Biogeochemical interfaces shape microbial community function in soil. On the other hand microbial communities influence the properties of biogeochemical interfaces. Despite the importance of this interplay, basic understanding of the role of biogeochemical interfaces for microbial performance is still missing. We postulate that biogeochemical interfaces in soil are important for the formation of functional consortia of microorganisms, which are able to shape their own microenvironment and therefore influence the properties of interfaces in soil. Furthermore biogeochemical interfaces act as genetic memory of soils, as they can store DNA from dead microbes and protect it from degradation. We propose that for the formation of functional biogeochemical interfaces microbial dispersal (e.g. along fungal networks) in response to quality and quantity of bioavailable carbon and/or water availability plays a major role, as the development of functional guilds of microbes requires energy and depends on the redox state of the habitat.To address these questions, hexadecane degradation will be studied in differently developed artificial and natural soils. To answer the question on the role of carbon quantity and quality, experiments will be performed with and without litter material at different water contents of the soil. Experiments will be performed with intact soil columns as well as soil samples where the developed interface structure has been artificially destroyed. Molecular analysis of hexadecane degrading microbial communties will be done in vitro as well as in situ. The corresponding toolbox has been successfully developed in the first phase of the priority program including methods for genome, transcriptome and proteome analysis.
In structured soils, the interaction of percolating water and reactive solutes with the soil matrix is mostly restricted to the surfaces of preferential flow paths. Flow paths, i.e., macropores, are formed by worm burrows, decayed root channels, cracks, and inter-aggregate spaces. While biopores are covered by earthworm casts and mucilage or by root residues, aggregates and cracks are often coated by soil organic matter (SOM), oxides, and clay minerals especially in the clay illuviation horizons of Luvisols. The SOM as well as the clay mineral composition and concentration strongly determine the wettability and sorption capacity of the coatings and thus control water and solute movement as well as the mass exchange between the preferential flow paths and the soil matrix. The objective of this proposal is the quantitative description of the small-scale distribution of physicochemical properties of intact structural surfaces and flow path surfaces and of their distribution in the soil volume. Samples of Bt horizons of Luvisols from Loess will be compared with those from glacial till. At intact structural surfaces prepared from soil clods, the spatial distribution (mm-scale) of SOM and clay mineral composition will be characterized with DRIFT (Diffuse reflectance infrared Fourier transform) spectroscopy using a self-developed mapping technique. For samples manually separated from coated surfaces and biopore walls, the contents of organic carbon (Corg) and the cation exchange capacity (CEC) will be analyzed and related to the intensities of specific signals in DRIFT spectra using Partial Least Square Regression (PLSR) analysis. The signal intensities of the DRIFT mapping spectra will be used to quantify the spatial distribution of Corg and CEC at these structural surfaces. The DRIFT mapping data will also be used for qualitatively characterizing the small scale distribution of the recalcitrance, humification, and microbial activity of the SOM from structural surfaces. The clay mineral composition of defined surface regions will be characterized by combining DRIFT spectroscopic with X-ray diffractometric analysis of manually separated samples. Subsequently, the spatial distribution of the clay mineral composition at structural surfaces will be determined from the intensities of clay mineral-specific signals in the DRIFT mapping spectra and exemplarily compared to scanning electron microscopic and infrared microscopic analysis of thin sections and thin polished micro-sections. The three-dimensional spatial distribution of the total structural surfaces in the volume of the Bt horizons will be quantified using X-ray computed tomography (CT) analysis of soil cores. The active preferential flow paths will be visualized and quantified by field tracer experiments. These CT and tracer data will be used to transfer the properties of the structural surfaces characterized by DRIFT mapping onto the active preferential flow paths in the Bt horizons.
