Investigating soil moisture-climate interactions in a changing climate: A review

Abiotic stresses, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress are serious threats to agriculture and the natural status of the environment. Increased salinization of arable land is expected to have devastating global effects, resulting in 30% land loss within the next 25 years, and up to 50% by the year 2050. Therefore, breeding for drought and salinity stress tolerance in crop plants (for food supply) and in forest trees (a central component of the global ecosystem) should be given high research priority in plant biotechnology programs. Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses, such as signaling, transcriptional control, protection of membranes and proteins, and free-radical and toxic-compound scavenging. Recently, research into the molecular mechanisms of stress responses has started to bear fruit and, in parallel, genetic modification of stress tolerance has also shown promising results that may ultimately apply to agriculturally and ecologically important plants. The present review summarizes the recent advances in elucidating stress-response mechanisms and their biotechnological applications. Emphasis is placed on transgenic plants that have been engineered based on different stress-response mechanisms. The review examines the following aspects: regulatory controls, metabolite engineering, ion transport, antioxidants and detoxification, late embryogenesis abundant (LEA) and heat-shock proteins.

/pdf/plant-responses-to-drought-salinity-and-extreme-temperatures-2t6tpv484r.pdf

Plant responses to drought, salinity and extreme temperatures: towards genetic engineering for stress tolerance

Cold, salinity and drought stresses: an overview.

There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role alon...

Mechanisms of Slow Sorption of Organic Chemicals to Natural Particles

Substantial advances in the measurement of water content and bulk soil electrical conductivity (EC) using time domain reflectometry (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material and the fact that there is a good relationship between the permittivity of a material and its water content. A further advantage is the ability to estimate water content and measure bulk soil EC simultaneously using TDR. The aim of this review is to summarize and examine advances that have been made in terms of measuring permittivity and bulk EC. The review examines issues such as the effective frequency of the TDR measurement and waveform analysis in dispersive dielectrics. The growing importance of both waveform simulation and inverse analysis of waveforms is highlighted. Such methods hold great potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guidance is given for probe construction. The importance of TDR measurement sampling volume is considered and the relative energy storage density is modeled for a range of probe designs. Tables are provided that compare some of the different aspects of commercial TDR equipment, and the units are discussed in terms of their performance and their advantages and disadvantages. It is hoped that the review will provide an informative guide to the more technical aspects of permittivity and EC measurement using TDR for the novice and expert alike.

A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Physical constraints affecting bacterial habitats and activity in unsaturated porous media – a review

http://directory.umm.ac.id/Data%20Elmu/jurnal/P/PlantScience/PlantScience_Elsevier/Vol155.Issue1.2000/5295.pdf

Improved biomass productivity and water use efficiency under water deficit conditions in transgenic wheat constitutively expressing the barley HVA1 gene

Time domain reflectometry (TDR) is a highly accurate and automatable method for determination of porous media water content and electrical conductivity. Water content is inferred from the dielectric permittivity of the medium, whereas electrical conductivity is inferred from TDR signal attenuation. Empirical and dielectric mixing models are used to relate water content to measured dielectric permittivity. Clay and organic matter bind substantial amounts of water, such that measured bulk dielectric constant is reduced and the relationship with total water content requires individual calibration. A variety of TDR probe configurations provide users with site- and media-specific options. Advances in TDR technology and in other dielectric methods offer the promise not only for less expensive and more accurate tools for electrical determination of water and solute contents, but also a host of other properties such as specific surface area, and retention properties of porous media. Copyright © 2002 John Wiley & Sons, Ltd.

Time domain reflectometry measurement principles and applications

Near-surface measurements of soil water content (θ) using time domain reflectometry (TDR) may exhibit anomalous behavior in the presence of diurnal temperature (T) fluctuations. Experimental results obtained in a companion paper led to the hypothesis that the observed bulk dielectric permittivity (ϵb) is determined by an interplay between two competing phenomena: (1) the reduction in the dielectric permittivity of bulk water with increased T; and (2) the increase in TDR-measured ϵb with increased T due to release of bound water. In this study we develop a physically based model for the temperature dependency of TDR-measured soil bulk dielectric permittivity and propose practical correction factors. The model considers the modified properties of water near solid surfaces to define a layer of rotationally hindered water (within the TDR frequency bandwidth) having a temperature dependent thickness. Changes in measured ϵb(T) are thus attributed to variations in the thickness of the rotationally hindered layer which has a lower dielectric permittivity than free water and hence is less “visible” to travel-time-based TDR waveform analyses. The model is sensitive to the soil specific surface area and the water content, both of which determine the ratio of bound to bulk soil water. Comparisons with experimental data covering a wide range of soils, water contents, and temperatures showed good agreement. Further studies are needed to evaluate some of the model's critical parameters such as the cutoff frequency below which water is considered bound. A temperature correction approximation is based on analytical expressions for TDR-measured bulk dielectric permitivity and requires estimates of soil specific surface area and bulk density, which may be estimated from soil texture. The thermodielectric sensitivity of TDR-measured bulk dielectric permittivity and water content may serve as a basis for estimating soil specific surface area.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998WR900008

Jon M. Wraith

Papers

A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Physical constraints affecting bacterial habitats and activity in unsaturated porous media – a review

Improved biomass productivity and water use efficiency under water deficit conditions in transgenic wheat constitutively expressing the barley HVA1 gene

Time domain reflectometry measurement principles and applications

Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: A physical model