Determination of the hydraulic conductivity of Lamprothamnium by use of the pressure clamp

By use of the pressure-clamp technique, the hydraulic conductivity of the brackish-water alga Lamprothamnium was found to be 5·10^-6 cm s^-1 bar^-1. The dimensions of the internodes are so small that it is possible, for the first time, to measure a complete volume relaxation upon clamping the turgor pressure to a preset value by a feedback control of the pressure probe. As theoretically predicted, the values of the hydraulic conductivity obtained from the initial slope of the volume relaxation induced by the pressure clamp are in agreement (within experimental error) with those obtained from the half-time of the relaxation process. The cell volume also obtained from the analysis of the volume relaxation is the osmotically effective cell volume and is therefore slightly smaller than the value obtained by taking the dimensions of the cell including the cell wall.Abbreviations and symbols Lp hydraulic conductivity - P turgor pressure - S_v initial slope of volume relaxion - T_1/2 half-time of volume relaxation Dedicated to Professor Dr. H. Ziegler on the occasion of his 60th birthday     

Compartment analysis of plant cells by means of turgor pressure relaxation: I. Theoretical considerations

Summary Turgor pressure relaxation curves for individual plant cells represent an important source of information for the plant physiologist. However, the accurate interpretation of these curves is strongly dependent on the model chosen to describe the plant cell. If the compartmentation of the cell into vacuole and cytoplasm is taken into account, a theoretical analysis shows that pressure relaxation curves can be represented by the sum of two exponential functions. Givena priori assumptions about the exchange area of the tonoplast and its reflection coefficient, the hydraulic conductivities of the plasmalemma and tonoplast can be determined and the proportion of the total cell volume occupied by the cytoplasm is also obtained. Numerical solutions to the flow equations have shown that the biphasic nature of pressure relaxations is maintained even when a permeable tonoplast is assumed. Depending on the magnitude of the reflection coefficient and the permeability of the vacuolar membrane, large errors can arise in the determination of the hydraulic conductivity of the tonoplast. However, under certain conditions, even a highly permeable tonoplast may behave like a nonpermeable membrane during pressure relaxation.     

Reliability, repeatability and accuracy of the falling head method for hydraulic conductivity measurements under laboratory conditions

The aim of this study was to verify under lab conditions the reliability, repeatability and accuracy of the falling head method (FHM) for hydraulic conductivity measurements. The FHM is a reliable procedure that has slight variations (less than 10%) in repeated measurements and turns out to be a reliable technique to record the hydraulic conductivities typically described for clogged and unclogged subsurface-flow constructed wetlands (from 4 to ca. 360 m/day). The accuracy of the method is acceptable considering difficulties in the measurement of hydraulic conductivity in highly conductive media. Accordingly, results show measurement deviations of 20% when compared with a laboratory constant head method for highly conductive media (higher than 250 m/day), and 80% for media with low hydraulic conductivity (lower than 50 m/day). The main conclusion of the present paper is that of the FHM is a reliable and repeatable technique for hydraulic conductivity measurements and it is accurate enough for on-site clogging assessment in full-scale constructed wetlands.     

Effects of particulates and lipids on the hydraulic conductivity of Matrigel.

The hydraulic conductivity of a connective tissue is determined both by the fine ultrastructure of the extracellular matrix and the effects of larger particles in the interstitial space. In this study, we explored this relationship by examining the effects of 30- or 90-nm-diameter latex nanospheres or low-density lipoproteins (LDL) on the hydraulic conductivity of Matrigel, a basement membrane matrix. The hydraulic conductivity of Matrigel with latex nanospheres or LDL particles added at 4.8% weight fraction was measured and compared with the hydraulic conductivity of Matrigel alone. The LDL-derived lipids in the gel were visualized by transmission electron microscopy and were seen to have aggregated into particles up to 500 nm in size. The addition of these materials to the medium markedly decreased its hydraulic conductivity, with the LDL-derived lipids having a much larger effect than did the latex nanospheres. Debye-Brinkman theory was used to predict the effect of addition of particles to the hydraulic conductivity of the medium. The theoretical predictions matched well with the results from adding latex nanospheres to the medium. However, LDL decreased hydraulic conductivity much more than was predicted by the theory. The validation of the theoretical model for rigid particles embedded in extracellular matrix suggests that it could be used to make predictions about the influence of particulates (e.g., collagen, elastin, cells) on the hydraulic conductivity of the fine filamentous matrix (the proteoglycans) in connective tissues. In addition, the larger-than-predicted effects of lipidlike particles on hydraulic conductivity may magnify the pathology associated with lipid accumulation, such as in Bruch's membrane of the retina during macular degeneration and the blood vessel wall in atherosclerosis.     

