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  • 1
    Language: English
    In: Soil Biology and Biochemistry, 2011, Vol.43(8), pp.1738-1741
    Description: Understanding the turnover of organic matter (OM) in soils necessitates information on biological stability and ecological functions. For easy characterization of slowly cycling OM, treatments using oxidants such as sodium hypochlorite (NaOCl) have been applied. The rationale for that approach is, however, questionable and concerns exist to which extent abiotic oxidation can mimic biological mineralization. Here we compare biological mineralization of mineral-bound OM to its resistance to chemical oxidation by 6 mass% NaOCl. Water-extractable OM, sorbed to goethite, vermiculite, and pyrophyllite at pH 4.0 and in different background electrolytes (CaCl , NaCl, NaCl–NaH PO ) to favor or exclude certain binding mechanisms, was subsequently subjected to NaOCl treatment (pH 7, either for 18 or 6 × 6 h). Irrespective of mineral surface properties and mechanisms involved in OM sorption, NaOCl removed a constant portion of the sorbed OC. More OC survived when bound to goethite than to vermiculite, thus confirming previous results on the increase of oxidation-resistant OC with increasing Fe and Al (hydr)oxide contents in different soils. Mineralizable OC (within 90 days) was much smaller than the NaOCl-removable OC and both fractions were negatively correlated (  = 0.90 for the 18 h treatment;  = 0.86 for the 6 × 6 h treatment), suggesting that chemically oxidizable OM does not represent the portion of sorbed OM available to biological consumption. ► Organic matter resistant to wet oxidation has been considered a biologically stable fraction. ► The OC fraction in mineral−organic associations oxidizable by sodium hypochlorite was inversely related to the mineralizable OC fraction. ► Organic matter resistant to chemical oxidation cannot be used as proxy for biologically stable OM.
    Keywords: Sodium Hypochlorite ; Naocl ; Wet Oxidation ; Organic Matter ; Stabilization ; Passive Organic Matter Pool ; Stable Organic Matter ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, September 2012, Vol.52, pp.29-32
    Description: Dissolved organic matter has been recognized as mobile, thus crucial to translocation of metals, pollutants but also of nutrients in soil. We present a conceptual model of the vertical movement of dissolved organic matter with soil water, which deviates from the view of a chromatographic stripping along the flow path. It assumes temporal immobilization (sorptive or by co-precipitation), followed by microbial processing, and re-release (by desorption or dissolution) into soil water of altered compounds. The proposed scheme explains well depth trends in age and composition of dissolved organic matter as well as of solid-phase organic matter in soil. It resolves the paradox of soil organic matter being oldest in the youngest part of the soil profile – the deep mineral subsoil. ► Improved conceptual model of DOM movement in soil. ► Physico-chemical immobilization by sorption and/or co-precipitation. ► Microbial processing of sorbed/co-precipitated matter, subsequent re-release (desorption/dissolution) of altered compounds. ► DOM mirrors soil organic matter. ► Model explains changes in soil organic matter properties with depth.
    Keywords: Adsorption ; Conceptual Model ; Co-Precipitation ; Dissolved Organic Matter ; Microbial Processing ; Soil Organic Matter ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    In: PLoS ONE, 2014, Vol.9(2)
    Description: Temperate forests are assumed to be organic carbon (OC) sinks, either because of biomass increases upon elevated CO 2 in the atmosphere and large nitrogen deposition, or due to their age structure. Respective changes in soil OC and total nitrogen (TN) storage have rarely been proven. We analysed OC, TN, and bulk densities of 100 soil cores sampled along a regular grid in an old-growth deciduous forest at the Hainich National Park, Germany, in 2004 and again in 2009. Concentrations of OC and TN increased significantly from 2004 to 2009, mostly in the upper 0–20 cm of the mineral soil. Changes in the fine earth masses per soil volume impeded the detection of OC changes based on fixed soil volumes. When calculated on average fine earth masses, OC stocks increased by 323±146 g m −2 and TN stocks by 39±10 g m −2 at 0–20 cm soil depth from 2004 to 2009, giving average annual accumulation rates of 65±29 g OC m −2 yr −1 and 7.8±2 g N m −2 yr −1 . Accumulation rates were largest in the upper part of the B horizon. Regional increases in forest biomass, either due to recovery of forest biomass from previous forest management or to fertilization by elevated CO 2 and N deposition, are likely causes for the gains in soil OC and TN. As TN increased stronger (1.3% yr −1 of existing stocks) than OC (0.9% yr −1 ), the OC-to-TN ratios declined significantly. Results of regression analyses between changes in OC and TN stocks suggest that at no change in OC, still 3.8 g TN m −2 yr −1 accumulated. Potential causes for the increase in TN in excess to OC are fixation of inorganic N by the clay-rich soil or changes in microbial communities. The increase in soil OC corresponded on average to 6–13% of the estimated increase in net biome productivity.
