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  • Knicker, Heike  (33)
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  • 1
    Language: English
    In: Geoderma, 2011, Vol.162(1), pp.96-106
    Description: Xe nuclear magnetic resonance (NMR) spectroscopic studies of xenon gas adsorbed on model systems representing soil porous components (Al (hyrd)oxides and charcoals) as well as natural soil materials (derived from a non-allophanic Andosol) were performed with the aim of characterising their micro- (〈 2 nm) and mesopores (2–50 nm). Both conventional, i.e. thermally polarised (TP), and laser-polarised or hyperpolarised (HP) Xe NMR was applied. The latter technique significantly increased sensitivity of the measurements. Information on the pore size range was derived from the Xe resonance shifts, , monitored as function of Xe loading, whereas the temperature dependences of provided information on the nature of xenon–pore surface interactions in terms of effective adsorption enthalpies. Dissolved organic matter (DOM) sorption on the mesoporous Al O was shown to proceed inhomogeneously indicative by the Xe adsorption enthalpies corresponding to the co-existing “empty” pores and pores coated with organic species. In AlOOH, an interconnected system of micro- and mesopores was tested. The enhanced sensitivity of HP Xe NMR allowed us detecting micropores in charcoals, where N adsorption method underestimated porosity due to the restricted N diffusion at 77 K. The interconnected pore structure of charcoals was attributed to the voids formed by both polyaromatic and aliphatic domains (evidenced by C NMR). The observed differences between the TP- and HP Xe NMR patterns were explained by the restricted xenon diffusion through charcoal particles caused by the constricted pore openings. Their suggested size is of the order of one or two diameters of the Xe atom. For the Andosol clay fractions, the large low-field Xe shifts (up to 175 ppm) increasing with Xe pressure indicated a developed porosity most obviously comprised by the interconnected micro- and mesopores. Such porous network may originate from the “multi-domain” structure of soil clay particles, i.e. particles formed by agglomerated nano-sized crystallites. The latter are assumed to be the polynuclear Al (H O) (OH) clusters formed by hydrolysis reactions of Al species after the destroying of Al-humus complexes by the H O -oxidation. ► Xe NMR spectroscopy shows perspectives in studying soil porous components. ► Inhomogeneous DOM sorption in mesopores followed from the Xe adsorption enthalpies. ► Constricted pore openings within the microporous network of charcoals were revealed. ► Enhanced porosity of non-allophanic Andosol is due to the “multi-domain” particle structure. ► Hyperpolarised Xe NMR is helpful for assessing the extent of pore attainability.
    Keywords: Xenon ; Nuclear Magnetic Resonance ; Meso- and Micropores ; Adsorption ; Charcoals ; Andosol ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 2
    Language: English
    In: Environmental science & technology, 15 January 2011, Vol.45(2), pp.527-33
    Description: In soil and water, ferrihydrite frequently forms in the presence of dissolved organic matter. This disturbs crystal growth and gives rise to coprecipitation of ferrihydrite and organic matter. To compare the chemical fractionation of organic matter during coprecipitation with the fractionation involved in adsorption onto pristine ferrihydrite surfaces we prepared ferrihydrite-organic matter associations by adsorption and coprecipitation using (i) a forest-floor extract or (ii) a sulfonated lignin. The reaction products were studied by (13)C CPMAS NMR, FTIR, and analysis of hydrolyzable neutral polysaccharides. Relative to the original forest-floor extract, the ferrihydrite-associated organic matter was enriched in polysaccharides, especially when adsorption took place. Moreover, mannose and glucose were bound preferentially to ferrihydrite, while fucose, arabinose, xylose, and galactose accumulated in the supernatant. This fractionation of sugar monomers was more pronounced during coprecipitation and led to an enhanced ratio of (galactose + mannose)/(arabinose + xylose). Experiments with lignin revealed that the ferrihydrite-associated material was enriched in its aromatic components but had a lower ratio of phenolic C to aromatic C than the original lignin. A compositional difference between the adsorbed and coprecipitated lignin is obvious from a higher contribution of methoxy C in the coprecipitated material. Coprecipitated organic matter may thus differ in amount and composition from adsorbed organic matter.
