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Berlin Brandenburg

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  • Phosphates
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  • 1
    In: Canadian Journal of Forest Research (Revue canadienne de recherche forestière), 2000, Vol.30(7), pp.1034-1040
    Description: Molybdenum plays an important role in the nitrogen turnover of ecosystems. However, very little is known about Mo availability in forest soils. We measured the oxalate-extractable Mo concentrations of acid forest soils, the Mo, nitrate, phosphate, and sulfate fluxes from the organic forest floor into the mineral soil using resin tubes and the Mo concentrations of the tree needles at 28 different Norway spruce ( Picea abies (L.) Karst.) sites in southern Germany. The supply of oxalate-extractable Mo varied from 51 to 3400 gha -1 , with the lowest values occurring in sandstone-derived soils (370 212 gha -1 ; mean SD). Molybdenum concentrations of current-year needles were in the range of 5 to 48 ngg -1 . The Mo needle concentrations and oxalate-extractable Mo of soils did not correlate. However, Mo fluxes (6-60 gha -1 a -1 ) from the organic forest floor into the mineral soils were correlated to needle concentrations and to the NO 3 fluxes. We conclude that Mo turnover within forest ecosystems is governed by Mo plant availability of mineral soils as well as by plant Mo uptake. In addition, Mo cycling strongly affects Mo distribution within soil profiles and Mo fluxes out of the organic layer.
    Description: Le molybdne joue un rle important dans le renouvellement de l'azote des cosystmes. Toutefois, on connat peu de choses au sujet de la disponibilit de Mo dans les sols forestiers. Nous avons mesur la concentration de Mo extractible l'oxalate dans des sols forestiers acides, les flux de Mo, de nitrate, de phosphate et de sulfate, de la couverture morte organique vers le sol minral, l'aide de tubes de rsines ainsi que la concentration de Mo dans les aiguilles d'pica commun ( Picea abies (L.) Karst.) dans 28 sites diffrents du sud de l'Allemagne. L'apport de Mo extractible l'oxalate variait de 51 3400 gha -1 avec les plus faibles valeurs provenant des sols drivs de grs (370 212 gha -1 ; moyenne ET). La concentration de Mo dans les aiguilles de l'anne courante variait de 5 48 ngg -1 . La concentration de Mo dans les aiguilles et le Mo extractible l'oxalate dans les sols n'taient pas corrls. Toutefois, les flux de Mo (6-60 gha -1 a -1 ) de la couverture morte organique vers le sol minral taient corrls aux concentrations foliaires et aux flux de NO 3 . Nous en concluons que le renouvellement de Mo dans les cosystmes forestiers est gouvern par le Mo des sols minraux disponible pour la plante autant que par le prlvement de Mo par la plante. De plus, le recyclage de Mo affecte fortement la distribution de Mo dans les profils de sol et le flux de Mo hors de la couche organique.[Traduit par la Rdaction]
    Keywords: Forest Floor ; Soils (Acid) ; Mobility ; Soil Profiles ; Molybdenum ; Minerals ; Nitrogen ; Sulfate ; Picea Abies ; Management and Conservation;
    ISSN: 0045-5067
    E-ISSN: 1208-6037
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 2006, Vol.70(3), pp.595-607
    Description: Anions of polycarboxylic low-molecular-weight organic acids (LMWOA) compete with phosphate for sorption sites of hydrous Fe and Al oxides. To test whether the sorption of LMWOA anions decreases the accessibility of micropores (〈2 nm) of goethite (α-FeOOH) for phosphate, we studied the kinetics of citrate-induced changes in microporosity and the phosphate sorption kinetics of synthetic goethite in the presence and absence of citrate in batch systems for 3 weeks (500 μM of each ion, pH 5). We also used C-coated goethite obtained after sorption of dissolved organic matter in order to simulate organic coatings in the soil. We analyzed our samples with N adsorption and electrophoretic mobility measurements. Citrate clogged the micropores of both adsorbents by up to 13% within 1 h of contact. The micropore volume decreased with increasing concentration and residence time of citrate. In the absence of citrate, phosphate diffused into micropores of the pure and C-coated goethite. The C coating (5.6 μmol C m ) did not impair the intraparticle diffusion of phosphate. In the presence of citrate, the diffusion of phosphate into the micropores of both adsorbents was strongly impaired. We attribute this to the micropore clogging and the ligand-induced dissolution of goethite by citrate. While the diffusion limitation of phosphate by citrate was stronger when citrate was added before phosphate to pure goethite, the order of addition of both ions to C-coated goethite had only a minor effect on the intraparticle diffusion of phosphate. Micropore clogging and dissolution of microporous hydrous Fe and Al oxides may be regarded as potential strategies of plants to cope with phosphate deficiency in addition to ligand-exchange.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2017, Vol.180(2), pp.220-230