The overarching goal of our proposal is to understand the regulation of organic carbon (OC) transfor-mation across terrestrial-aquatic interfaces from soil, to lotic and lentic waters, with emphasis on ephemeral streams. These systems considerably expand the terrestrial-aquatic interface and are thus potential sites for intensive OC-transformation. Despite the different environmental conditions of ter-restrial, semi-aquatic and aquatic sites, likely major factors for the transformation of OC at all sites are the quality of the organic matter, the supply with oxygen and nutrients and the water regime. We will target the effects of (1) OC quality and priming, (2) stream sediment properties that control the advective supply of hyporheic sediments with oxygen and nutrients, and (3) the water regime. The responses of sediment associated metabolic activities, C turn-over, C-flow in the microbial food web, and the combined transformations of terrestrial and aquatic OC will be quantified and characterized in complementary laboratory and field experiments. Analogous mesocosm experiments in terrestrial soil, ephemeral and perennial streams and pond shore will be conducted in the experimental Chicken Creek catchment. This research site is ideal due to a wide but well-defined terrestrial-aquatic transition zone and due to low background concentrations of labile organic carbon. The studies will benefit from new methodologies and techniques, including development of hyporheic flow path tubes and comparative assessment of soil and stream sediment respiration with methods from soil and aquatic sciences. We will combine tracer techniques to assess advective supply of sediments, respiration measurements, greenhouse gas flux measurements, isotope labeling, and isotope natural abundance studies. Our studies will contribute to the understanding of OC mineralization and thus CO2 emissions across terrestrial and aquatic systems. A deeper knowledge of OC-transformation in the terrestrial-aquatic interface is of high relevance for the modelling of carbon flow through landscapes and for the understanding of the global C cycle.
Teilprojekt C05 hat zum Ziel, den wichtigen Eintragsweg für Kunststoffe, in Form von Mikroplastik, in die Umwelt aus technischen Anlagen (MP) mechanistisch aufzuklären. Gleichzeitig sollen neue Ansätze verfolgt werden, die zur Vermeidung bzw. Reduktion von MP aus Standardkunststoffen maßgeblich beitragen sollen. Zu diesem Zweck sollen Polyethylen, Polypropylen, Polystyrol, Nylon, Polyethylenterephthalat, Polyisopren und Polyvinylchlorid durch Beschleuniger (in situ) in ihren Oberflächeneigenschaften für die Biofilmbildung modifiziert und dadurch unter Prozessbedingungen biologisch angreifbar und abbaubar gemacht werden. So können auch Standardkunststoffe umweltverträglicher bezüglich der MP-Partikel Bildung werden. Damit geht TP C05 weit über die bislang üblichen eher deskriptiven Studien zu MP in technischen Anlagen und der Umwelt hinaus. Folgende zentrale Fragen sollen in TP C05 in Hinblick MP-Partikel in technischen Anlagen der Abfall- und Abwasserwirtschaft beantwortet werden: 1. Kommt es in den Anlagen zu spezifischen (biologischen) Abbau- und Degradationsvorgängen? 2. Wie hängen die zu beobachtenden Prozesse von MP-Charakteristika (Materialsorte, Zusammensetzung, Größe, Morphologie, Beschichtung) ab, ? 3. Lassen sich die Vorgänge ('Bioabbaubarkeit') durch gezielte Modifikation der Partikeloberfläche vor oder in den Anlagen beschleunigen? 4. Welche ökologischen Konsequenzen einer Ausbringung der (modifizierten) Partikel in die Umwelt und hier vor allem in den Boden lassen sich postulieren?
We are currently facing the urgent need to improve our understanding of carbon cycling in subsoils, because the organic carbon pool below 30 cm depth is considerably larger than that in the topsoil and a substantial part of the subsoil C pool appears to be much less recalcitrant than expected over the last decades. Therefore, small changes in environmental conditions could change not only carbon cycling in topsoils, but also in subsoils. While organic matter stabilization mechanisms and factors controlling its turnover are well understood in topsoils, the underlying mechanisms are not valid in subsoils due to depth dependent differences regarding (1) amounts and composition of C-pools and C-inputs, (2) aeration, moisture and temperature regimes, (3) relevance of specific soil organic carbon (SOC) stabilisation mechanisms and (4) spatial heterogeneity of physico-chemical and biological parameters. Due to very low C concentrations and high spatio-temporal variability of properties and processes, the investigation of subsoil phenomena and processes poses major methodological, instrumental and analytical challenges. This project will face these challenges with a transdisciplinary team of soil scientists applying innovative approaches and considering the magnitude, chemical and isotopic composition and 14C-content of all relevant C-flux components and C-fractions. Taking also the spatial and temporal variability into account, will allow us to understand the four-dimensional changes of C-cycling in this environment. The nine closely interlinked subprojects coordinated by the central project will combine field C-flux measurements with detailed analyses of subsoil properties and in-situ experiments at a central field site on a sandy soil near Hannover. The field measurements are supplemented by laboratory studies for the determination of factors controlling C stabilization and C turnover. Ultimately, the results generated by the subprojects and the data synthesized in the coordinating project will greatly enhance our knowledge and conceptual understanding of the processes and controlling factors of subsoil carbon turnover as a prerequisite for numerical modelling of C-dynamics in subsoils.
