Vessel lengths are important to plant hydraulic studies, but are not often reported because of the time required to obtain measurements. This paper compares the fast dynamic method (air injection method) with the slower but traditional static method (rubber injection method). Our hypothesis was that the dynamic method should yield a larger mean vessel length than the static method. Vessel length was measured by both methods in current year stems of Acer, Populus, Vitis and Quercus representing short‐ to long‐vessel species. The hypothesis was verified. The reason for the consistently larger values of vessel length is because the dynamic method measures air flow rates in cut open vessels. The Hagen–Poiseuille law predicts that the air flow rate should depend on the product of number of cut open vessels times the fourth power of vessel diameter. An argument is advanced that the dynamic method is more appropriate because it measures the length of the vessels that contribute most to hydraulic flow. If all vessels had the same vessel length distribution regardless of diameter, then both methods should yield the same average length. This supports the hypothesis that large‐diameter vessels might be longer than short‐diameter vessels in most species. 相似文献
The objective of this study was to quantify the relationship between vulnerability to cavitation and vessel diameter within a species. We measured vulnerability curves (VCs: percentage loss hydraulic conductivity versus tension) in aspen stems and measured vessel‐size distributions. Measurements were done on seed‐grown, 4‐month‐old aspen (Populus tremuloides Michx) grown in a greenhouse. VCs of stem segments were measured using a centrifuge technique and by a staining technique that allowed a VC to be constructed based on vessel diameter size‐classes (D). Vessel‐based VCs were also fitted to Weibull cumulative distribution functions (CDF), which provided best‐fit values of Weibull CDF constants (c and b) and P50 = the tension causing 50% loss of hydraulic conductivity. We show that P50 = 6.166D?0.3134 (R2 = 0.995) and that b and 1/c are both linear functions of D with R2 > 0.95. The results are discussed in terms of models of VCs based on vessel D size‐classes and in terms of concepts such as the ‘pit area hypothesis’ and vessel pathway redundancy. 相似文献
During vessel evolution in angiosperms, scalariform perforation plates with many slit‐like openings transformed into simple plates with a single circular opening. The transition is hypothesized to have resulted from selection for decreased hydraulic resistance. Previously, additional resistivity of scalariform plates was estimated to be small – generally 10% or less above lumen resistivity – based on numerical and physical models. Here, using the single‐vessel technique, we directly measured the hydraulic resistance of individual xylem vessels. The resistivity of simple‐plated lumens was not significantly different from the Hagen–Poiseuille (HP) prediction (+6 ± 3.3% mean deviation). In the 13 scalariform‐plated species measured, plate resistivity averaged 99 ± 13.7% higher than HP lumen resistivity. Scalariform species also showed higher resistivity than simple species at the whole vessel (+340%) and sapwood (+580%) levels. The strongest predictor of scalariform plate resistance was vessel diameter (r2 = 0.84), followed by plate angle (r2 = 0.60). An equation based on laminar flow through periodic slits predicted single‐vessel measurements reasonably well (r2 = 0.79) and indicated that Baileyan trends in scalariform plate evolution maintain an approximate balance between lumen and plate resistances. In summary, we found scalariform plates of diverse morphology essentially double lumen flow resistance, impeding xylem flow much more than previously estimated. 相似文献
It is well established that transpiration and photosynthetic rates generally increase in resprouting shoots after fire in chaparral shrublands. By contrast, little is known about how plant hydraulic function varies during this same recovery period. We hypothesized that vascular traits, both functional and structural, would also shift in order to support this heightened level of gas exchange and growth. We examined stem xylem‐specific hydraulic conductivity (Ks) and resistance to cavitation (P50) for eight chaparral shrub species as well as several potential xylem structural determinants of hydraulic function and compared established unburned plants and co‐occurring post‐fire resprouting plants. Unburned plants were generally more resistant to cavitation than resprouting plants, but the two groups did not differ in Ks. Resprouting plants had altered vessel structure compared with unburned plants, with resprouting plants having both wider diameter vessels and higher inter‐vessel pit density. For biomechanics, unburned plants had both stronger and denser stem xylem tissue than resprouting plants. Shifts in hydraulic structure and function resulted in resprouting plants being more vulnerable to dehydration. The interaction between time since disturbance (i.e. resprouting versus established stands) and drought may complicate attempts to predict mortality risk of resprouting plants. 相似文献
Dimensions and spatial distribution of vessels are critically important features of woody stems, allowing for adaptation to different environments through their effects on hydraulic efficiency and vulnerability to embolism. Although our understanding of vessel development is poor, basipetal transport of auxin through the cambial zone may play an important role.