水分浸泡过夜对刺槐枝条最大水分导度测定的影响及年龄差异

枝条最大水分导度是植物水分生理学研究中的核心指标之一，冲洗法是当前用来测定该指标最常用的方法，但在实验测定之前首先必须要找到获得稳定的最大水分导度的可靠方法。本研究中，我们以刺槐（Robinia pseudoacacia L.）不同年龄枝条为实验材料，通过枝条采集后立即用于实验测定和枝条经超纯水中浸泡过夜后再用于实验这两种不同处理方式对不同年龄枝条最大水分导度测定的影响，检测两种处理方式中枝条最大水分导度随冲洗时间的延长是否保持恒定来判断最大水分导度测定值的可靠性，探讨提高枝条最大水分导度测定结果稳定性的有效方法。结果显示：①未浸泡过夜的当年生枝条，经150 kPa压力冲洗达到最大导水率后，继续延长冲洗时间枝条导水率会呈近线性下降，而经超纯水浸泡过夜的当年生枝条以同样实验方法达到最大导水率后，继续延长冲洗时间枝条的导水率基本保持稳定。②二年生枝条无论是否经超纯水浸泡过夜处理，经150 kPa压力冲洗达到最大导水率后枝条的导水率都基本保持稳定，但经超纯水浸泡过夜后，二年生枝条达到最大导水率所需的冲洗时间明显比未浸泡处理短。③根据茎横截面上木质部面积所占百分比和枝条木质密度判断，实验期间当年生枝条的木质化程度明显比二年生枝条低。我们推测未经浸泡过夜的当年生枝条出现木质部水分导度随冲洗时间延长而下降是由于枝条遭受机械性损伤后产生的分泌物在冲洗过程中被引入导管堵塞导管腔所致，而超纯水浸泡枝条过夜可有效降低分泌物被引入导管的可能性。因此，我们认为超纯水浸泡枝条过夜，可提高枝条最大水分导度测定结果的稳定性。     

压力室测定根系导水率方法探讨

用压力室连续测定了玉米根系长压和降压过程的导水率,结果表明,降压过程湍 得的根系导水率显著大于用升压过程的,并且前者的相关系数大于后者,这种差异是由于这两个过程中质外体途径细胞壁空间充水量不同造成的,开始升压时,由于细胞壁空间含水量低,质外体途径阻力大,导致非结构阻力;随着压力的升高,细胞壁空间含水量增大,质外体途径导度增大,减小甚至可以消除非结构阻力,降压法可以使根系快速复水,消除传统方法因长时间复水所致根结构的改变。建议用降压法测定根系导水率。     

Hydraulic conductivity of tonoplast-freeChara cells

Summary This study is the first trial to measure the osmotic water permeability or the hydraulic conductivity of the plasmalemma alone of a plant cell. For this purpose tonoplast-free cells were prepared from intenodal cells ofChara australis and their hydraulic conductivities were measured by the transcellular osmosis method.The transcellular hydraulic conductivity did not change after removing the tonoplast. The transcellular hydraulic conductivity of the tonoplast-free cells was dependent on the internal osmotic pressure as is the case in the tonoplast-containing normal cells. The hydraulic conductivities for both endosmosis and exosmosis of the tonoplast-free cells were equal to respective values of the normal cells. Consequently the ratio between the inward and outward hydraulic conductivities did not change due to the loss of the tonoplast. The results indicate that the resistance of the tonoplast to water flow is negligibly small as compared with that of the plasmalemma and further that the tonoplast is not a factor responsible for the direction-dependency of hydraulic conductivity. The hydraulic conductivity of the plasmalemma is invariable for wide variations of K⁺ and Ca²⁺ in the cytoplasm.     

