376 research outputs found

    Predicting seed germination of winterfat (Eurotia lanata), a native forage species

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    Non-Peer ReviewedThe timing of seed germination plays a critical role in the survival of plants in natural ecosystems. Population-based models for the prediction of seed germination as the function of temperature and water potential have been developed, which can also be used in predicting field emergence. We used winterfat (Eurotia lanata) to test variations in parameters of the thermal time and hydrothermal time model among seed mass classes and germination conditions. Germination rates (GR) of subpopulations were estimated from germination time courses over a water potential range from 0 to –1.33 MPa at 2, 5, 10, 15, 20, and 25 oC. Estimated base temperature (Tb) was lower in the large seed mass class (-4.5 oC) than the small seed mass class (-3.5 oC). The ζ b(50) was lowest at intermediate temperatures between 10 to 15 oC. A linear increase of hydro time (ρH) with subpopulation was found at lower temperatures, especially at 2 oC. There were no significant differences in ζ b(50) between large and small seeds, but significant differences were observed in hydrothermal time requirement (ρHT(50)), which was lower at intermediate temperatures than at either lower or higher temperatures. The predictability of the thermal and hydrothermal time model was improved when parameters were allowed to change with seed size and germination conditions. Variations in Tb among seed mass classes favor large seeds, which accumulate more thermal time at a given temperature. This is particularly important for species such as winterfat, which germinates early in the season and early-emerged seedlings have better chance to establish and survive

    Leaf Cuticular Wax, a Trait for Multiple Stress Resistance in Crop Plants

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    Cuticular waxes form the primary interface between a plant and its external environment. The most important function of this hydrophobic interface is regulation of non-stomatal water loss, gas exchange and conferring resistance to a wide range of biotic as well as abiotic stresses. The biosynthesis, transport and deposition of the cuticular waxes are tightly coordinated by complex molecular networks, which are also often regulated in response to various developmental, biotic as well as abiotic cues. Evidences from model as well as non-model systems suggest that targeted manipulation of the molecular regulators of wax biosynthetic pathways could enhance plant resistance to multiple stresses as well as enhance the post-harvest quality of produce. Under the current scenario of varying climatic conditions, where plants often encounter multiple stress conditions, cuticular waxes is an appropriate trait to be considered for crop improvement programs, as any attempt to improve cuticular traits would be advantageous to the crop to enhance its adaptability to diverse adverse conditions. This chapter briefs on the significance of cuticular waxes in plants, its biosynthesis, transport and deposition, its implication on plant resistance to adverse conditions, and the current options in targeted manipulation of wax-traits for breeding new crop types

    Exchange flow between open water and floating vegetation

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    This study describes the exchange flow between a region with open water and a region with a partial-depth porous obstruction, which represents the thermally-driven exchange that occurs between open water and floating vegetation. The partial-depth porous obstruction represents the root layer, which does not penetrate to the bed. Initially, a vertical wall separates the two regions, with fluid of higher density in the obstructed region and fluid of lower density in the open region. This density difference represents the influence of differential solar heating due to shading by the vegetation. For a range of root density and root depths, the velocity distribution is measured in the lab using PIV. When the vertical wall is removed, the less dense water flows into the obstructed region at the surface. This surface flow bifurcates into two layers, one flowing directly through the root layer and one flowing beneath the root layer. A flow directed out of the vegetated region occurs at the bed. A model is developed that predicts the flow rates within each layer based on energy considerations. The experiments and model together suggest that at time- and length-scales relevant to the field, the flow structure for any root layer porosity approaches that of a fully blocked layer, for which the exchange flow occurs only beneath the root layer.National Science Foundation (U.S.) (grant EAR0509658

    Enhanced permeability due to apparent oil/brine slippage in limestone and its dependence on wettability

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    Acknowledgments This material includes work supported by a Society of Petrophysicists and Well Log Analysts Foundation grant and an Aberdeen Formation Evaluation Society scholarship. M.C. was supported by a University of Aberdeen College of Physical Sciences studentship. The authors gratefully acknowledge Amer Syed for his assistance with the assembly and maintenance of the coreflood rigs, Jim Anderson for helpful discussions, and the two anonymous reviewers for their comments and suggestions. All data used in this study will be made available from the corresponding author upon request.Peer reviewedPublisher PD

