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Soil Interface (soil + interface)
Selected AbstractsThe cyclic nucleotide-gated channel, AtCNGC10, influences salt tolerance in ArabidopsisPHYSIOLOGIA PLANTARUM, Issue 3 2008Kun-Mei Guo Cyclic nucleotide-gated channels (CNGCs) in the plasma membrane transport K+ and other cations; however, their roles in the response and adaptation of plants to environmental salinity are unclear. Growth, cation contents, salt tolerance and K+ fluxes were assessed in wild-type and two AtCNGC10 antisense lines (A2 and A3) of Arabidopsis thaliana (L.) Heynh. Compared with the wild-type, mature plants of both antisense lines had altered K+ and Na+ concentrations in shoots and were more sensitive to salt stress, as assessed by biomass and Chl fluorescence. The shoots of A2 and A3 plants contained higher Na+ concentrations and significantly higher Na+/K+ ratios compared with wild-type, whereas roots contained higher K+ concentrations and lower Na+/K+ ratios. Four-day-old seedlings of both antisense lines exposed to salt stress had smaller Na+/K+ ratios and longer roots than the wild-type. Under sudden salt treatment, the Na+ efflux was higher and the K+ efflux was smaller in the antisense lines, indicating that AtCNGC10 might function as a channel providing Na+ influx and K+ efflux at the root/soil interface. We conclude that the AtCNGC10 channel is involved in Na+ and K+ transport during cation uptake in roots and in long-distance transport, such as phloem loading and/or xylem retrieval. Mature A2 and A3 plants became more salt sensitive than wild-type plants because of impaired photosynthesis induced by a higher Na+ concentration in the leaves. [source] Response of unbounded soil in scaled boundary finite-element methodEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002John P. Wolf Abstract The scaled boundary finite-element method is a powerful semi-analytical computational procedure to calculate the dynamic stiffness of the unbounded soil at the structure,soil interface. This permits the analysis of dynamic soil,structure interaction using the substructure method. The response in the neighbouring soil can also be determined analytically. The method is extended to calculate numerically the response throughout the unbounded soil including the far field. The three-dimensional vector-wave equation of elasto-dynamics is addressed. The radiation condition at infinity is satisfied exactly. By solving an eigenvalue problem, the high-frequency limit of the dynamic stiffness is constructed to be positive definite. However, a direct determination using impedances is also possible. Solving two first-order ordinary differential equations numerically permits the radiation condition and the boundary condition of the structure,soil interface to be satisfied sequentially, leading to the displacements in the unbounded soil. A generalization to viscoelastic material using the correspondence principle is straightforward. Alternatively, the displacements can also be calculated analytically in the far field. Good agreement of displacements along the free surface and below a prism foundation embedded in a half-space with the results of the boundary-element method is observed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Ascomycetes associated with ectomycorrhizas: molecular diversity and ecology with particular reference to the HelotialesENVIRONMENTAL MICROBIOLOGY, Issue 12 2009Leho Tedersoo Summary Mycorrhizosphere microbes enhance functioning of the plant,soil interface, but little is known of their ecology. This study aims to characterize the ascomycete communities associated with ectomycorrhizas in two Tasmanian wet sclerophyll forests. We hypothesize that both the phyto- and mycobiont, mantle type, soil microbiotope and geographical distance affect the diversity and occurrence of the associated ascomycetes. Using the culture-independent rDNA sequence analysis, we demonstrate a high diversity of these fungi on different hosts and habitats. Plant host has the strongest effect on the occurrence of the dominant species and community composition of ectomycorrhiza-associated fungi. Root endophytes, soil saprobes, myco-, phyto- and entomopathogens contribute to the ectomycorrhiza-associated ascomycete community. Taxonomically these Ascomycota mostly belong to the orders Helotiales, Hypocreales, Chaetothyriales and Sordariales. Members of Helotiales from both Tasmania and the Northern Hemisphere are phylogenetically closely related to root endophytes and ericoid mycorrhizal fungi, suggesting their strong ecological and evolutionary links. Ectomycorrhizal mycobionts from Australia and the Northern Hemisphere are taxonomically unrelated to each other and phylogenetically distant to other helotialean root-associated fungi, indicating independent evolution. The ubiquity and diversity of the secondary root-associated fungi should be considered in studies of mycorrhizal communities to avoid overestimating the richness of true symbionts. [source] The exopolysaccharide of Rhizobium sp.ENVIRONMENTAL MICROBIOLOGY, Issue 8 2008Brassica napus