    Keywords: Chemical Fractionation ; Chemical Precipitation ; Ferric Compounds -- Chemistry ; Organic Chemicals -- Chemistry ; Soil Pollutants -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 3
    Language: English
    In: Phytochemistry, 2003, Vol.62(7), pp.1159-1170
    Description: MALDI-TOF mass spectrometry and 13 C NMR spectroscopy were applied to unveil typical characteristics of condensed tannins of leaves and needles from willow ( Salix alba ), spruce ( Picea abies ) and beech ( Fagus sylvatica ) of three tree species that are ubiquitous in German forests and landscapes. For further evaluation, lime ( Tilia cordata ) was included. The 13 C NMR spectroscopy confirmed the purity of the condensed tannin fractions and the efficiency of the procedure used for their extraction. While signals representative for procyanidin units are observable in all liquid-state 13 C NMR spectra, resonance lines of prodelphinidin were only detected in those obtained from the condensed tannins of spruce needles and beech leaves. Typical signals in the chemical shift region between 70 and 90 ppm demonstrated the presence of stereoisomers (catechin/epicatechin; gallocatechin/ epigallocatechin). The MALDI-TOF mass spectra of the condensed tannins show signals of polymers of up to undecamers. Supporting the observations from the NMR spectroscopy, the mass spectra of the willow and lime leaf condensed tannins were identified as polymers with mainly procyanidin units, while the polymers of the spruce needle and beech leaves exhibit varying procyanidin/prodelphinidin ratios. Post source decay (PSD) fragmentation lead to a sequential loss of monomers and allowed a detailed characterization and sequencing of individual chains. In the case of the condensed tannins of lime this technique clearly excludes a pelargonidin terminal unit followed by a prodelphinidin unit, which would result in the same molecular masses as a polymer solely built up of procyanidin units. Within this work, MALDI-TOF mass spectrometry, PDS fragmentation and 13 C NMR spectroscopy was applied for the determination of the chain length and chemical composition of condensed tannins isolated from leaves and needles of ubiquitous trees.
    Keywords: Salix Alba ; Picea Abies ; Fagus Sylvatica ; Tilia Cordata ; Condensed Tannins ; Maldi-Tof ; Psd Fragmentation ; NMR ; Procyanidin ; Prodelphinidin ; Pelargonidin ; Botany
    ISSN: 0031-9422
    E-ISSN: 1873-3700
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, 2003, Vol.35(4), pp.577-589
    Description: Alterations of the chemical structure of condensed tannins (CT) during decomposition of Norway spruce (Picea abies) needles and white willow (Salix alba) leaves were investigated by gel permeation chromatography (GPC), super(13)C nuclear magnetic resonance (NMR) spectroscopy, and matrix- assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS). The effect of these alterations on their protein binding capacity was determined by radial diffusion assay on an agarose plate. For these studies an incubation experiment was performed with spruce needles and willow leaves. From the fresh foliage and its decomposed materials obtained after 4- days, and 1-, 2-, 4-, and 8-weeks of incubation, CT were extracted and analyzed. Dynamics of CT alterations during decomposition of the fresh foliage were different for the two plant species, although the amount of extractable CT for both decreased soon after incubation and only slight amounts of CT were extractable after 8 weeks of incubation. The decrease was faster for the willow leaves than for the spruce needles. Solution super(13)C NMR revealed alterations of CT isolated from both degrading plant materials, but only to a small extent. However, considerable changes in chemical composition and chain length of the CT were detected by MALDI-TOF MS. Changes in the chemical composition of CT are expected to decrease the protein binding capacity. Applying the radial diffusion assay, this assumption was confirmed for spruce CT, but not for willow CT. This may be explained by (1) higher reactivity of prodelphinidin (PD) than procyanidin (PC), the former is contained in spruce CT but not in willow CT and (2) the slower decomposition rate of spruce needles than willow leaves. Thus, CT in spruce needles may have suffered a greater extent of chemical alteration, which formed partially altered CT with less protein binding capacity. Further, since the decomposition rate of spruce needles was slower than that of willow leaves, the partially altered CT remained extractable for a longer incubation period compared with the willow leave's CT.