The bulk hydraulic conductivity of mangrove soil perforated with animal burrows

Flow of groundwater from mangrove swamp sediment to mangrove creeks is likely to be an important pathway in mangrove swamps, particularly for the removal of salt excluded at the mangrove root. The swamps are generally saturated with water, and are perforated with animal burrows, allowing significant groundwater flow to mangrove creeks to occur. The hydraulic conductivity of the sediment is thus an important physical parameter but is very difficult to measure in-situ. In this work, we describe a simple method for determining the hydraulic conductivity of mangrove sediment, including the effect of macropores such as crab burrows, which uses the existing animal burrows as piezometers. Experiments to measure the hydraulic conductivity of the sediment were carried out in a variety of mangrove forests. It was found that hydraulic conductivity varied from around 1 to 10 m per day, which is at least 10 times greater than would be expected if there were no burrows. In order to check the validity of the method, conventional piezometers were used to determine the free water table level in an area of mangroves fringing a creek. From these measurements, hydraulic conductivity was determined independently and found to be consistent with the new methodology.     

A Two Compartment Model Method for Continuous Determination of Hydraulic Parameters of Higher Plant Cells by Pressure Probe Technique

Zhu, G-L. and Lou, C-H. 1988. A two compartment model methodfor continuous determination of hydraulic parameters of higherplant cells by pressure probe technique.—J. exp. BoL 39:961–971. The new model treats the whole measuring system as two compartments:the vacuole and the cavity of the probe, which are connectedby a microcapillary. Instead of a short injection, a continuousinjection of distilled water is used in this model. The mainprinciple of the calculation method is to estimate cell turgorpressure and hydraulic conductivity continuously from the resistanceof the microcapillary and the probe pressure as well as thecurrent flow through the microcapillary. The model avoids theeffect of membrane potential changes on the measurement of hydraulicparameters in pressure steps. In this model, microcapillarieswith a tip diameter smaller than flow rate-limiting dimensionscan be employed. The present method provides a way to monitorcontinuously cell hydraulic conductivity during the pressurerelaxation process with a time resolution in seconds. The calculationis performed automatically using a microcomputer. Key words: Two compartment model, cell pressure probe, computer     

The specific hydraulic conductivity of bovine serum albumin.

Previous studies of extracellular matrix hydraulic conductivity have characterized the flow resistance of glycosaminoglycans, proteoglycans and collagen. This work focuses on serum albumin, present in significant quantities in many connective tissues, but not previously considered for its role in determining connective tissue flow resistance. The specific hydraulic conductivity of bovine serum albumin solutions, as a function of concentration, was calculated from sedimentation and ultrafiltration data available in the literature. A rigid particle hydrodynamic model compared favorably with these results. Experimental measurements on an albumin ultrafiltration cell were in agreement with this model (within experimental error); furthermore, the experimental data confirmed the theoretical prediction that there is no (or negligible) pressure drop through the concentration polarization layer. Use of the hydrodynamic model for albumin specific hydraulic conductivity with literature values for the hindrance of albumin when passing through a glycosaminoglycan (GAG) matrix allows an estimate of the relative importance of the albumin on tissue hydraulic conductivity: in non-cartilaginous tissues with moderate GAG concentrations, tissue levels of albumin can generate flow resistance effects comparable to those of the GAGs, although well less than the flow resistance of these tissues.     

Plant potassium content modifies the effects of arbuscular mycorrhizal symbiosis on root hydraulic properties in maize plants

It is well known that the arbuscular mycorrhizal (AM) symbiosis helps the host plant to overcome several abiotic stresses including drought. One of the mechanisms for this drought tolerance enhancement is the higher water uptake capacity of the mycorrhizal plants. However, the effects of the AM symbiosis on processes regulating root hydraulic properties of the host plant, such as root hydraulic conductivity and plasma membrane aquaporin gene expression, and protein abundance, are not well defined. Since it is known that K(+) status is modified by AM and that it regulates root hydraulic properties, it has been tested how plant K(+) status could modify the effects of the symbiosis on root hydraulic conductivity and plasma membrane aquaporin gene expression and protein abundance, using maize (Zea mays L.) plants and Glomus intraradices as a model. It was observed that the supply of extra K(+) increased root hydraulic conductivity only in AM plants. Also, the different pattern of plasma membrane aquaporin gene expression and protein abundance between AM and non-AM plants changed with the application of extra K(+). Thus, plant K(+) status could be one of the causes of the different observed effects of the AM symbiosis on root hydraulic properties. The present study also highlights the critical importance of AM fungal aquaporins in regulating root hydraulic properties of the host plant.     

