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  • Springer (CrossRef)  (11)
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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: Paddy and Water Environment, 2018, Vol.16(2), pp.243-252
    Description: Silicon (Si) mitigates abiotic and biotic stresses for rice plants ( Oryza sativa L.). Here, we test relationships between Si cycling, plant growth, and pest and fungal attacks in rice agroecosystems. We conducted a plot experiment on Si fertilization in a Southern Vietnamese paddy, where plant-available Si was inherently low. For two cropping seasons, we investigated the temporal dynamics of Si in soil solution, plant Si uptake, and the occurrence of leaf folders ( Cnaphalocrocis medinalis ) and rice blast caused by the fungus Magnaporthe oryzae . Silicon application increased Si concentrations in soil solutions collected in the field as expected from previous laboratory experiments. Soil solution Si concentrations were furthermore affected by Si uptake by plants and by recycling Si with rice straw ash. Silicon concentrations in rice leaves at tillering stage increased with increasing Si application. However, surprisingly, no relationship between Si in soil solution and Si concentration in straw at maturity stage was found. The occurrences of leaf folders and rice blast disease were mitigated by increased Si uptake. However, rice biomass production was not affected, probably because the biotic stress level was generally low. Our field data emphasize the importance of recycling crop residues in rice fields for the Si supply to plants, especially in regions with low Si availability. They furthermore show that under field conditions, the relationship between dissolved Si in soil solution and Si uptake by rice plants is not as straightforward as expected and thus needs to be further investigated.
    Keywords: Dissolved silicon ; Leaf folder ; Rice ; Rice blast ; Silicon fertilization
    ISSN: 1611-2490
    E-ISSN: 1611-2504
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  • 5
    Language: English
    In: Paddy and Water Environment, 2018, Vol.16(2), pp.353-358
    Description: Two major human-made problems in rice production systems in the north of Vietnam concern the low plant-available silicon content of soils and the low biodiversity. The results of the LEGATO project suggest a change to an environmentally friendly rice production system that will help to recover biodiversity. We propose here a framework for a demonstration and dissemination model that will be exemplary for the farmers once it has been successfully realized. We advocate local-option models in different districts to demonstrate to farmers. The methods should be adapted to local and ecoregional differences in climate and land-use tradition, and they explicitly take into account soil care, organic fertilizer, manual weeding, native nectar-rich plant bunds, manual pest snail collection, hymenopteran nesting aids, and biodiversity and yield monitoring.
    Keywords: Biodiversity ; Silicon ; Rice field ; North Vietnam
    ISSN: 1611-2490
    E-ISSN: 1611-2504
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  • 6
    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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  • 7
    Language: German
    In: Forstwissenschaftliches Centralblatt, 1930, Vol.52(19), pp.761-774
    Keywords: Life Sciences ; Forestry ; Plant Sciences ; Plant Ecology ; Agriculture ; Forestry;
    ISSN: 0015-8003
    E-ISSN: 1439-0337
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  • 8
    Language: German
    In: Forstwissenschaftliches Centralblatt, 1930, Vol.52(20), pp.810-818
    Keywords: Life Sciences ; Forestry ; Plant Sciences ; Plant Ecology ; Agriculture ; Forestry;
    ISSN: 0015-8003
    E-ISSN: 1439-0337
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  • 9
    Language: English
    In: Biogeochemistry, 2019, Vol.143(1), pp.31-54
    Description: Submerged rice cultivation is characterized by redox fluctuations and results in the formation of paddy soils, often accompanied by soil organic carbon (SOC) accumulation. The impact of redox fluctuations and the underlying soil type on the fate of organic carbon (OC) in paddy soils are unknown. Hence, we mimicked paddy soil development in the laboratory by exposing two soil types with contrasting mineral assemblages (Alisol and Andosol) to eight anoxic–oxic cycles over 1 year. Soils regularly received 13 C-labeled rice straw. As control we used a second set of samples without straw addition as well as samples under static oxic conditions with and without straw. Headspaces were analyzed for carbon dioxide and methane as well as their δ 13 C signatures, whereas soil solutions were analyzed for redox potential, pH, dissolved iron, and dissolved organic carbon (DOC and DO 13 C). At the end of the experiment, when eight redox cycles were completed, mineral-associated organic matter (MOM) was isolated by density fractionation and characterized for δ 13 C, non-cellulosic carbohydrates, and lignin-derived phenols. Moreover, changes in the soil’s microbial community structure were measured. For both soil types, headspace data confirmed less respiration in straw-amended soils with redox fluctuation than in those under static oxic conditions. The δ 13 C data revealed that, irrespective of soil type, straw carbon allocation into MOM was larger in soils with redox fluctuation than in those with static oxic conditions. A net increase in MOM after the one-year incubation, however, was only observed in the respective Andosol, probably due to abundant reactive minerals capable of OC uptake. In the Alisol, straw OC most likely exchanged initial MOM. A potential for lignin accumulation in the MOM of soils incubated with straw and redox fluctuation was observed for both soil types. Lignin and carbohydrates suggest a plant origin of MOM formed under redox fluctuation. The initially similar bacterial community composition of the Alisol and Andosol changed differently under redox fluctuation. The stronger change in the Alisol indicates less protective microbial habitats. In summary, the overall turnover of straw OC in soils under redox fluctuation seems to be independent of soil type, while net accumulation of SOC as well as the evolution of the bacterial community structure may in part depend on soil type, suggesting an impact of the soil’s mineral composition.
    Keywords: Microbial community ; Mineral-associated organic matter ; Mineralization ; Paddy soils ; Redox fluctuation ; Soil organic matter formation
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 10
    Language: English
    In: Journal of Neurology, 2001, Vol.248(12), pp.1101-1103
    Description: Byline: Klaus Jahn (1), Kathrin Winkler (1), Reinhold Tiling (2), Thomas Brandt (1) Author Affiliation: (1) Ludwig-Maximilians University, Department of Neurology, Klinikum Grosshadern, Marchioninistrasse 15, 81377 Munchen, Germany, Tel.: +49-89/7095-2585, Fax: +49-89/7095-5584, E-Mail: Klaus.Jahn@lrz.uni-muenchen.de, DE (2) Department of Nuclear Medicine, DE Article note: Received: 11 April 2001, Received in revised form: 18 June 2001, Accepted: 4 July 2001
    Keywords: Intracranial Hypertension -- Causes Of ; Fistulas -- Complications And Side Effects ; Fistulas -- Research ; Diskectomy -- Complications And Side Effects;
    ISSN: 0340-5354
    E-ISSN: 1432-1459
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