roots but contributes to root colonization, YAS34 is not necessary for biofilm formation on Arabidopsis thaliana Summary Microbial exopolysaccharides (EPSs) play key roles in plant,microbe interactions, such as biofilm formation on plant roots and legume nodulation by rhizobia. Here, we focused on the function of an EPS produced by Rhizobium sp. YAS34 in the colonization and biofilm formation on non-legume plant roots (Arabidopsis thaliana and Brassica napus). Using random transposon mutagenesis, we isolated an EPS-deficient mutant of strain YAS34 impaired in a glycosyltransferase gene (gta). Wild type and mutant strains were tagged with a plasmid-born GFP and, for the first time, the EPS produced by the wild-type strain was seen in the rhizosphere using selective carbohydrate probing with a fluorescent lectin and confocal laser-scanning microscopy. We show for the fist time that Rhizobium forms biofilms on roots of non-legumes, independently of the EPS synthesis. When produced by strain YAS34 wild type, EPS is targeted at specific parts of the plant root system. Nutrient fluctuations, root exudates and bacterial growth phase can account for such a production pattern. The EPS synthesis in Rhizobium sp. YAS34 is not essential for biofilm formation on roots, but is critical to colonization of the basal part of the root system and increasing the stability of root-adhering soil. Thus, in Rhizobium sp. YAS34 and non-legume interactions, microbial EPS is implicated in root,soil interface, root colonization, but not in biofilm formation. [source] Hillslope hydrology and wetland response of two small zero-order boreal catchments on the Precambrian ShieldHYDROLOGICAL PROCESSES, Issue 22 2007M. D. Frisbee Abstract Two Precambrian Shield zero-order catchments were monitored from January 2003 to July 2004 to characterize their hydrological and biogeochemical characteristics prior to a forest management experiment. Hydrometric observations were used to examine temporal trends in hillslope-wetland connectivity and the hillslope runoff processes that control wetland event response. The hillslope groundwater flux from the longer transect (E1) was continuous throughout the study period. Groundwater fluxes from a shorter and steeper hillslope (E0) were intermittent during the study period. Large depression storage elements (termed micro-basins) located on the upper hillslope of the E1 catchment appeared to be at least partly responsible for the observed rapid wetland runoff responses. These micro-basins were hydrologically connected to a downslope wetland by a subsurface channel of glacial cobbles that functioned as a macropore channel during episodic runoff events. The runoff response from the hilltop micro-basins is controlled by antecedent water table position and water is quickly piped to the wetland fringe through the cobble channel during high water table conditions. During periods of low water table position, seepage along the bedrock,soil interface from the hilltop micro-basin and other hillslopes maintained hillslope,wetland connectivity. The micro-basins create a dynamic variable source-area runoff system where the contributing area expands downslope during episodic runoff events. The micro-basins occupied 30% of the E1 catchment and are a common feature on the Precambrian Shield. Copyright © 2007 John Wiley & Sons, Ltd. [source] A conceptual model of preferential flow systems in forested hillslopes: evidence of self-organizationHYDROLOGICAL PROCESSES, Issue 10 2001Roy C. Sidle Abstract Preferential flow paths are known to be important conduits of subsurface stormflow in forest hillslopes. Earlier research on preferential flow paths focused on vertical transport; however, lateral transport is also evident in steep forested slopes underlain by bedrock or till. Macropores consisting of decayed and live roots, subsurface erosion, surface bedrock fractures, and animal burrows form the basis of a ,backbone' for lateral preferential flow in such sites. Evidence from field studies in Japan indicates that although individual macropore segments are generally <0·5 m in length, they have a tendency to self-organize into larger preferential flow systems as sites become wetter. Staining tests show clear evidence of interconnected macropore flow segments, including: flow within decayed root channels and subsurface erosion cavities; flow in small depressions of the bedrock substrate; fracture flow in weathered bedrock; exchange between macropores and mesopores; and flow at the organic horizon,mineral soil interface and in buried pockets of organic material and loose soil. Here we develop a three-dimensional model for preferential flow systems based on distributed attributes of macropores and potential connecting nodes (e.g. zones of loose soil and buried organic matter). We postulate that the spatially variable and non-linear preferential flow response observed at our Japan field site, as well as at other sites, is attributed to discrete segments of macropores connecting at various nodes within the regolith. Each node is activated by local soil water conditions and is