Since many processes in soil are highly sensitive to soil structure, this review intends to evaluate the potential of observable soil structural attributes to be used in the assessment of soil ...functions. We focus on the biomass production, storage and filtering of water, storage and recycling of nutrients, carbon storage, habitat for biological activity, and physical stability and support. A selection of frequently used soil structural properties are analyzed and discussed from a methodological point of view and with respect to their relevance to soil functions. These are properties extracted from soil profile description, visual soil assessment, aggregate size and stability analysis, bulk density, mercury porosimetry, water retention curve, gas adsorption, and imaging techniques. We highlight the greater relevance of the pore network characterization as compared to the aggregate perspective. We identify porosity, macroporosity, pore distances, and pore connectivity derived from imaging techniques as being the most relevant indicators for several soil functions. Since imaging techniques are not widely accessible, we suggest using this technique to build up an open access “soil structure library” for a large range of soil types, which could form the basis to relate more easily available measures to pore structural attributes in a site-specific way (i.e., taking into account texture, soil organic matter content, etc.).
•Structural properties are discussed with respect to their relevance to soil functions.•Pore network characterization is more powerful than analyzing disturbed aggregates.•We identified porosity, macroporosity, pore distances, and pore connectivity.•Imaging instruments appeared to be the most reliable tools to measure them.•We suggest developing an open access “soil structure library”.
The macroscopic description of the hysteretic behavior of two‐phase flow in porous media remains a challenge. It is not obvious how to represent the underlying pore‐scale processes at the Darcy‐scale ...in a consistent way. Darcy‐scale thermodynamic models do not completely eliminate hysteresis and our findings indicate that the shape of displacement fronts is an additional source of hysteresis that has not been considered before. This is a shortcoming because effective process behavior such as trapping efficiency of CO2 or oil production during water flooding are directly linked to pore‐scale displacement mechanisms with very different front shape such as capillary fingering, flat frontal displacement, or cluster growth. Here we introduce fluid topology, expressed by the Euler characteristic of the nonwetting phase (χn), as a shape measure of displacement fronts. Using two high‐quality data sets obtained by fast X‐ray tomography, we show that χn is hysteretic between drainage and imbibition and characteristic for the underlying displacement pattern. In a more physical sense, the Euler characteristic can be interpreted as a parameter describing local fluid connectedness. It may provide the closing link between a topological characterization and macroscopic formulations of two‐phase immiscible displacement in porous rock. Since fast X‐ray tomography is currently becoming a mature technique, we expect a significant growth in high‐quality data sets of real time fluid displacement processes in the future. The novel measures of fluid topology presented here have the potential to become standard metrics needed to fully explore them.
Key Points:
Real‐time fluid displacement analysis with fast synchrotron‐based X‐ray tomography
Changes in fluid topology are characteristic for the underlying displacement mechanisms
Fluid topology correlates well with fluid trapping
Misuse and overuse of antibiotics have contributed in the last decades to a phenomenon known as antibiotic resistance which is currently considered one of the principal threats to global public ...health by the World Health Organization. The aim to find alternative drugs has been demonstrated as a real challenge. Thanks to their biodiversity, insects represent the largest class of organisms in the animal kingdom. The humoral immune response includes the production of antimicrobial peptides (AMPs) that are released into the insect hemolymph after microbial infection. In this review, we have focused on insect immune responses, particularly on AMP characteristics, their mechanism of action and applications, especially in the biomedical field. Furthermore, we discuss the Toll, Imd, and JAK-STAT pathways that activate genes encoding for the expression of AMPs. Moreover, we focused on strategies to improve insect peptides stability against proteolytic susceptibility such as D-amino acid substitutions, N-terminus modification, cyclization and dimerization.
The structure of soils and other geologic media is a complex three-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately ...linked to the structure given by the pore space and its spatial distribution. It is an old dream and still a formidable challenge to relate structural features of porous media to their functional properties. Using tomographic techniques, soil structure can be directly observed at a range of spatial scales. In this paper we present a scale-invariant concept to quantify complex structures based on a limited set of meaningful morphological functions. They are based on
d+1 Minkowski functionals as defined for
d-dimensional bodies. These basic quantities are determined as a function of pore size or aggregate size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on the size of pores and aggregates, the pore surface area and the pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the pore structure of an arable soil and the pore structure of a sand both obtained by X-ray micro-tomography. We also analyze the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale using samples of different size recorded at different resolutions. The results demonstrate that objects smaller than 5 voxels are critical for quantitative analysis.
Do roots mind the gap? Carminati, A.; Vetterlein, D.; Koebernick, N. ...
Plant and soil,
06/2013, Letnik:
367, Številka:
1/2
Journal Article
Recenzirano
Odprti dostop
Aims Roots need to be in good contact with the soil to take up water and nutrients. However, when the soil dries and roots shrink, air-filled gaps form at the rootsoil interface. Do gaps actually ...limit the root water uptake, or do they form after water flow in soil is already limiting? Methods Four white lupins were grown in cylinders of 20 cm height and 8 cm diameter. The dynamics of root and soil structure were recorded using X-ray CT at regular intervals during one drying/wetting cycle. Tensiometers were inserted at 5 and 18 cm depth to measure soil matric potential. Transpiration rate was monitored by continuously weighing the columns and gas exchange measurements. Results Transpiration started to decrease at soil matric potential ø between -5 kPa and -10 kPa. Air-filled gaps appeared along tap roots between Ψ=-10 kPa and Ψ=-20 kPa. As Ψ decreased below -40 kPa, roots further shrank and gaps expanded to 0.1 to 0.35 mm. Gaps around lateral roots were smaller, but a higher resolution is required to estimate their size. Conclusions Gaps formed after the transpiration rate decreased. We conclude that gaps are not the cause but a consequence of reduced water availability for lupins.