Methods
Stems of Populus tremula ×alba were treated with the auxin transport inhibitor N‐1‐naphthylphthalamic acid (NPA) in a longitudinal strip along the length of the lower stem. Vessel lumen diameter, circularity, and length; xylem growth; tension wood area; and hydraulic conductivity before and after a high pressure flush were determined on both NPA‐treated and control plants.
Key Results
NPA‐treated stems formed aberrant vessels that were short, small in diameter, highly clustered, and angular in cross section, whereas xylem formed on the untreated side of the stem contained typical vessels that were similar to those of controls. NPA‐treated stems had reduced specific conductivity relative to controls, but this difference was eliminated by the high‐pressure flush. The control treatment (lanolin + dimethyl sulfoxide) reduced xylem growth and increased tension wood formation, but never produced the aberrant vessel patterning seen in NPA‐treated stems.
Conclusions
These results are consistent with a model of vessel development in which basipetal polar auxin transport through the xylem‐side cambial derivatives is required for proper expansion and patterning of vessels and demonstrate that reduced auxin transport can produce stems with altered stem hydraulic properties. 相似文献
Summary Vessel dimensions (total diameter and length) were determined in tropical and subtropical plants of different growth forms with an emphasis upon lianas (woody vines). The paint infusion and compressed air methods were used on 38 species from 26 genera and 16 families in the most extensive survey of vessel length made to date. Within most stems there was a skewed frequency distribution of vessel lengths and diameter, with many short and narrow vessels and few long and wide ones. The longest vessel found (7.73 m) was in a stem of the liana (woody vine) Pithecoctenium crucigerum. Mean vessel length for 33 species of lianas was 0.38 m, average maximum length was 1.45 m. There was a statistically significant inter-species correlation between maximum vessel length and maximum vessel diameter. Among liana stems and among tree+shrub stems there were statistically significant correlations between stem xylem diameter and vessel dimensions. Lianas with different adaptations for climbing (tendril climbers, twiners, scramblers) were similar in their vessel dimensions except that scramblers tended to have shorter (but not narrower) vessels. Within one genus, Bauhinia, tendril climbing species had greater maximum vessel lengths and diameters than tree and shrub species. The few long and wide vessels of lianas are thought to hydraulically compensate for their narrow stem diameters. The many narrow and short vessels, which are present in the same liana stems, may provide a high resistance auxiliary transport system. 相似文献
Angiosperm hydraulic performance is crucially affected by the diameters of vessels, the water conducting conduits in the wood. Hydraulic optimality models suggest that vessels should widen predictably from stem tip to base, buffering hydrodynamic resistance accruing as stems, and therefore conductive path, increase in length. Data from 257 species (609 samples) show that vessels widen as predicted with distance from the stem apex across angiosperm orders, habits and habitats. Standardising for stem length, vessels are only slightly wider in warm/moist climates and in lianas, showing that, rather than climate or habit, plant size is by far the main driver of global variation in mean vessel diameter. Terminal twig vessels become wider as plant height increases, while vessel density decreases slightly less than expected tip to base. These patterns lead to testable predictions regarding evolutionary strategies allowing plants to minimise carbon costs per unit leaf area even as height increases. 相似文献
Vulnerability curves (VCs) generally can be fitted to the Weibull equation; however, a growing number of VCs appear to be recalcitrant, that is, deviate from a Weibull but seem to fit dual Weibull curves. We hypothesize that dual Weibull curves in Hippophae rhamnoides L. are due to different vessel diameter classes, inter‐vessel hydraulic connections or vessels versus fibre tracheids. We used dye staining techniques, hydraulic measurements and quantitative anatomy measurements to test these hypotheses. The fibres contribute 1.3% of the total stem conductivity, which eliminates the hypothesis that fibre tracheids account for the second Weibull curve. Nevertheless, the staining pattern of vessels and fibre tracheids suggested that fibres might function as a hydraulic bridge between adjacent vessels. We also argue that fibre bridges are safer than vessel‐to‐vessel pits and put forward the concept as a new paradigm. Hence, we tentatively propose that the first Weibull curve may be accounted by vessels connected to each other directly by pit fields, while the second Weibull curve is associated with vessels that are connected almost exclusively by fibre bridges. Further research is needed to test the concept of fibre bridge safety in species that have recalcitrant or normal Weibull curves. 相似文献
Stem xylem features in two evergreen Quercus species (Q. coccifera and Q. ilex) and a deciduous one (Q. faginea) were analysed along an Atlantic-Mediterranean climatic gradient in which rainfall and winter cold experience strong variation.