Theoretical and experimental exclusion of errors in the determination of the elasticity and water transport parameters of plant cells by the pressure probe technique

The volumetric elastic modulus of the cell wall and the hydraulic conductivity of the cell membranes were measured on ligatured compartments of different sizes of Chara corallina internodes using the pressure probe technique. The ratio between intact cell surface area and the area of puncture in the cell wall and membrane introduced by the microcapillary of the pressure probe was varied over a large range by inserting microcapillaries of widely varying diameters in different sized compartments. The relationship of the elastic modulus and the hydraulic conductivity to turgor pressure was independent of the ratio of intact cell surface area to the area of injury. The increase in the hydraulic conductivity below 2 bar turgor pressure and the volume dependence of the elastic modulus were shown to be the same as those observed in intact nonligatured cells. Theoretical considerations of the possible influence of injury of the cell wall and cell membrane around the inserted microcapillary on the measurement of the water transport and cell wall parameters do not explain the experimental findings. Thus, mechanical artifacts, if at all present, are too small to account for the observed dependence of the hydraulic conductivity and the elastic modulus on turgor pressure. The pressure probe technique thus represents an accurate method for measuring water transport parameters in both giant algal cells and in tissue cells of higher plants.     

Water transport through tall trees: A vertically explicit,analytical model of xylem hydraulic conductance in stems

Trees grow by vertically extending their stems, so accurate stem hydraulic models are fundamental to understanding the hydraulic challenges faced by tall trees. Using a literature survey, we showed that many tree species exhibit continuous vertical variation in hydraulic traits. To examine the effects of this variation on hydraulic function, we developed a spatially explicit, analytical water transport model for stems. Our model allows Huber ratio, stem‐saturated conductivity, pressure at 50% loss of conductivity, leaf area, and transpiration rate to vary continuously along the hydraulic path. Predictions from our model differ from a matric flux potential model parameterized with uniform traits. Analyses show that cavitation is a whole‐stem emergent property resulting from non‐linear pressure‐conductivity feedbacks that, with gravity, cause impaired water transport to accumulate along the path. Because of the compounding effects of vertical trait variation on hydraulic function, growing proportionally more sapwood and building tapered xylem with height, as well as reducing xylem vulnerability only at branch tips while maintaining transport capacity at the stem base, can compensate for these effects. We therefore conclude that the adaptive significance of vertical variation in stem hydraulic traits is to allow trees to grow tall and tolerate operating near their hydraulic limits.     

A new method for the determination of hydraulic conductivity and cell volume of plant cells by pressure clamp

Internodes of Chara corallina were used for experiments in which cell turgor pressure was clamped by means of the pressure probe technique. Essentially, the procedure consisted of a combination of volume and turgor pressure relaxations. This technique permits the determination of the cell volume by nonoptical means. The values obtained are in agreement with the ones determined by optical means. Furthermore, the hydraulic conductivity (L_p) was determined from the initial slope of the volume relaxation; the values thus obtained are in agreement with those calculated from the half-times of pressure relaxations. The determination of L_p from volume relaxation measurements has the advantage that the cell volume, the volumetric elastic modulus of the cell wall, and the internal osmotic pressure do not have to be known. Furthermore, the half-time of volume relaxation is longer than that of pressure relaxation, as shown by theory and experiment. This may be used to enhance the resolution of the relaxation measurement and, thus, to improve the accuracy of L_p determinations for higher plant cells which exhibit a very fast pressure relaxation.     

Xylem cavitation in the leaf of Prunus laurocerasus and its impact on leaf hydraulics

This paper reports how water stress correlates with changes in hydraulic conductivity of stems, leaf midrib, and whole leaves of Prunus laurocerasus. Water stress caused cavitation-induced dysfunction in vessels of P. laurocerasus. Cavitation was detected acoustically by counts of ultrasonic acoustic emissions and by the loss of hydraulic conductivity measured by a vacuum chamber method. Stems and midribs were approximately equally vulnerable to cavitations. Although midribs suffered a 70% loss of hydraulic conductance at leaf water potentials of -1.5 MPa, there was less than a 10% loss of hydraulic conductance in whole leaves. Cutting and sealing the midrib 20 mm from the leaf base caused only a 30% loss of conduction of the whole leaf. A high-pressure flow meter was used to measure conductance of whole leaves and as the leaf was progressively cut back from tip to base. These data were fitted to a model of hydraulic conductance of leaves that explained the above results, i.e. redundancy in hydraulic pathways whereby water can flow around embolized regions in the leaf, makes whole leaves relatively insensitive to significant changes in conductance of the midrib. The onset of cavitation events in P. laurocerasus leaves correlated with the onset of stomatal closure as found recently in studies of other species in our laboratory.     