    Description: Standard procedures to assess P availability in soils are based on batch experiments with various extractants. However, in most soils P nutrition is less limited by bulk stocks but by strong adsorption and transport limitation. The basic principle of root‐phosphate uptake is to strip phosphate locally from the solid phase by forming a radial depletion zone in the soil solution, optionally enhanced by release of mobilizing substances. Microdialysis (MD), a well‐established method in pharmacokinetics, is capable to mimic important characteristics of P root uptake. The sampling is by diffusional exchange through a semipermeable membrane covering the probes with their sub‐mm tubular structure. Additionally, the direct environment of the probe can be chemically modified by adding, ., carboxylates to the perfusate. This study is the first approach to test the applicability of MD in assessing plant available phosphate in soils and to develop a framework for its appropriate use.We used MD in stirred solutions to quantify the effect of pumping rate, concomitant ions, and pH value on phosphate recovery. Furthermore, we measured phosphate yield of top‐soil material from a beech forest, a non‐fertilized grassland, and from a fertilized corn field. Three perfusates have been used based on a 1 mM KNO solution: pure (1), with 0.1 mM citric acid (2), and with 1 mM citric acid (3). Additionally, a radial diffusion model has been parametrized for the stirred solutions and the beech forest soil.Results from the tests in stirred solutions were in good agreement with reported observations obtained for other ionic species. This shows the principal suitability of the experimental setup for phosphate tests. We observed a significant dependency of phosphate uptake into the MD probes on dialysate pumping rate and on ionic strength of the outside solution. In the soils, we observed uptake rates of the probes between 1.5 × 10 and 6.7 × 10 mol s cm in case of no citrate addition. Surprisingly, median uptake rates were mostly independent of the bulk soil stocks, but the P‐fertilized soil revealed a strong tailing towards higher values. This indicates the occurrence of hot P spots in soils. Citrate addition increased P yields only in the higher concentration but not in the forest soil. The order of magnitude of MD uptake rates from the soil samples matched root‐length related uptake rates from other studies. The micro‐radial citrate release in MD reflects the processes controlling phosphate mobilization in the rhizosphere better than measurements based on “flooding” of soil samples with citric acid in batch experiments. Important challenges in MD with phosphate are small volumes of dialysate with extremely low concentrations and a high variability of results due to soil heterogeneity and between‐probe variability. We conclude that MD is a promising tool to complement existing P‐analytical procedures, especially when spatial aspects or the release of mobilizing substances are in focus.
    Keywords: Plant Availability ; Diffusion Limitation ; Spatial Heterogeneity ; Carboxylates
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Geoderma, 01 July 2017, Vol.297, pp.61-69
    Description: The use of heavy machinery for timber harvesting causes soil damage, which may restrict forest soil functions over decades. Numerous studies have demonstrated the negative impact of soil compaction on soil physical properties, but the effects of compaction of forest soils on soil chemical and biological processes like the phosphorus availability are largely unknown. Aim of our study was to analyze the effect of skidding activity on the P dynamics on skid trails and the soil recovery ability after skidding. Furthermore, we wanted to assess if acid phosphatase activity is an appropriate indicator of soil structure damage after compaction. We investigated the phosphorus availability, acid phosphatase activity, TOC, pH value, and fine root density of soil samples from skid trails and from control plots without any skidding effect. We conducted our studies at three sites (Göttingen: Cambisols on limestone, Heide: Podzol on glacial drift and sand, and Solling: Cambisols at loess-covered sandstone) in Lower Saxony, Germany 10 to 40 years after last traffic impact in a space-for-time substitution. We observed mainly higher P concentrations and higher pH values at the wheel tracks than in the control. TOC was predominantly higher at the wheel tracks, but lower TOC at the wheel tracks was also found. In the acidic loams of the Solling region, the amount of mineralized phosphate was much higher in the tracks compared to the control areas 10 to 30 years after last traffic impact. This suggests a decoupling of P mineralization from P uptake in the wheel tracks for several decades. Furthermore, higher as well as lower phosphatase activity at the wheel tracks compared to the untrafficked control was found, but higher phosphatase activities at the wheel tracks were predominant. Acid phosphatase activity was strongly correlated with TOC, but did not correlate with the time since last traffic impact and the gas diffusivity of the soil. Therefore, our results did not confirm that acid phosphatase activity is an appropriate soil biological indicator of soil compaction and structural recovery.