Mean maximum vessel diameter, vessel density, vessel element length, xylem transverse sectional area, Huber value (xylem transverse
sectional area per leaf area unit), theoretical leaf specific conductivity (estimated hydraulic conductance per leaf area
unit) and total leaf area were determined in 3-year-old branches. Q. faginea presented the widest vessels and the highest theoretical leaf specific conductivity while Q. coccifera showed the lowest total leaf area and the highest Huber value. Studied features did not exhibit significant correlations
with mean minimum January temperature in any species but did show significant relationships with rainfall. In Q. coccifera, mean maximum vessel diameter, vessel element length and theoretical leaf specific conductivity increased with higher rainfall
while vessel density decreased. Mean maximum vessel diameter and total leaf area in Q. ilex increased with precipitation whereas variables of Q. faginea did not show any significant trend. Results suggest that aridity, rather than minimum winter temperature, controls stem xylem
responses in the studied evergreen species. Q. faginea traits did not show any response to precipitation, probably because this species develops deep roots, which in turn makes
edaphic and topographic factors more important in the control of soil water availability. In response to aridity Q. coccifera only exhibits adjustment at a xylem level by reducing its water transport capacity through a reduction of vessel diameter
without changing the amount of xylem tissue or foliage, whereas Q. ilex adjusts its water transport capacity in parallel to the foliage area.
Received: 13 January 1997 / Accepted: 8 April 1997 相似文献
We measured radial variation of carbon isotope composition and vessel traits in tree species in seasonally dry forests of
Northeast Thailand to explore a more reliable and amenable method of tropical dendrochronology for trees that lack visually
detectable and consistent growth rings. Six Dipterocarpaceae species (3 Shorea, 2 Dipterocarpus, and 1 Hopea species) with indistinct or irregular growth rings and teak (Tectona grandis), a species which forms distinct growth rings, were examined. The δ13C value variations in all species showed annual cyclicity. Dipterocarpaceae species usually marked the lowest values of δ13C in the middle of the growing season, whereas teak had the lowest values at nearly the end of the growing season. Since the
growing season of the species examined almost corresponds to the rainy season in the study area, the δ13C variation was likely caused by the change in moisture availability. The different variation pattern of teak was attributable
to its stronger dependence on 13C-enriched reserved material early in the growing season. Changes in tree vessel traits for all species examined also showed
annual cyclicity. Dipterocarpaceae species showed significant correlation between δ13C values and vessel measurements. Vessel lumen (mean area, tangential and radial diameter, and proportion of total area) had
a negative correlation, whereas vessel frequency showed a positive correlation. The correlations indicated that changes in
vessel traits were caused by the seasonal variation of moisture available to the trees. Thus, we concluded that methods using
wood anatomy, as well as δ13C, have great potential for use as tools in tropical dendrochronology within the context of seasonal climate. 相似文献
Objective: Obesity is linked with large vessel atherosclerosis and diabetes. Its association with microvascular changes is less clear. We investigated the associations among retinal vessel diameters, vessel wall signs, and BMI in an older population. Research Methods and Procedures: Retinal photographs were taken on 3654 persons aged 49+ years at baseline of the Blue Mountains Eye Study in Australia. Arteriolar and venular diameters were measured from digitized retinal photographs of the right eyes. BMI was calculated as weight (kilograms)/height (meters2). Incident obesity was defined in persons with BMI ≤ 30 at baseline but >30 after 5 years. A significant weight gain was defined as an increase in BMI of 2+ SDs (4 or more units) over the 5‐year period. Results: At baseline, mean BMI was 26.1 (±4.6) in this population. At 5‐year examinations, 177 (10.0% of 