玉米根系水流导度差异的生理形态原因分析

在人工气候室水培条件下,研究了水分胁迫对不同基因型玉米杂交种及其亲本根系水流导度（Lpr）变化的影响,并从生理和形态角度对其差异进行了分析。结果表明：表型抗旱的杂交种F1代（户单四号）整株根系水流导度最高,具有根系水流导度上的杂种优势现象。对其差异的生理和形态因素分析表明,F1代水流导度高与其高脯氨酸含量、低MDA含量和低质膜透忡有关。同时表明,根系的形态特征对根系的水流导度也存在一定的影响。     

Calcium control of the hydraulic resistance in cells of Chara corallina

Protoplasma - The hydraulic resistance (the reciprocal of the hydraulic conductivity Lp) Lp−1 was measured in cells of Chara corallina by the method of transcellular osmosis. Treatment of...     

Relax and refill: xylem rehydration prior to hydraulic measurements favours embolism repair in stems and generates artificially low PLC values

Diurnal changes in percentage loss of hydraulic conductivity (PLC), with recorded values being higher at midday than on the following morning, have been interpreted as evidence for the occurrence of cycles of xylem conduits' embolism and repair. Recent reports have suggested that diurnal PLC changes might arise as a consequence of an experimental artefact, that is, air entry into xylem conduits upon cutting stems, even if under water, while under substantial tension generated by transpiration. Rehydration procedures prior to hydraulic measurements have been recommended to avoid this artefact. In the present study, we show that xylem rehydration prior to hydraulic measurements might favour xylem refilling and embolism repair, thus leading to PLC values erroneously lower than those actually experienced by transpiring plants. When xylem tension relaxation procedures were performed on stems where refilling mechanisms had been previously inhibited by mechanical (girdling) or chemical (orthovanadate) treatment, PLC values measured in stems cut under native tension were the same as those measured after sample rehydration/relaxation. Our data call for renewed attention to the procedures of sample collection in the field and transport to the laboratory, and suggest that girdling might be a recommendable treatment prior to sample collection for PLC measurements.     

Time Varying Optimization for Monitoring Multiple Contaminants under Uncertain Hydrogeology

This study presents a method for identifying cost effective sampling designs for long-term monitoring of remediation of groundwater over multiple monitoring periods under uncertain flow conditions. A contaminant transport model is used to simulate plume migration under many equally likely stochastic hydraulic conductivity fields and provides representative samples of contaminant concentrations. Monitoring costs are minimized under a constraint to meet an acceptable level of error in the estimation of total mass for multiple contaminants simultaneously over many equiprobable realizations of hydraulic conductivity field. A new myopic heuristic algorithm (MS-ER) that combines a new error-reducing search neighborhood is developed to solve the optimization problem. A simulated annealing algorithm using the error-reducing neighborhood (SA-ER) and a genetic algorithm (GA) are also considered for solving the optimization problem. The method is applied to a hypothetical aquifer where enhanced anaerobic bioremediation of four toxic chlorinated ethene species is modeled using a complex contaminant transport model. The MS-ER algorithm consistently performed better in multiple trials of each algorithm when compared to SA-ER and GA. The best design of MS-ER algorithm produced a savings of nearly 25% in project cost over a conservative sampling plan that uses all possible locations and samples.     

Time Varying Optimization for Monitoring Multiple Contaminants under Uncertain Hydrogeology

This study presents a method for identifying cost effective sampling designs for long-term monitoring of remediation of groundwater over multiple monitoring periods under uncertain flow conditions. A contaminant transport model is used to simulate plume migration under many equally likely stochastic hydraulic conductivity fields and provides representative samples of contaminant concentrations. Monitoring costs are minimized under a constraint to meet an acceptable level of error in the estimation of total mass for multiple contaminants simultaneously over many equiprobable realizations of hydraulic conductivity field. A new myopic heuristic algorithm (MS-ER) that combines a new error-reducing search neighborhood is developed to solve the optimization problem. A simulated annealing algorithm using the error-reducing neighborhood (SA-ER) and a genetic algorithm (GA) are also considered for solving the optimization problem. The method is applied to a hypothetical aquifer where enhanced anaerobic bioremediation of four toxic chlorinated ethene species is modeled using a complex contaminant transport model. The MS-ER algorithm consistently performed better in multiple trials of each algorithm when compared to SA-ER and GA. The best design of MS-ER algorithm produced a savings of nearly 25% in project cost over a conservative sampling plan that uses all possible locations and samples.