    Keywords: Acid Phosphatase Activity ; P Availability ; Soil Compaction ; Soil Structure Recovery ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    Language: English
    In: Geochimica et Cosmochimica Acta, 2006, Vol.70(12), pp.2957-2969
    Description: Hydration of organic coatings in soils is expected to affect the sorption of oxyanions onto hydrous Fe and Al oxides. We hypothesized that the hydration of polygalacturonate (PGA) coatings on alumina (Al O ) increases their permeability for phosphate. Pure and PGA-coated alumina were equilibrated in deionized water for 2 and 170 h at pH 5 and 20 °C before studying (i) their porosity with N gas adsorption and H NMR relaxometry, (ii) structural changes of PGA-coatings with differential scanning calorimetry (DSC), and (iii) the kinetics of phosphate sorption and PGA desorption in batch experiments. Scanning electron micrographs revealed that PGA molecules formed three-dimensional networks with pores ranging in size from 〈10 to several hundred nanometers. Our NMR results showed that the water content of intraparticle alumina pores decreased upon PGA sorption, indicating a displacement of pore water by PGA. The amount of water in interparticle alumina pores increased strongly after PGA addition, however, and was attributed to water in pores of PGA and/or in pores at the PGA-alumina interface. The flexibility of PGA molecules and the fraction of a PGA gel phase increased within one week of hydration, implying restructuring of PGA. Hydration of PGA coatings increased the amount of phosphate defined as instantaneously sorbed by 84%, showing that restructuring of PGA enhanced the accessibility of phosphate to external alumina surfaces. Despite the fact that the efficacy of phosphate to displace PGA was higher after 170 h than after 2 h, a higher phosphate surface loading was required after 170 h to set off PGA desorption. Our findings imply that the number of PGA chain segments directly attached to the alumina surface decreased with time. We conclude that hydration/dehydration of polymeric surface coatings affects the sorption kinetics of oxyanions, and may thus control the sorption and transport of solutes in soils.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 6
    In: Environmental Microbiology, June 2016, Vol.18(6), pp.1988-2000
    Description: Phosphorus () is an important macronutrient for all biota on earth but similarly a finite resource. Microorganisms play on both sides of the fence as they effectively mineralize organic and solubilize precipitated forms of soil phosphorus but conversely also take up and immobilize . Therefore, we analysed the role of microbes in two beech forest soils with high and low content by direct sequencing of metagenomic deoxyribonucleic acid. For inorganic solubilization, a significantly higher microbial potential was detected in the ‐rich soil. This trait especially referred to  olibacter usiatus, likewise one of the dominating species in the data sets. A higher microbial potential for efficient phosphate uptake systems () was detected in the ‐depleted soil. Genes involved in starvation response regulation (, ) were prevalent in both soils. This underlines the importance of effective phosphate (ho) regulon control for microorganisms to use alternative sources during phosphate limitation. Predicted genes were primarily harboured by hizobiales, ctinomycetales and cidobacteriales.
    Keywords: Soil Microbiology – Analysis ; Nucleic Acids – Analysis ; Phosphates – Analysis ; Forest Soils – Analysis ; Soil Phosphorus – Analysis;
    ISSN: 1462-2912
    E-ISSN: 1462-2920
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  • 7
    Language: English
    In: Soil Science Society of America Journal, Sept-Oct, 2006, Vol.70(5), p.1731(10)
    Description: Uronates are important constituents of maize mucilage and polyuronates are used as a simplified model of the soil--root interface. We tested whether galacturonate (GA) and polygalacturonate (PGA) impair the diffusion of phosphate (P[O.sub.4]) into and out of pores of a synthetic goethite (147 [m.sup.2] [g.sup.-1]) and whether the effect of maize mucigel (MU) is comparable to PGA. We measured the P[O.sub.4] desorption kinetics of goethites in batch experiments over 2 wk at pH 5. One part of the goethite was equilibrated with organic substances before P[O.sub.4] addition, another part after addition of P[O.sub.4]. Before the desorption experiments, the porosity of our samples was analyzed by [N.sub.2] gas adsorption. In each treatment a rapid initial desorption was followed by a slow desorption reaction, which is assigned to the diffusion of P[O.sub.4] out of mineral pores. No consistent relation between the micro- and mesoporosity and the rate of the slow P[O.sub.4] desorption was observed. Compared with the C-free control, only PGA and MU affected the fraction of P[O.sub.4] mobilized by the fast and slow desorption reaction: when PGA was sorbed to goethite before P[O.sub.4], twice as much P[O.sub.4] was mobilized via the fast reaction than in the treatment where P[O.sub.4] was sorbed before PGA, suggesting a decreased accessibility of goethite pores to P[O.sub.4]. Mucigel, however, showed reversed effects, which is ascribed to its differing chemical composition. In conclusion, PGA seems inappropriate as a model substance for maize MU collected from non-axenic sand cultures. Under the experimental conditions chosen, the efficacy of all organic substances to increase P[O.sub.4] solution concentrations by pore clogging and sorption competition is small.