1773 at risk) developed incident obesity, and 136 (6.4% of 2143 at risk) had significant weight gain. After adjusting for age, sex, smoking, triglyceride levels, and mean arterial blood pressure, persons with wider retinal venular diameters had a higher risk of incident obesity (odds ratio, 1.8; 95% confidence interval, 1.0 to 3.1, comparing the highest with lowest venular diameter quintiles) and significant weight gain (odds ratio, 1.7; 95% confidence interval, 0.9 to 3.2). These associations were attenuated with further adjustment for baseline BMI. Arteriolar diameter was unrelated with baseline or change in BMI. Discussion: Wider retinal venular diameter is associated with risk of obesity, independent of hypertension, diabetes, lipids, and cigarette smoking. These data may support a role for impaired microvascular function in the course of weight gain. 相似文献
This study addressed the hypothesis that phylogenetic changes in plant size at reproductive maturity may have facilitated adaptive radiation of Geonoma species within rain forest understory habitats. Leaf size, leaf form, plant size, and growth form were compared within and among 23 species of Geonoma from lowland and montane rain forest areas of Costa Rica and Colombia. Leaf size was significantly correlated with crown height in 18 of the 21 species examined, and with stem diameter in 17 of the species. In species characterized by a gradual ontogenetic transition from bifid to dissected leaves, shoots with bifid leaves were significantly smaller than shoots with dissected leaves with respect to rachis length, number of plications, and stem diameter. Among species, stem diameter below the crown explained 74% of the variation in leaf size (rachis length). Crown height and stem diameter were positively correlated among clustered species, but not among solitary species or all species combined. Leaf dissection was correlated with crown height among the 17 species with dissected leaves; species with bifid leaves were significantly smaller than species with dissected leaves with respect to leaf size and stem diameter. Solitary species had larger leaves and larger stem diameters than clustered species at the same crown heights. Morphological patterns among species generally followed within-species trends. These patterns suggest that Geonoma species are variants on a generic theme:within and among species, leaf size and complexity of form increase with stem diameter and crown height. Solitary and clustered growth forms appear to be morphologically convergent; within each of these architectural groups, the generic theme still applies. Evolutionary changes in leaf size, leaf form, and plant size, however, have clearly involved other factors in addition to variation in plant size. 相似文献
Xylem vessels transition through different stages during their functional lifespan, including expansion and development of vessel elements, transition to vessel hydraulic functionality, and eventual transition to post‐functionality. We used information on vessel development and function to develop a model of vessel lifespan for woody plants.
Methods
We examined vessel functional lifespan using repeated anatomical sampling throughout the growing season, combined with active‐xylem staining to evaluate vessel hydraulic transport functionality. These data were combined with a literature review. The transitions between vessel functional lifespans for several species are illustrated, including grapevine (Vitis vinifera L., Vitaceae), English oak (Quercus robur L., Fagaceae), American chestnut [Castanea dentata (Marshall) Borkh.; Fagaceae], and several arid and semi‐arid shrub species.
Key Results
In intact woody plants, development and maturation of vessel elements may be gradual. Once hydraulically functional, vessel elements connect to form a vessel network that is responsible for bulk hydraulic flow through the xylem. Vessels become nonfunctional due to the formation of gas emboli. In some species and under some conditions, vessel functionality of embolized conduits may be restored through refilling. Blockages, such as tyloses, gels, or gums, indicate permanent losses in hydraulic functional capacity; however, there may be some interesting exceptions to permanent loss of functionality for gel‐based blockages.