    A review of plant-flow interactions on salt marshes: the importance of vegetation structure and plant mechanical characteristics

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    Observations of plant-flow interactions on salt marshes have revealed a highly complex process dominated by the tightly coupled effects of plant characteristics and hydrodynamic conditions. This paper highlights the importance of vegetation structures such as plant density and height, as well as their spatial variability and mechanical properties including flexibility, upon energy dissipation and flow modification. Many field, laboratory and modelling studies which attempt to predict flow dissipation or improve our understanding of plant-flow interactions use simplified structural measures of salt marsh vegetation or artificial representations. These simplifications neglect important plant and canopy elements and are unlikely to be truly representative of their natural counterparts. Such approaches limit our understanding of plant-flow interactions and potentially compromise the predictive accuracy and application of numerical flow models. It is important therefore that improved techniques to measure vegetation structure are adopted in order to better define the key relationships between measurable plant characteristics and drag-relevant plant properties.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/wat2.110

    Theory of the beta-type Organic Superconductivity under Uniaxial Compression

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    We study theoretically the shift of the superconducting transition temperature (Tc) under uniaxial compression in beta-type organic superconductors, beta-(BEDT-TTF)2I3 and beta-(BDA-TTP)2X[X=SbF6,AsF6], in order to clarify the electron correlation, the spin frustration and the effect of dimerization. The transfer integrals are calculated by the extended Huckel method assuming the uniaxial strain and the superconducting state mediated by the spin fluctuation is solved using Eliashberg's equation with the fluctuation-exchange approximation. The calculation is carried out on both the dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found that (i) the behavior of Tc in beta-(BEDT-TTF)2I3 with a stronger dimerization is well reproduced by the dimer model, while that in weakly dimerized beta-BDA-TTP salts is rather well reproduced by the two-band model, and (ii) the competition between the spin frustration and the effect induced by the fluctuation is important in these materials, which causes nonmonotonic shift of Tc against uniaxial compression.Comment: 18 pages, 16 figures, 2 tabl

    Evidence for Modification of the Electronic Density-of-States by Zero-Point Lattice Motion in One-Dimension - Luminescence and Resonance Raman Studies of An Mx Solid

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    Luminescence spectra, both emission and excitation, and the excitation dependence of the resonance Raman spectra, have been measured for the quasi-one-dimensional charge-density-wave material [Pt(en)2][Pt(en)2Cl2](ClO4)4, en = 1,2-diaminoethane. While the luminescence experiments show the existence of tail states at low temperature in the band gap region, the Raman measurements conclusively demonstrate that this tail does not arise from ordinary static structural disorder. These results can be explained by considering the zero-point motion of the lattice

    A stem spacing‐based non‐dimensional model for predicting longitudinal dispersion in low‐density emergent vegetation

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    Predicting how pollutants disperse in vegetation is necessary to protect natural watercourses. This can be done using the one-dimensional advection dispersion equation, which requires estimates of longitudinal dispersion coefficients in vegetation. Dye tracing was used to obtain longitudinal dispersion coefficients in emergent artificial vegetation of different densities and stem diameters. Based on these results, a simple non-dimensional model, depending on velocity and stem spacing, was developed to predict the longitudinal dispersion coefficient in uniform emergent vegetation at low densities (solid volume fractions < 0.1). Predictions of the longitudinal dispersion coefficient from this simple model were compared with predictions from a more complex expression for a range of experimental data, including real vegetation. The simple model was found to predict correct order of magnitude dispersion coefficients and to perform as well as the more complex expression. The simple model requires fewer parameters and provides a robust engineering approximation

    Gravity Currents in Aquatic Canopies

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    A lock exchange experiment is used to investigate the propagation of gravity currents through a random array of rigid, emergent cylinders which represents a canopy of aquatic plants. As canopy drag increases, the propagating front varies from the classic profile of an unobstructed gravity current to a triangular profile. Unlike the unobstructed lock exchange, the gravity current in the canopy decelerates with time as the front lengthens. Two drag-dominated regimes associated with linear and nonlinear drag laws are identified. The theoretical expression for toe velocity is supported by observed values. Empirical criteria are developed to predict the current regime from the cylinder Reynolds number and the array density.National Science Foundation (U.S.) (grant EAR0309188)National Science Foundation (U.S.) (grant EAR0509658)Massachusetts Institute of Technology (Presidential Graduate Fellowship