    Keywords: Phosphates -- Research ; Sorption -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 8
    Language: English
    In: Soil Science Society of America Journal, March-April, 2006, Vol.70(2), p.541(9)
    Description: Biogenetic polysugars may affect the sorption characteristics of soil mineral particles in the rhizosphere. We hypothesized that polygalacturonate [PGA, ([[C.sub.6][H.sub.7][O.sub.6]).sub.n.sup.-]] coatings on goethite reduce the diffusion of phosphate into the pores of the adsorbent. Goethite was preloaded with PGA (0-10 mg C [g.sup.-1]). The samples were characterized by [N.sub.2] and C[O.sub.2] adsorption, electrophoretic mobility measurements, and scanning electron microscopy/energy dispersive X-ray analysis (SEM-EDX). The phosphate sorption kinetics was studied with batch experiments over 2 wk at pH 5 and an initial phosphate concentration of 250 [micro]M. Pore volume and specific surface area of the goethite samples declined after PGA addition. The PGA coatings reduced the [zeta]-potential of goethite from 42.3 to -39.6 mV at the highest C loading. With increasing PGA-C content and decreasing [zeta]-potential the amount of phosphate sorbed after 2 wk decreased linearly (P 〈 0.001). Sorption of phosphate to pure and PGA-coated goethite showed an initial fast sorption followed by a slow sorption reaction. At the smallest C loading (5.5 mg C [g.sup.-1]) the portion of phosphate retained by the slow reaction was smaller than for the treatment without any PGA, while at higher C loadings the fraction of slowly immobilized phosphate increased. Our results suggest that at low C-loadings PGA impaired the intraparticle diffusion of phosphate. In contrast, the slow step-by-step desorption of PGA (〈52% within 2 wk) or the diffusion of phosphate through PGA coatings or both are rate limiting for the slow phosphate reaction at C loadings 〉 5.5 mg C [g.sup.-1].
    Keywords: Soil Phosphorus -- Research ; Soil Chemistry -- Research ; X-ray Analysis
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Soil Science Society of America Journal, Sept-Oct, 2006, Vol.70(5), p.1547(9)
    Description: Organic coatings on Fe oxides can decrease the accessibility of intraparticle pores for oxyanions like phosphate. We hypothesized that the slow sorption of phosphate to goethite coated with polygalacturonate (PGA) is controlled by the accessibility of external goethite surfaces to phosphate rather than by diffusion of phosphate into micropores ([empty set] 〈 2 nm). We studied the phosphate sorption kinetics of pure and PGA-coated goethites that differed in their microporosity ([N.sub.2] at 77 K, 46 vs. 31 [mm.sup.3] [g.sup.-1]). Because drying may affect the structure or surface coverage of PGA, we also tested the effect of freeze-drying on the slow phosphate sorption. The samples were examined by gas adsorption ([N.sub.2], C[O.sub.2]) and electrophoretic mobility measurements. Phosphate sorption and PGA-C desorption were studied in batch experiments for 3 wk at pH 5. In PGA-coated samples, the slow phosphate sorption was independent of micropore volume. Phosphate displaced on average 57% of PGA-C within 3 wk. Similar to phosphate sorption, the PGA-C desorption comprised a rapid initial desorption, which was followed by a slow C desorption. Sorption competition between phosphate and presorbed PGA depended on the 〈10-nm porosity and the C loading of the adsorbent. The efficacy of phosphate to desorb PGA generally increased after freeze-drying. We conclude for PGA-coated goethites that (i) freeze-drying biased the slow phosphate sorption by changing the structure/surface coverage of PGA, and (ii) within the time frame studied, micropores did not limit the rate of the slow phosphate sorption. Rather, the slow, gradual desorption of PGA and/or the diffusion of phosphate through PGA coatings controlled the slow phosphate sorption to PGA-coated goethite.
    Keywords: Mineralogical Research -- Analysis ; Phosphates -- Research ; Sorption -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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