: a method and some evidence of control of the pH of the xylem sap

We describe a method for perfusing the xylem in the stele of excised onion roots with solutions of known composition under a pressure gradient. Tracer studies using [¹⁴C] polyethylene glycol 4000 and the fluorescent dye, Tinopal CBSX, indicated that perfusing solutions passed exclusively through the xylem vessels. The conductance of the xylem was small over the apical 100 mm of the root axis but increased markedly between 100 and 200 mm. Unbuffered perfusion solutions supplied in the range pH 3.7–7.8 emerged after passage through the xylem adjusted to pH 5.2–6.0, indicating the presence of mechanisms for absorbing or releasing protons. This adjustment continued over many hours with net proton fluxes apparently determined by the disparity between the pH of the perfusion solution and the usual xylem sap pH of about 5.5. Mild acidification of the xylem sap by buffered perfusion solutions increased the release of ⁸⁶Rb (K⁺) and ³⁵SO₄ ^2- from the stelar tissue into the xylem stream. The ion-transporting properties of onion roots seemed little changed by excision from the bulbs, or by removal of the apical zones of the root axis. The pH of sap produced by root pressure resembles that found in the outflow solutions of perfused root segments.     

The importance of xylem constraints in the distribution of conifer species

Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (φ₅₀) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi-arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides . Mean φ₅₀ was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of φ₅₀ was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO₂ concentration (c_i) in the leaves of these species during artificial drought was strongly correlated with φ₅₀ suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade-off between xylem conductivity and xylem vulnerability was tested in a sub-sample of four species, but no evidence of an inverse relationship between φ₅₀ and either stem-area specific (K_a) or leaf-area specific conductivity (K₁) was found.     

Diurnal changes in water content of the stems of apple trees, as influenced by irrigation

Abstract Groups of apple trees within an orchard were irrigated by either releasing a fine mist within the canopy or spraying water on the soil. Diurnal changes in the water content of the xylem were inferred from measurements of density made with a gamma probe. Transpiration rates were estimated from leaf temperatures, and water potentials and changes in radial dimension of the stem were recorded. Xylem water content and water potential declined each morning and recovered in the afternoon. Radial dimensions of the xylem followed a similar pattern, but the percentage change was very small in relation to the change in water content of the same tissue. The decline in water content is unlikely to have been caused by cavitation, as it was readily reversed in the afternoon. It is more likely to have been caused by changes in the volume of water occupying already-cavitated fibres or intercellular spaces. Water potential and xylem water content were highest in the mist-irrigated trees and least in the unirrigated controls.     

Physical and mechanical properties of calf lumbosacral trabecular bone.

The physical and mechanical properties of calf lumbar and sacral trabecular bone were determined and compared with those of human trabecular bone. The mean tissue density (1.66 +/- 0.12 g cm-3), equivalent mineral density (169 +/- 36 mg cm-3), apparent density (453 +/- 89 mg cm-3), ash density (194 +/- 59 mg cm-3), ash content (0.6 +/- 0.05%), compressive strength (7.1 +/- 3.0 MPa) and compressive modulus (173 +/- 97 MPa) of calf trabecular bone are similar to those of young human. There were moderate, positive linear correlations between apparent density and equivalent mineral density, ash density, and compressive strength; and between compressive strength and equivalent mineral density (R2 ranging from 0.35 to 0.48, p less than 0.001). Apparent density, ash density, and equivalent mineral density did not differ significantly in different regions. In contrast to humans, the compressive strength increased from posterior, near the facet, to the anterior vertebral body. These comparisons of physical and mechanical properties, as well as anatomical comparisons by others, indicate that the calf spine is a good model of the young non-osteoporotic human spine and thus useful for the testing of spinal instrumentation.