The calculation of the relative hydraulic conductivity function based on water retention data is an attractive and widely used approach, since direct measurements of unsaturated conductivities are ...difficult. We show theoretically under which conditions an air-entry value for water retention data is definitely required when using the statistical approach of Mualem. Moreover we rigorously specify the conditions for which the classical van Genuchten–Mualem model leads to wrong predictions of relative hydraulic conductivity and, hence, an alternative formulation including an air-entry value should be used. Significant consequences are demonstrated for the inverse parameter estimation based on multistep outflow experiments. Furthermore it is shown that the use of a physically correct formulation of the water retention curve including an air-entry value and the derived hydraulic conductivity function influences not only the stability of numerical simulations but also their final results. This is especially grave as simulations with van Genuchten–Mualem parameters are frequently used to compare experiments and simulations and to draw conclusions on the correctness of Richards’ equation.
Altered nonverbal communication patterns especially with regard to gaze interactions are commonly reported for persons with autism spectrum disorder (ASD). In this study we investigate and ...differentiate for the first time the interplay of attention allocation, the establishment of shared focus (eye contact and joint attention) and the recognition of intentions in gaze interactions in adults with ASD compared to control persons. Participants interacted via gaze with a virtual character (VC), who they believed was controlled by another person. Participants were instructed to ascertain whether their partner was trying to interact with them. In fact, the VC was fully algorithm-controlled and showed either interactive or non-interactive gaze behavior. Participants with ASD were specifically impaired in ascertaining whether their partner was trying to interact with them or not as compared to participants without ASD whereas neither the allocation of attention nor the ability to establish a shared focus were affected. Thus, perception and production of gaze cues seem preserved while the evaluation of gaze cues appeared to be impaired. An additional exploratory analysis suggests that especially the interpretation of contingencies between the interactants' actions are altered in ASD and should be investigated more closely.
The aim of TERENO (TERrestrial ENvironmental Observatories) is to collect long-term observation data on the hydrosphere, biosphere, pedosphere, lower atmosphere and anthroposphere along multiple ...spatial and temporal gradients in climate sensitive regions across Germany. The lysimeter-network SOILCan was installed as a part of TERENO between March and December 2010 within the four observatories. It represents a long-term large-scale experiment to study the effects of climate and management changes in terrestrial ecosystems, with particular focus on the impact of these changes on water, energy and matter fluxes into groundwater and atmosphere. SOILCan primarily focuses on soil hydrology, the carbon and nutrient cycle and plant species diversity. Time series measurements of states and fluxes at high spatial and temporal resolution in the soil and biosphere are combined with remote sensing information for the development and calibration of process-based models simulating impacts of climate change in soil processes at field to regional scale. Within the framework of SOILCan, 132 fully automated lysimeter systems were installed at 14 highly equipped experimental field sites across the four TERENO observatories. Relevant state variables of grassland and arable ecosystems are monitored characterizing climate, hydrology and matter fluxes into the atmosphere and within the hydrosphere as well as plant species diversity. Lysimeters are either being operated at or near their original sampling location or were transferred within or between the four TERENO observatories thereby using temperature and rainfall gradients to mimic future climatic conditions (space for time), which allow measuring impacts of climate change on terrestrial ecosystems. The lysimeters are cultivated as grassland (intensive, extensive and non-used) or arable land, the latter with a standardized crop rotation of winter wheat—winter barley—winter rye—oat. This publication describes the general design of the SOILCan experiment including a comprehensive description of the pedological characteristics of the different sites and presents a few exemplary results from the first years of operation.
Centrifugation provides a fast method to measure soil water retention curves over a wide moisture range. However, deformation of soil structure may occur at high angular velocities in the centrifuge. ...The objective of this study was to capture these changes in soil structure with X-ray microtomography and to measure local deformations via digital volume correlation. Two samples were investigated that differ in texture and rock content. A detailed analysis of the pore space reveals an interplay between shrinkage due to drying and soil compaction due to compression. Macroporosity increases at moderate angular velocity because of crack formation due to moisture release. At higher angular velocities, corresponding to capillary pressure of psi<-100kPa, macroporosity decreases again because of structure deformation due to compression. While volume changes due to swelling clay minerals are immanent in any drying process, the compaction of soil is a specific drawback of the centrifugation method. A new protocol for digital volume correlation was developed to analyze the spatial heterogeneity of deformation. In both samples the displacement of soil constituents is highest in the top part of the sample and exhibits high lateral variability explained by the spatial distribution of macropores in the sample. Centrifugation should therefore only be applied after the completion of all other hydraulic or thermal experiments, or any other analysis that depends on the integrity of soil structure.
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