Lärm und unkontrollierte Vibrationen sind in vielen industriellen und geotechnischen Anwendungen problematisch. Akustische Wellen auf Straßen und Schiene, oder verursacht durch Erdbeben, pflanzen sich durch die typischerweise granularen Strukturen im Boden, in Beton, oder in Asphalt mit einer ganz eigenen Charakteristik fort, wobei das Material die Geschwindigkeit, die Dämpfung und den Frequenzbereich der transmittierten Wellen beeinflusst. In unserem innovativen Projekt wollen wir granulare Materialien in 'granulare Dämpfer' verwandeln indem wir sowohl Teilcheneigenschaften als auch die Mischungszusammensetzung der weichen bzw. steifen Teilchen einer granularen Mischung in weiten Bereichen variieren. Das Ziel ist, effektive Materialeigenschaften wie Dämpfung oder Dispersion zu optimieren, und Frequenzfilterung durch Bandlücken optimal auszunutzen. Um dieses Ziel zu erreichen werden wir das Projekt von zwei Seiten aufrollen: Einerseits werden wir physikalische Experimente durchführen in denen wir Materialien mit unterschiedlichsten dämpfenden und elastischen Eigenschaften in allen Mischverhältnissen kombinieren. Andererseits werden wir dazu komplementär auch direkte Teilchen-Simulationen (DEM) durchführen um die mikromechanischen Mechanismen abzubilden und die effektiven Eigenschaften der Mischung quantitativ zu modellieren und zu verstehen. Nach sorgfältigster Analyse werden sowohl die experimentellen als auch die numerischen Daten dazu verwendet um ein stochastisches makroskopisches Modell weiterzuentwickeln das den Transport von Energie zwischen verschiedenen Frequenzbändern mit einer Master-Gleichung beschreibt. Dies kann schlussendlich dazu verwendet werden um in vielen Anwendungen neue, bessere Materialeigenschaften zu erzielen. Vorarbeiten: In den letzten Jahren habe wir bereits Wellenausbreitung und Dämpfung in granularen Mischungen von weichen und harten Teilchen unter verschiedenen hydrostatischen Kompressionsdrücken untersucht. Bisher konzentrierten wir uns auf mono-disperse Glas-Gummi Mischungen um das Zusammenspiel von Komposition und Spannungszustand zu verstehen. Ein überraschendes Ergebnis ist dabei, dass wir leichtere Packungen mit 15-20% Gummi herstellen konnten die bessere elastische und viel bessere Dämpfungseigenschaften hatten. Arbeitsplan: Zuerst wollen wir den kombinierten Einfluss von verschieden großen weichen und harten Teilchen in Mischungen untersuchen. Nach sorgfältiger Analyse im Frequenz-Raum werden wir die komplexe Wechselwirkung zwischen Teilchen- und System-Eigenschaften, sowie zwischen Energie-Absorption und -Propagation benutzen um ein stochastisches Model reduzierter Ordnung zu formulieren, das die Fortpflanzung von Wellen für alle Frequenzen in Raum und Zeit vorhersagen kann. Innovativ ist, dass wir nicht nur die niedrigeren Eigenfrequenzen modellieren, sondern alle Frequenzen, da insbesondere die hohen Frequenzen am wichtigsten für die Dämpfungseigenschaften in der Anwendung sind.