    Keywords: 13c NMR Spectroscopy ; Condensed Tannins ; Decomposition ; Maldi-Tof MS ; Proanthocyanidin ; Protein Binding Capacity ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Soil Biology and Biochemistry, 2000, Vol.32(2), pp.241-252
    Description: The structure of nitrogen-containing compounds of the fine particle size fractions (〈20 μm) of two Podzols obtained from the highly industrialized Ruhr area in Germany, were examined by means of solid-state 15 N nuclear magnetic resonance (NMR) spectroscopy. In order to improve the signal-to-noise ratio of the spectra, the samples were treated with hydrofluoric acid (HF), prior to NMR analysis. Comparing the solid-state 15 N NMR spectra of plant incubates obtained before and after HF treatment revealed no major alteration of the nitrogen fraction induced by HF. From 60 to 90% of the nitrogen detectable in the solid-state 15 N NMR spectra of the soil particle size fractions were assigned to amides. A smaller signal derives from free amino groups, leading to the conclusion that most of the nitrogen was derived from peptide-like structures. The calculated high contribution of peptides to the total organic carbon and nitrogen of the samples confirms earlier studies demonstrating that peptide-like material plays a more important role in refractory soil organic matter formation than commonly thought. Major contributions of N-containing heterocyclic aromatic compounds, formed by recondensation reactions or deriving from the input of coal and soot particles from coal processing industries, were not identified. Obviously, in these fractions, contamination did not significantly alter the chemical composition of the organic nitrogen.
    Keywords: Solid-State 13c and 15n NMR Spectroscopy ; Particle Size Separates ; Soil Organic Matter ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 6
    Language: English
    In: Plant and Soil, 2005, Vol.268(1), pp.319-328
    Description: The long-term soil management effects on C and N stocks of soil physical fractions are still poorly understood for South American subtropical soils. This study aimed (i) to evaluate the influence of cereal- and legume-based cropping systems and N fertilisation on C and N stocks of the sand-, silt- and clay-size fractions of a no-tilled subtropical Acrisol in southern Brazil, (ii) to compute the Carbon Management Index (CMI) for those cropping systems using physical fractionation data, and (iii) to investigate the possible existence of finite capacity of those soil physical fractions to store C and N. Soil samples of a long-term experiment were collected from the 0–2.5 and 2.5–7.5 cm layers of three no-till cropping systems [fallow bare soil, oat/maize (O/M) and pigeon pea+maize (P+M)] under two N fertilisation levels (0 and 180 kg N ha −1 ). However, for fallow bare soil, only the non-fertilised sub-plot was sampled. An adjacent native grassland soil was sampled as a reference. The C and N stocks of the three soil physical fractions were higher in the legume-based cropping system (P+M) than in O/M and bare soil, because of the higher residue input in the former. The P+M cropping system restored the C and N stocks in sand- and silt-size fractions to the same levels found in grassland soil. Higher C and N stocks in all physical fractions were also obtained with N fertilisation. The C and N stocks and the C:N ratio were most affected by cropping systems in the sand- and least in the clay-size fraction. Particulate organic matter was found in the silt-size fraction, showing this fraction is not only constituted by mineral-associated organic mater, as commonly believed. Taking grassland soil as reference (CMI = 100), the CMI ranged from 46, in O/M no N, to 517, in P+M with N, pointing to a better soil management in the latter. The clay-size fraction tended to show a finite capacity to store C and N (48.8 g C kg −1 and 4.9 g N kg −1 of clay), which was not verified in sand- and silt-size fractions. The adoption of no-tillage and legume-based cropping systems with high residue input are adequate soil management strategies to improve soil quality and make the agricultural production systems more sustainable in subtropical regions.
    Keywords: carbon saturation ; Carbon Management Index ; leguminous ; no-tillage ; particle-size fractions ; subtropical soils
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    Language: English
    In: Soil Biology and Biochemistry, 2009, Vol.41(8), pp.1622-1631
    Description: Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitrifiers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined. Surprisingly plants preferred organic N over inorganic N and nitrate (NO ) over ammonium (NH ) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms.