    Keywords: Research Article ; Agriculture ; Biology ; Chemistry ; Earth Sciences
    E-ISSN: 1932-6203
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, December 2013, Vol.67, pp.133-139
    Description: Dissolved organic matter (DOM) plays a fundamental role for many soil processes. For instance, production, transport, and retention of DOM control properties and long-term storage of organic matter in mineral soils. Production of water-soluble compounds during the decomposition of plant litter is a major process providing DOM in soils. Herein, we examine processes causing the commonly observed increase in contribution of aromatic compounds to WSOM during litter decomposition, and unravel the relationship between lignin degradation and the production of aromatic WSOM. We analysed amounts and composition of water-soluble organic matter (WSOM) produced during 27 months of decomposition of leaves and needles (ash, beech, maple, spruce, pine). The contribution of aromatic compounds to WSOM, as indicated by the specific UV absorbance of WSOM, remained constant or increased during decomposition. However, the contribution of lignin-derived compounds to the total phenolic products of C-labelled tetramethylammonium hydroxide ( C-TMAH thermochemolysis increased strongly (by 〉114%) within 27 months of decomposition. Simultaneous changes in contents of lignin phenols in solid litter residues (cupric oxide method as well as C-TMAH thermochemolysis) were comparably small (−39% to +21% within 27 months). This suggests that the increasing contribution of lignin-derived compounds to WSOM during decomposition does not reflect compositional changes of solid litter residues, but rather the course of decomposition processes. In the light of recently published findings, these processes include: (i) progressive oxidative alteration of lignin that results in increasing solubility of lignin, (ii) preferential degradation of soluble, non-lignin compounds that limits their contribution to WSOM during later phases of decomposition.
    Keywords: Dissolved Organic Matter ; Water Soluble Organic Matter ; Litter Decomposition ; Lignin Degradation ; 13c-Tmah Thermochemolysis ; Litter Bag Experiment ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Biogeochemistry, 1 February 2012, Vol.107(1/3), pp.409-422
    Description: In the last decades, in particular forest ecosystems became increasingly N saturated due to elevated atmospheric N deposition, resulting from anthropogenic N emission. This led to serious consequences for the environment such as N leaching to the groundwater. Recent efforts to reduce N emissions raise the question if, and over what timescale, ecosystems recover to previous conditions. In order to study the effects on N distribution and N transformation processes under the lowered N deposition treatment, we investigated the fate of deposited NH₄⁺ -¹⁵N in soil of a N-saturated Norway spruce forest (current N deposition: 34 kg ha⁻¹ year⁻¹ ; critical N load: 14 kg ha⁻ ¹year⁻ ¹), where N deposition has been reduced to 11.5 kg ha⁻¹ year⁻¹ since 14.5 years. We traced the deposited ¹⁵N in needle litter, bulk soil, and amino acids, microbial biomass and inorganic N in soil. Under reduced N deposition, 123 ± 23% of the deposited N was retained in bulk soil, while this was only 72 ± 15% under ambient deposition. We presume that with reduced deposition the amount of deposited N was small enough to become completely immobilized in plant and soil and no leaching losses occurred. Trees receiving reduced N deposition showed a decline in N content as well as in ¹⁵N incorporation into needle litter, indicating reduced N plant uptake. In contrast, the distribution of ¹⁵N within the soil over active microbial biomass, microbial residues and inorganic N was not affected by the reduced N deposition. We conclude that the reduction in N deposition impacted only plant uptake and drainage losses, while microbial N transformation processes were not influenced. We assume changes in the biological N turnover to start with the onset of the decomposition of the new, N-depleted litter.
    Keywords: Biology ; Geology ; Chemistry;
    ISSN: 01682563
    E-ISSN: 1573515X
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  • 6
    Language: English
    In: Biogeochemistry, 2012, Vol.107(1), pp.409-422
    Description: In the last decades, in particular forest ecosystems became increasingly N saturated due to elevated atmospheric N deposition, resulting from anthropogenic N emission. This led to serious consequences for the environment such as N leaching to the groundwater. Recent efforts to reduce N emissions raise the question if, and over what timescale, ecosystems recover to previous conditions. In order to study the effects on N distribution and N transformation processes under the lowered N deposition treatment, we investigated the fate of deposited NH 4 + - 15 N in soil of a N-saturated Norway spruce forest (current N deposition: 34 kg ha −1  year −1 ; critical N load: 14 kg ha −1  year −1 ), where N deposition has been reduced to 11.5 kg ha −1  year −1 since 14.5 years. We traced the deposited 15 N in needle litter, bulk soil, and amino acids, microbial biomass and inorganic N in soil. Under reduced N deposition, 123 ± 23% of the deposited N was retained in bulk soil, while this was only 72 ± 15% under ambient deposition. We presume that with reduced deposition the amount of deposited N was small enough to become completely immobilized in plant and soil and no leaching losses occurred. Trees receiving reduced N deposition showed a decline in N content as well as in 15 N incorporation into needle litter, indicating reduced N plant uptake. In contrast, the distribution of 15 N within the soil over active microbial biomass, microbial residues and inorganic N was not affected by the reduced N deposition. We conclude that the reduction in N deposition impacted only plant uptake and drainage losses, while microbial N transformation processes were not influenced. We assume changes in the biological N turnover to start with the onset of the decomposition of the new, N-depleted litter.