It is well established that reduced supply of fresh organic matter, interactions of organic matter with mineral phases and spatial inaccessibility affect C stocks in subsoils. However, quantitative information required for a better understanding of the contribution of each of the different processes to C sequestration in subsoils and for improvements of subsoil C models is scarce. The same is true for the main controlling factors of the decomposition rates of soil organic matter in subsoils. Moreover, information on spatial variabilities of different properties in the subsoil is rare. The few studies available which couple near and middle infrared spectroscopy (NIRS/MIRS) with geostatistical approaches indicate a potential for the creation of spatial maps which may show hot spots with increased biological activities in the soil profile and their effects on the distribution of C contents. Objectives are (i) to determine the mean residence time of subsoil C in different fractions by applying fractionation procedures in combination with 14C measurements; (ii) to study the effects of water content, input of 13C-labelled roots and dissolved organic matter and spatial inaccessibility on C turnover in an automatic microcosm system; (iii) to determine general soil properties and soil biological and chemical characteristics using NIRS and MIRS, and (iv) to extrapolate the measured and estimated soil properties to the vertical profiles by using different spatial interpolation techniques. For the NIRS/MIRS applications, sample pretreatment (air-dried vs. freeze-dried samples) and calibration procedures (a modified partial least square (MPLS) approach vs. a genetic algorithm coupled with MPLS or PLS) will be optimized. We hypothesize that the combined application of chemical fractionation in combination with 14C measurements and the results of the incubation experiments will give the pool sizes of passive, intermediate, labile and very labile C and N and the mean residence times of labile and very labile C and N. These results will make it possible to initialize the new quantitative model to be developed by subproject PC. Additionally, we hypothesize that the sample pretreatment 'freeze-drying' will be more useful for the estimation of soil biological characteristics than air-drying. The GA-MPLS and GA-PLS approaches are expected to give better estimates of the soil characteristics than the MPLS and PLS approaches. The spatial maps for the different subsoil characteristics in combination with the spatial maps of temperature and water contents will presumably enable us to explain the spatial heterogeneity of C contents.
Atmospheric CO2 concentrations present a repetitive pattern of gradual decline and rapid increase during the last climate cycles, closely related to temperature and sea level change. During the Last Glacial Maximum (LGM; 23-19 kyr BP), when sea level was ca. 120 m below present, the ocean must have stored additionally about 750 Gt carbon. There is consensus that the Southern Ocean represents a key area governing past and present CO2 change. The latter is not only of high scientific but also of socio-economic and political concern since the Southern Ocean provides the potential for an efficient sink of anthropogenic carbon. However, the sensitivity of this carbon sink to climate-change induced reorganizations in wind patterns, ocean circulation, stratification, sea ice extent and biological production remains under debate. Models were not yet able to reproduce the necessary mechanisms involved, potentially due to a lack of the dynamic representation/resolution of atmospheric and oceanic circulation as well as missing carbon cycling. Data on past Southern Ocean hydrography and productivity are mainly from the Atlantic sector, thus do not adequately document conditions in the Pacific sector. This sector is not only the largest part of the Southern Ocean, but it also represents the main drainage area of the marine-based West Antarctic Ice Sheet (WAIS). In the proposed study we aim to generate paleo-data sets with a newly established proxy method from sediment core transects across the Pacific Southern Ocean. This will enhance the baselines for the understanding and modeling of the Southern Ocean's role in carbon cyling, i.e. ocean/atmosphere CO2 exchange and carbon sequestration. It will also allow insight into the response of the WAIS to past warmer than present conditions. Paired isotope measurements (oxygen, silicon) will be made on purified diatoms and radiolarians to describe glacial/interglacial contrasts in physical and nutrient properties at surface and subsurface water depth. This will be used to test (i) the impact of yet unconsidered dust-borne micronutrient deposition on the glacial South Pacific on shifts of primary productivity, Si-uptake rates and carbon export, (ii) the 'silicic-acid leakage' hypothesis (SALH) and (iii) the formation and extent of surface water stratification. Diatom and radiolarian oxygen isotopes will provide information on the timing of surface ocean salinity anomalies resulting from WAIS melt water. Climate model simulations using a complex coupled atmosphere ocean general circulation model (AOGCM) in combination with a sophisticated ocean biogeochemical model including Si-isotopes will be used for comparison with the paleo records. The analysis will cover spatial as well as temporal variability patterns of Southern Ocean hydrography, nutrient cycling and air-sea CO2-exchange. With the help of the climate model we aim to better separate and statistically analyse the individual impacts of ocean circulation and bio