    Keywords: N Mineralization ; Nitrification ; Denitrification ; Microbial Immobilization ; Plant N Uptake ; Amino Acid ; Beech ; Competition ; N Metabolite Profiling ; Mycorrhiza ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 8
    Language: English
    In: Organic Geochemistry, 2000, Vol.31(7), pp.609-625
    Description: Structural information on soil organic matter (SOM) at the molecular level can be obtained on diverse structural units that are amenable to degradation techniques. Chemolytic techniques in combination with colorimetric analyses or GC MS are used to determine amino acids (proteins), sugars (polysaccharides), lipids, or aromatic oxidation products from lignin or charred organic matter. Microbial markers (amino sugars, muramic acid) are analyzed after hydrolysis and gas chromatographic separation. Macromolecular structures can also be subjected to thermochemolytic degradation or pyrolysis and subsequent analysis of the fragments by GC MS. Alternative techniques for the examination of organic matter in heterogeneous macromolecular mixtures are non-destructive spectroscopic methods, such as nuclear magnetic resonance (NMR) spectroscopy. Although this technique can give good results concerning the gross chemical composition, specific compounds are hardly identified. The combination of spectroscopic techniques with thermolytic and chemolytic methods will add substantially to the understanding of the nature of refractory soil organic matter. Physical fractionation prior to analysis provides a means to differentiate between distinct SOM pools that can be further characterized by the methods described above. Studies on SOM structural characteristics have focused mainly on the A horizons of soils under agriculture and litter biodegradation in forest soils and need to be extended to a wider variety of soil types and the subsoil.
    Keywords: Soil Organic Matter ; Pyrolysis ; 13c NMR Spectroscopy ; 15n NMR Spectroscopy ; Chemolysis ; Tmah ; Humic Substances ; Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 9
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2004, Vol.167(5), pp.545-555
    Description: Relationships between soil lightness, soil organic matter (SOM) composition, content of organic C, CaCO, and texture were studied using 42 top‐soil horizons from different soil types located in southern Germany. SOM composition was determined by CPMAS C NMR spectroscopy, soil color was measured by diffuse‐reflectance spectrophotometry and given in the CIE L*a*b* color coordination system (, 1978). Multiple‐regression analysis showed, that soil lightness of top‐soil horizons is principally determined by OC concentration, but CaCO and soil texture are also major variables. Soil lightness decreased with increasing OC content. Carbonate content had an important effect on soil lightness even at low concentrations due to its lightening property. Regressions between soil lightness and organic C content were strongly linear, when the soils were differentiated according to texture and CaCO content. The aryl‐C content was the only SOM component which correlated significantly with soil lightness (r = –0.87). In the linear regressions carried out on the different soil groups, soil aryl‐C content was a more significant predictor for soil lightness than total OC content. Zusammensetzung der organischen Bodensubstanz und Bodenhelligkeit Der Zusammenhang zwischen Bodenhelligkeit, Zusammensetzung der organischen Substanz und Gehalt an C, CaCO und Textur wurde in 42 Oberböden aus verschiedenen Bodentypen Süddeutschlands untersucht. Die Zusammensetzung der organischen Substanz wurde mittels CPMAS‐C‐NMR‐Spektroskopie bestimmt, die Bodenfarbe mittels Spektralphotometer und als Bodenhelligkeitswert im CIE L*a*b*‐Farbkoordinatensystem (, 1978) angegeben. Die Auswertung über multiple Regression zeigte, dass die Bodenhelligkeit hauptsächlich vom OC‐Gehalt bestimmt wird; CaCO‐Gehalt und Textur erwiesen sich als weitere relevante Variablen. Die Bodenhelligkeit nimmt mit zunehmendem OC‐Gehalt ab. Aufgrund seiner stark aufhellenden Wirkung hat der Carbonatgehalt auch bei niedrigen Konzentrationen einen deutlichen Einfluss auf die Bodenhelligkeit. Bei Berücksichtigung der Textur und des Carbonatgehalts ergaben sich lineare Beziehungen zwischen Bodenhelligkeit und OC‐Gehalt. Der Aryl‐C‐Gehalt des Bodens war als einzige Humuskomponente signifikant mit der Bodenhelligkeit korreliert (r = –0.87). Der Aryl‐C‐Gehalt des Bodens bestimmt die Bodenhelligkeit schärfer als der OC‐Gehalt.
    Keywords: Soil Color ; Aromatic Carbon ; Soil Organic Matter ; Solid‐State C Nmr Spectroscopy ; Caco
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 10
    Language: English
    In: Organic Geochemistry, December 2002, Vol.33(12), pp.1715-1726
    Description: N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS (super 13) C and (super 15) N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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