    Keywords: Amino acids ; Microbial biomass ; N deposition ; N tracer ; Solling roof project
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 7
    Language: English
    In: Chemosphere, 1999, Vol.38(14), pp.3237-3245
    Description: The use of probabilistic neural networks (PNN) to model the acute toxicity (96 h LC50) to the fathead minnow (Pimephales promelas), based on 865 chemical data sets, is described. The octanol/water partition co-efficient was not used as an input parameter and the information fed into the PNN was solely based on simple molecular descriptors that could be derived from the chemical structure. An extensive list of functional group descriptors is provided and the development of a model and cross validation procedures is explained. Predictions resulted from procedures involved in 5 subsets, each containing 20 per cent of the data, and compared to measured (expected) output data. High values of the correlations between the measured and predicted values strongly suggested the use of linear correlation to improve the model. The excellent statistics obtained with the PNN model indicate its applicability to a great variety of compounds.
    Keywords: Fathead Minnow ; Acute Toxicity ; Neural Network ; Model ; Prediction ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 8
    Language: English
    Description: Each volume in the series focuses on a particular taxon, presenting detailed and reliable ecotoxicological results from both laboratory and field experiments, performed for a comprehensive range of chemicals. A taxonomical guide to the species is given, together with relevant biological and ecological information.In recent times much attention has been focused on the effects of anthropogenic emissions of chemicals. This series is unique in providing a considered estimate of the potential impact of such chemicals on the environment.
    Keywords: Water Quality Bioassay ; Water -- Pollution -- Toxicology ; Water -- Pollution -- Testing ; Photobacterium Phosphoreum ; Microbiological Assay ; Bioluminescence Assay ; Science;
    ISBN: 9781315094694
    ISBN: 9782881249747
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  • 9
    Language: English
    In: Soil Biology and Biochemistry, January 2019, Vol.128, pp.22-34
    Description: Phosphorus (P) is a key nutrient but still we have a limited knowledge on the controls of mobilization and fluxes of P in forest soils. Our study explored the linkages between P mobilization in organic horizons and mineral soils and the P status of soils, as affected by two consecutive drying and rewetting (D/W) cycles. We sampled litter layers (Oi), mixed Oe-Oa horizons, and A horizons in three beech forests along a P availability gradient in Germany. Carbon mineralization and release of dissolved organic matter (DOC, DOP) and dissolved inorganic P (DIP) were studied in microcosms exposed to an initial harsh drying (40 °C for 72 h) and a moderate dry spell (1 month at 20 °C). In Oi horizons, net P mineralization decreased with decreasing P status despite a similar C mineralization at all sites. This supports the general concept that the stoichiometric difference between substrate and microbial biomass primarily drives P release from decomposing organic matter. Counterintuitively, P mobilization per unit soil P increased towards P-poor sites in the mineral soil, likely due to decreasing contents of reactive secondary minerals and the consequently smaller P sorption. Drying and rewetting caused stronger mobilization of DIP and DOP (+108% on average) than of DOC (+51%). The parallel decline in specific UV absorptivity of DOM suggests that lysis of microbial cells drove the drought-induced P release. The D/W effects on P mobilization were particularly strong in P-poor soils, where greater portions of P are bound to microbial biomass, which are prone to become released upon rewetting. Since mobilized P can potentially be leached from soils, our findings indicate, that drought-induced P mobilization fosters the progressive P depletion of already P-poor soils. The possible P leaching losses from mineral soils seem rather be driven by soil mineralogy than by P status.
    Keywords: P Status ; P Availability Gradient ; P Mineralization ; Stoichiometry ; C:P Ratio ; Dop ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 10
    Language: English
    In: Chemosphere, 1983, Vol.12(9), pp.1159-1167
    Description: An investigation is described of the effects of increasing halogen substitution on octanol/water partition coefficients of a variety of aromatic and heterocyclic parent molecules. It is suggested that the increasing chlorine substitution of compounds such as benzene, aniline, pyridine and diphenyl results in declining increases of the octanol/water partition coefficients. Two equations are derived which allow the quick estimation of the partition coefficient of any congener from the known value of another. These equations are of particular value for compounds the partition coefficients of which are difficult to determine experimentally, for the prediction of their environmental fates and bioaccumulation potentials and for their toxicities, which often correlate with their partition coefficients.
    Keywords: Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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