Electrical conductivity is a key parameter in models of magnetic field generation in planetary interiors through magneto-hydrodynamic convection. Measurements of this key material parameter of liquid metals is not possible to date by experiments at relevant conditions, and dynamo models rely on extrapolations from low pressure/temperature experiments, or more recently on ab-initio calculations combining molecular dynamics and linear response calculations, using the Kubo-Greenwood formulation of transport coefficients. Such calculations have been performed for Fe, Fe-alloys, H, He and H-He mixtures to cover the interior of terrestrial and giant gas planets. These simulations are computationally expensive, and an efficient accurate scheme to determine electrical conductivities is desirable. Here we propose a model that can, at much lower computational costs, provide this information. It is based on Ziman theory of electrical conductivity that uses information on the liquid structure, combined with an internally consistent model of potentials for the electron-electron, electron-atom, and atom-atom interactions. In the proposal we formulate the theory and expand it to multi-component systems. We point out that fitting the liquid structure factor is the critical component in the process, and devise strategies on how this can be done efficiently. Fitting the structure factor in a thermodynamically consistent way and having a transferable electron-atom potential we can then relatively cheaply predict the electrical conductivity for a wide range of conditions. Only limited molecular dynamics simulations to obtain the structure factors are required.In the proposed project we will test and advance this model for liquid aluminum, a free-electron like metal, that we have studied with the Kubo-Greenwood method previously. We will then be able to predict the conductivities of Fe, Fe-light elements and H, He, as well as the H-He system that are relevant to the planetary interiors of terrestrial and giant gas planets, respectively.
Rain-cracking limits the production of many soft and fleshy fruit including sweet cherries world wide. Cracking is thought to result from increased water uptake through surface and pedicel. Water uptake increases fruit volume, and hence, turgor of cells (Pcell) and the pressure inside the fruit (Pfruit) and subjects the skin to tangential stress and hence, strain. When the strain exceeds the limits of extensibility the fruit cracks. This hypothesis is referred to as the Pfruit driven strain cracking. Based on this hypothesis cracking is related to two independent groups of factors: (1) water transport characteristics and (2) the intrinsic cracking susceptibility of the fruit defined as the amount of cracking per unit water uptake. The intrinsic cracking susceptibility thus reflects the mechanical constitution of the fruit. Most studies focussed on water transport through the fruit surface (factors 1), but only little information is available on the mechanical constitution (i.e., Pfruit and Pcell, tensile properties such as fracture strain, fracture pressure and modulus of elasticity of the exocarp; factors 2). The few published estimates of Pfruit in sweet cherry are all obtained indirectly (calculated from fruit water potential and osmotic potentials of juice extracts) and unrealistically high. They exceed those measured by pressure probe techniques in mature grape berry by several orders of magnitude. The objective of the proposed project is to test the hypothesis of the Pfruit driven strain cracking. Initially we will focus on establishing systems of widely differing intrinsic cracking susceptibility by varying species (sweet and sour cherry, Ribes and Vaccinium berries, plum, tomato), genotype (within sweet cherry), stage of development and temperature. These systems will then be used for testing the hypothesis of Pfruit driven strain cracking. We will quantify Pfruit und Pcell by pressure probe techniques and compression tests and the mechanical properties of the exocarp using biaxial tensile tests. When the presence of high Pfruit and Pcell is confirmed by direct measurements, subsequent studies will focus on the mode of failure of the exocarp (fracture along vs. across cell walls) and the relationship between failure thresholds and morphometric characteristics of the exocarp. However, when Pfruit und Pcell are low, the hypothesis of Pfruit driven strain cracking must be rejected and the mechanistic basis for low pressures (presence of apoplastic solutes) clarified on a temporal (in the course of development) and a spatial scale (exocarp vs. mesocarp). We focus on sweet cherry, because detailed information on this species and experience in extending the short harvest period is available. Where appropriate, other cracking susceptible species (sour cherry, plum, Vaccinium, Ribes, tomato) will be included to further extend the experimental period and to maximize the range in intrinsic cracking susceptibility.
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