Conclusions
The gradual development and maturation of vessel elements in woody plants, variation in the onset of functionality between different populations of vessels throughout the growing season, and differences in the timing of vessel transitions to post‐functionality are important aspects of plant hydraulic function. 相似文献
Spatial patterns in vessel diameter, vessel density and xylem conducting efficiency within a crown were examined in closed-canopy
trees of silver birch (Betula pendula). The variation in anatomical and hydraulic characteristics of branches was considered from three perspectives: vertically
within a crown (lower, middle and upper crown), radially along main branches (proximal, middle and distal part), and with
respect to branch orders (first-, second- and third-order branches). Hydraulically weighted mean diameter of vessels (Dh) and theoretical specific conductivity of the xylem (kt) exhibited no vertical trend within the tree crown, whereas leaf-specific conductivity of the xylem (LSCt) decreased acropetally. Variation in LSCt was governed by sapwood area to leaf area ratio (Huber value) rather than by changes in xylem anatomy. The acropetal increase
in soil-to-leaf conductance (GT) within the birch canopy is attributable to longer path length within the lower-crown branches and higher hydraulic resistance
of the shade leaves. Dh, kt and LSCt decreased, while vessel density (VD) and relative area of vessel lumina (VA) increased distally along main branches. A strong
negative relationship between vessel diameter and VD implies a trade-off between hydraulic efficiency and mechanical stability
of xylem. Dh and VD combined explained 85.4% of the total variation of kt in the regression model applied to the whole data set. Xylem in fast-growing branches (primary branches) had greater area
of vessel lumina per unit cross-sectional area of sapwood, resulting in a positive relationship between branch radial growth
rate and kt. Dh, kt and LSCt decreased, whereas VD increased with increasing branch order. This pattern promotes the hydraulic dominance of primary branches
over the secondary branches and their dominance over tertiary branches. In this way crown architecture contributes to preferential
water flow along the main axes, potentially providing better water supply for the branch apical bud and foliage located in
the outer, better-insolated part of the crown. 相似文献
Stereotactic biopsy is used to enable diagnostic confirmation of brain tumors and treatment planning. Despite being a well‐established technique, it is related to significant morbidity and mortality rates mostly caused by hemorrhages due to blood vessel ruptures. This paper presents a method of vessel detection during stereotactic biopsy that can be easily implemented by integrating two side‐view fibers into a conventional side‐cutting biopsy needle. Tissue within the needle window is illuminated through the first fiber; the second fiber detects the remitted light. By taking the ratio of the intensities at two wavelengths with strongly differing hemoglobin absorption, blood vessels can be recognized immediately before biopsy sampling. Via ray tracing simulations and phantom experiments, the dependency of the remission ratio R = I578/I650 on various parameters (blood oxygenation, fiber‐to‐vessel and inter‐fiber distance, vessel diameter and orientation) was investigated for a bare‐fiber probe. Up to 800–1200 µm away from the probe, a vessel can be recognized by a considerable reduction of the remission ratio from the background level. The technique was also successfully tested with a real biopsy needle probe on both optical phantoms and ex‐vivo porcine brain tissue, thus showing potential to improve the safety of stereotactic biopsy.
Dual‐wavelength remission measurement for the detection of blood vessels during stereotactic biopsy. 相似文献
The relationship of selected wood anatomical characters of NepaleseRhododendron with stem diameter, plant height, altitude, and plant form was investigated. We studied one to three specimens each of 26
species: five species each of trees and subtrees I, three species of subtrees II, and 13 species of shrubs. Multiple regression
analysis and actual distribution of character values show that pore characters and multiseriate ray ratio have a stronger
correlation with stem diameter than altitude; that pore density, vessel element length, fiber-tracheid length, and multiseriate
ray density and width are equally related to altitude and stem diameter, or to altitude and plant height; and that bar number,
and multiseriate ray area and height have a stronger connection with altitude. Among the characters, average pore area is
most strongly correlated with stem diameter and increases exponentially as diameter increases. For wood structure of NepaleseRhododendron, 17 to 63 % of the variation is affected by non-anatomical factors. The general trends in wood structure of NepaleseRhododendron show that trees and subtrees form one continuous unit whereas shrubs form another that often has wider ranges of variation. 相似文献
Within-species and within-stem variation in vessel diameter and total vessel length were examined using the latex paint method on six species of tropical and subtropical lianas (woody vines). Narrow vessels were almost always rather short, but wide vessels ranged from short to long. Within Pithecoctenium crucigerum, larger diameter stems tended to have longer as well as wider vessels, with a maximum vessel length and width of 6.25 m and 366 μm, respectively. Within stems of Saritaea magnifica, P. crucigerum, Hippocratea volubilis, and Vitis rotundifolia, narrow vessels had lower mean, median, and maximum vessel lengths than wide vessels. Vessels with intermediate diameters tended to have intermediate lengths. In Stigmaphyllon ellipticum and Bauhinia fassoglensis the outer system of secondary xylem tended to have longer as well as wider vessels than the inner system. Those narrow vessels (<50 μm) that did occur in the outer system were short (<0.20 m), and were similar in length and diameter to those of the inner system. 相似文献