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Berlin Brandenburg

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  • 1
    Language: English
    In: Plant and Soil, 2010, Vol.330(1), pp.481-501
    Description: A modelling approach was used to extend the knowledge about the processes that affect the availability of the nutrient P and the toxic agent As V in the rhizosphere in the presence of a strong sorbent. Based on compartment system experiments in which Zea mays was grown the following hypothesis were assumed: a) measured P concentration gradients can be explained by the mobilisation of P by the root exudate citrate, and b) measured As V concentration gradients can be explained by the simultaneous effect of the competitive sorption of As V and P and the competitive uptake of As V and P. First, the feasibility of the applied description of soil chemical processes was justified. Then competitive uptake was implemented in the computer code using two different mathematical approaches. Our model calculation provided support for hypothesis a) and suggested that hypothesis b) has to be extended. The results show that the competitive uptake of As V and P has an influence on As V concentrations in the rhizosphere, but including competitive uptake was not sufficient to predict observed As V concentration profiles. Recent results on plant As-metabolism like As III efflux and Si As III interaction probably have to be included in addition for simulation of measured As V concentration profiles.
    Keywords: Rhizosphere ; Modelling ; Speciation ; Phosphate ; Arsenate ; Goethite
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Language: English
    In: Plant and Soil, 2004, Vol.258(1), pp.307-327
    Description: Soil solution composition changes with time and distance from the root surface as a result of mass flow, diffusion, plant nutrient uptake and root exudation. A model system was designed, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). K + concentration in the rhizosphere soil solution decreased during the initial growth stage (12 days after planting, DAP). Thereafter K + accumulated with time, due to mass flow as the dominating process. The extend of K + accumulation depended on the initial fertiliser application. As K + concentrations in soil solution increase, not only as a result of transport exceeding uptake, but also as a result of decreasing soil water content, it is hypothesised that K concentration in soil solution is not the only trigger for the activity of K transporters in membranes, but ABA accumulation in roots induced by decreasing soil matric potentials may add to the regulation. A strong decrease of rhizosphere pH with time is observed as a result of H + efflux from the roots in order to maintain cation-anion balance. In addition the K + to Ca 2+ ratio was altered continuously during the growing period, which has an impact on Ca 2+ uptake and thus firmness of cell walls, apoplast pH, membrane integrity and activity of membrane transporters. The value of osmotic potential in the rhizosphere soil solution increased with time indicating decreasing soil water availability. Modelling approaches based on the data obtained with the system might help to fill in the time gaps caused by the low temporal resolution of soil solution sampling method.
    Keywords: K ; matric potential ; osmotic potential ; pH ; rhizosphere ; soil solution
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 3
    Language: English
    In: Plant and Soil, 1 October 2013, Vol.371(1/2), pp.267-279
    Description: Aims and background Release of 'non-exchangeable' potassium (K) from interlayers of illite is diffusioncontrolled and has been shown to depend on the solution concentration of Ê and other cations (Ca²⁺, Mg²⁺, NH₄⁺). Methods We analysed changes in soil solution concentrations of K and competing cations in situ at different distances from the root surface over time and related them to the transformation of illite, as revealed by X-ray diffraction, and chemical measures of differently bound K. Results and Conclusions Within 49 and 98 days, respectively, 6.4 and 14.4 % of the illite's total K was released upon contact with the root system. Mixed layered minerals increased from 33 (0 d) to 35 (49 d) to 40 % (98 d). Release of K from interlayers and the transformation of illite occurred at soil solution K concentrations close to the threshold of 80 µM suggested earlier. Concentrations of Ca and Mg increased with decreasing distance from the root surface, promoting the release of K. The NaBPh₄ method supposed to determine 'non-exchangeable' K extracted only 1/3 of the total K from illite.
    Keywords: Physical sciences -- Earth sciences -- Geology ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Biology -- Botany ; Physical sciences -- Earth sciences -- Geology ; Physical sciences -- Chemistry -- Chemical elements ; Biological sciences -- Biology -- Botany ; Biological sciences -- Agriculture -- Agricultural sciences ; Physical sciences -- Earth sciences -- Geology
    ISSN: 0032079X
    E-ISSN: 15735036
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  • 4
    Language: English
    In: Biogeochemistry, 2006, Vol.77(1), pp.25-56
    Description: Soil organic matter (OM) can be stabilized against decomposition by association with minerals, by its inherent recalcitrance and by occlusion in aggregates. However, the relative contribution of these factors to OM stabilization is yet unknown. We analyzed pool size and isotopic composition ( 14 C, 13 C) of mineral-protected and recalcitrant OM in 12 subsurface horizons from 10 acidic forest soils. The results were related to properties of the mineral phase and to OM composition as revealed by CPMAS 13 C-NMR and CuO oxidation. Stable OM was defined as that material which survived treatment of soils with 6 wt% sodium hypochlorite (NaOCl). Mineral-protected OM was extracted by subsequent dissolution of minerals by 10% hydrofluoric acid (HF). Organic matter resistant against NaOCl and insoluble in HF was considered as recalcitrant OM. Hypochlorite removed primarily 14 C-modern OM. Of the stable organic carbon (OC), amounting to 2.4–20.6 g kg −1 soil, mineral dissolution released on average 73%. Poorly crystalline Fe and Al phases (Fe o , Al o ) and crystalline Fe oxides (Fe d−o ) explained 86% of the variability of mineral-protected OC. Atomic C p /(Fe+Al) p ratios of 1.3–6.5 suggest that a portion of stable OM was associated with polymeric Fe and Al species. Recalcitrant OC (0.4–6.5 g kg −1 soil) contributed on average 27% to stable OC and the amount was not correlated with any mineralogical property. Recalcitrant OC had lower Δ 14 C and δ 13 C values than mineral-protected OC and was mainly composed of aliphatic (56%) and O-alkyl (13%) C moieties. Lignin phenols were only present in small amounts in either mineral-protected or recalcitrant OM (mean 4.3 and 0.2 g kg −1 OC). The results confirm that stabilization of OM by interaction with poorly crystalline minerals and polymeric metal species is the most important mechanism for preservation of OM in these acid subsoil horizons.
    Keywords: C isotopes ; Hydrofluoric acid ; Lignin ; Recalcitrant organic matter ; Sodium hypochlorite ; Stable organic matter
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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