influenced strongly by soil depth, permeability, pore size, organic matter distribution, surface and substrate topography, and possibly momentum dissipation. This study represents the first attempt to characterize the spatially distributed nature of preferential flow paths at the hillslope scale and presents strong evidence that these networks exhibit complex system behaviour. Copyright © 2001 John Wiley & Sons, Ltd. [source] Numerical analysis of the response of battered piles to inclined pullout loadsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2009Hussein Mroueh Abstract This paper presents a three-dimensional finite element analysis of the response of battered piles to the combined lateral and vertical pullout loads. Analyses are carried out using an elastoplastic constitutive law based on the non-associated Mohr,Coulomb criterion. The influence of the contact condition at the pile,soil interface is also investigated. Analyses show that the load's inclination with regard to the pile's axis affects both the lateral and axial response of the battered piles. Analyses also show that the pullout capacity of battered piles is affected by the pile's inclination regarding the vertical axis as well as the load's inclination regarding the pile's axis. The investigation of the influence of the contact condition at the soil,pile interface shows that the possibility of sliding at the soil,pile interface affects the response of battered piles subjected to loads with low inclination regarding the pile's axis. Copyright © 2008 John Wiley & Sons, Ltd. [source] Inextensible reinforcement on non-linear elasto-plastic subgrade under oblique pullINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 18 2008J. T. Shahu Abstract In this paper, a rational analysis of pullout resistance of inextensible sheet reinforcement subjected to oblique end force has been presented considering a non-linear (hyperbolic), elasto-plastic, normal stress,displacement relationship of the subgrade. Under an oblique pull, high normal stresses develop on stronger subgrades, thus mobilizing high shearing resistance at the reinforcement,soil interface. The higher the bearing resistance of the subgrade, the higher the horizontal component of pullout force and the lower the end displacement of the reinforcement. On the other hand, the end displacement at pullout can become very high for weaker subgrades especially at high values of the angle of obliquity. Also, the pullout capacity under oblique loading for weaker subgrades may approach or even fall below the axial pullout capacity at high values of the angle of obliquity. These adverse pullout responses owing to a low value of bearing resistance of subgrade are magnified when the subgrade stiffness is also small. On weaker subgrades, improvement in angle of interface shear is not advisable as this leads to further reduction in the pullout force and increase in the end displacement. Results are compared with back analysis of published test data on model reinforced soil walls. The comparison suggests that the present model leads to a more rational and better prediction of the pullout failure. Copyright © 2008 John Wiley & Sons, Ltd. [source] The modelling of anchors using the material point methodINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2005C. J. Coetzee Abstract The ultimate capacity of anchors is determined using the material point method (MPM). MPM is a so-called meshless method capable of modelling large displacements, deformations and contact between different bodies. A short introduction to MPM is given and the derivation of the discrete governing equations. The analysis of a vertically loaded anchor and one loaded at 45° is presented. The load,displacement curves are compared to that obtained from experiments and the effect of soil stiffness and anchor roughness is investigated. The results of the vertically loaded anchor are also compared to an analytical solution. The displacement of the soil surface above the anchor was measured and compared to the numerical predictions. Convergence with mesh refinement is demonstrated and the effect of mesh size and dilatancy angle on the shear band width and orientation is indicated. The results show that MPM can model anchor pull out successfully. No special interface elements are needed to model the anchor,soil interface and the predicted ultimate capacities were within 10% of the measured values. Copyright © 2005 John Wiley & Sons, Ltd. [source] Measurement of plane-wave spectra of ground penetrating radar antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2005H. R. Lenler-Eriksen Abstract The plane-wave transmitting spectrum (PWTS) of a ground-penetrating radar (GPR) loop antenna close to the air,soil interface is measured by means of a probe buried in soil. Probe correction is implemented based upon knowledge about the complex permittivity of the soil and the current distribution of the probe. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 215,216, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20591 [source] Detection of subsurface permafrost features with ground-penetrating radar, Barrow, AlaskaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2001K. M. Hinkel Abstract A ground-penetrating radar (GPR) survey was conducted in May 1999 on the 1 km2 Circumpolar Active Layer Monitoring (CALM) grid 5 km east of Barrow, Alaska. Spatially continuous measurements were collected along established transects while the active layer remained frozen. The primary objectives were to determine the ,long-term' position of the permafrost table, to recognize ice wedges and ice lenses, and to locate the organic,mineral soil interface. GPR signal and core collection were performed in tandem to verify signal interpretation, to calibrate the instrument, and to determine optimal GPR data-collection parameters. Two-way travel times from the antenna to subsurface reflectors were compared with measured depths obtained from soil cores to estimate an average pulse propagation velocity of 0.13 m/ns through the frozen soil. The most conspicuous subsurface reflectors were ice wedges, which gave high-amplitude hyperbolic reflections. Owing to its higher ice content, the approximate long-term position of the permafrost table could be traced laterally across the profile. Radar interpretations were obscured by the effects of cryoturbation, and because some horizons lack sufficient contrast in electrical properties. Highly detailed information can be obtained by collecting radar data at relatively slow speeds of advance, by using faster scanning rates (>32 scans/s), and by employing high-frequency antennas (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd. RÉSUMÉ Un levé réalisé avec un radar dont les ondes pénètrent dans le sol a été réalisé en mai 1999 sur un km2 appartenant à la grille établie pour suivre l'évolution de la couche active circumpolaire (CALM), 5 km a l'est de Barrow, Alaska. Des mesures ont été réalisées le long de transects alors que la couche active était gelée. Les premiers objectifs étaient de déterminer la position à long terme de la table du pergélisol, de reconnaître les coins et les lentilles de glace, et de localiser le contact entre les sols organiques et minéraux. Les données radar et des carottes de sondages ont été recueillies au même moment pour vérifier l'interprétation des données radar, calibrer l'instrument et déterminer les meilleurs paramètres d'enregistrement. Deux facons de calculer les temps de parcours depuis l'antenne jusqu'aux réflecteurs souterrains ont été comparés avec des mesures obtenues par sondages, pour estimer une vitesse moyenne de propagation de 0.13 m/ns à travers le sol gelé. Les réflecteurs les plus apparents ont été les coins de glace qui donnent des réflexions hyperboliques de grande amplitude. En raison de leur haute teneur en glace, la position approximative à long terme de la table du pergélisol a pu être reconnue le long des profils. Les interprétations sont obscurcies par les effects des cryoturbations et aussi, parce que certains horizons n'ont pas un contraste suffisant dans leurs propriétés électriques. Une information hautement détaillée peut être obtenue par la méthode radar en utilisant des vitesses lentes d'avancée, de rapides vitesses de scannages (>32 scans/s) et en utilisant des antennes de hautes fréquence (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd. [source] Crops and genotypes differ in efficiency of potassium uptake and usePHYSIOLOGIA PLANTARUM, Issue 4 2008Zed Rengel Cultivars with increased efficiency of uptake and utilization of soil nutrients are likely to have positive environmental effects through reduced usage of chemicals in agriculture. This review assesses the available literature on differential uptake and utilization efficiency of K in farming systems. Large areas of agricultural land in the world are deficient in K (e.g. 3/4 of paddy soils in China, 2/3 of the wheatbelt in Southern Australia), with export in agricultural produce (especially hay) and leaching (especially in sandy soils) contributing to lowering of K content in the soil. The capacity of a genotype to grow and yield well in soils low in available K is K efficiency. Genotypic differences in efficiency of K uptake and utilization have been reported for all major economically important plants. The K-efficient phenotype is a complex one comprising a mixture of uptake and utilization efficiency mechanisms. Differential exudation of organic compounds to facilitate release of non-exchangeable K is one of the mechanisms of differential K uptake efficiency. Genotypes efficient in K uptake may have a larger surface area of contact between roots and soil and increased uptake at the root,soil interface to maintain a larger diffusive gradient towards roots. Better translocation of K into different organs, greater capacity to maintain cytosolic K+ concentration within optimal ranges and increased capacity to substitute Na+ for K+ are the main mechanisms underlying K utilization efficiency. Further breeding for increased K efficiency will be dependent on identification of suitable markers and compounding of efficiency mechanisms into locally adapted germplasm. [source] | |||||||||||||