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Berlin Brandenburg

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  • 1
    Language: English
    In: Soil Biology and Biochemistry, February 2017, Vol.105, pp.A3-A8
    Description: My 2002 SBB paper, , brought together knowledge on the chemical composition of the diverse inputs to soil organic matter. Both plant and microbial residues were examined with the analysis of their composition using a combination of different techniques. From this, the limitations of conventional proximate analysis methods were identified and the great potential of recent techniques, in particular solid-state C NMR spectroscopy and molecular level analysis, for the overall characterization of the input materials were discussed. The paper emphasised the importance of differentiating between organic matter from plants (above-ground litter, root litter and rhizodeposition), microbial residues and extracellular polymers and their breakdown products as well as the need for quantitative measurements of the amounts of these materials entering soils. In the last 14 years much new knowledge has been generated regarding these inputs and their alteration during decomposition, yet we still lack quantitative data for the amounts, composition and transformations of the many different forms of organic matter entering the soil. This is particularly the case regarding the inputs to the subsoil root litter and rhizodeposition and the significance of microbial residues and extracellular polymers and their turnover.
    Keywords: Litter ; Microbial Residues ; Subsoil ; NMR Spectroscopy ; Rhizosphere ; Root Litter ; OM Turnover ; Molecular Composition ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 2
    Language: English
    In: Plant and Soil, 2011, Vol.338(1), pp.143-158
    Description: Despite their low carbon (C) content, most subsoil horizons contribute to more than half of the total soil C stocks, and therefore need to be considered in the global C cycle. Until recently, the properties and dynamics of C in deep soils was largely ignored. The aim of this review is to synthesize literature concerning the sources, composition, mechanisms of stabilisation and destabilization of soil organic matter (SOM) stored in subsoil horizons. Organic C input into subsoils occurs in dissolved form (DOC) following preferential flow pathways, as aboveground or root litter and exudates along root channels and/or through bioturbation. The relative importance of these inputs for subsoil C distribution and dynamics still needs to be evaluated. Generally, C in deep soil horizons is characterized by high mean residence times of up to several thousand years. With few exceptions, the carbon-to-nitrogen (C/N) ratio is decreasing with soil depth, while the stable C and N isotope ratios of SOM are increasing, indicating that organic matter (OM) in deep soil horizons is highly processed. Several studies suggest that SOM in subsoils is enriched in microbial-derived C compounds and depleted in energy-rich plant material compared to topsoil SOM. However, the chemical composition of SOM in subsoils is soil-type specific and greatly influenced by pedological processes. Interaction with the mineral phase, in particular amorphous iron (Fe) and aluminum (Al) oxides was reported to be the main stabilization mechanism in acid and near neutral soils. In addition, occlusion within soil aggregates has been identified to account for a great proportion of SOM preserved in subsoils. Laboratory studies have shown that the decomposition of subsoil C with high residence times could be stimulated by addition of labile C. Other mechanisms leading to destabilisation of SOM in subsoils include disruption of the physical structure and nutrient supply to soil microorganisms. One of the most important factors leading to protection of SOM in subsoils may be the spatial separation of SOM, microorganisms and extracellular enzyme activity possibly related to the heterogeneity of C input. As a result of the different processes, stabilized SOM in subsoils is horizontally stratified. In order to better understand deep SOM dynamics and to include them into soil C models, quantitative information about C fluxes resulting from C input, stabilization and destabilization processes at the field scale are necessary.
    Keywords: Subsoil ; Organic matter ; Chemical composition ; Carbon stabilization
    ISSN: 0032-079X
    E-ISSN: 1573-5036
    Source: Springer Science & Business Media B.V.
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  • 3
    Language: English
    In: Science of the Total Environment, 01 December 2015, Vol.536, pp.1045-1051
    Description: To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1016/j.scitotenv.2015.07.064 Byline: Martin Wiesmeier [wiesmeier@wzw.tum.de] (a,*), Rico Hubner (b), Ingrid Kogel-Knabner (a,c) Keywords Soil organic carbon; Climate change; Net primary productivity; Soil C input Highlights * C stocks in agricultural soils may be largely affected by climate change. * It is assumed that C stocks would increase due to an assumed increase of NPP. * However, crop statistics indicate stagnating yields of major crops since the 1990s. * Concurrently stagnating C inputs would lead to C decreases in the long-term. * Indications for declining agricultural C stocks were already found. Abstract The carbon (C) balance of agricultural soils may be largely affected by climate change. Increasing temperatures are discussed to cause a loss of soil organic carbon (SOC) due to enhanced decomposition of soil organic matter, which has a high intrinsic temperature sensitivity. On the other hand, several modeling studies assumed that potential SOC losses would be compensated or even outperformed by an increased C input by crop residues into agricultural soils. This assumption was based on a predicted general increase of net primary productivity (NPP) as a result of the CO.sub.2 fertilization effect and prolonged growing seasons. However, it is questionable if the crop C input into agricultural soils can be derived from NPP predictions of vegetation models. The C input in European croplands is largely controlled by the agricultural management and was strongly related to the development of crop yields in the last decades. Thus, a glance at past yield development will probably be more instructive for future estimations of the C input than previous modeling approaches based on NPP predictions. An analysis of European yield statistics indicated that yields of wheat, barley and maize are stagnating in Central and Northern Europe since the 1990s. The stagnation of crop yields can probably be related to a fundamental change of the agricultural management and to climate change effects. It is assumed that the soil C input is concurrently stagnating which would necessarily lead to a decrease of agricultural SOC stocks in the long-term given a constant temperature increase. Remarkably, for almost all European countries that are faced with yield stagnation indications for agricultural SOC decreases were already found. Potentially adverse effects of yield stagnation on the C balance of croplands call for an interdisciplinary investigation of its causes and a comprehensive monitoring of SOC stocks in agricultural soils of Europe. Author Affiliation: (a) Lehrstuhl fur Bodenkunde, Department fur Okologie und Okosystemmanagement, Wissenschaftszentrum Weihenstephan fur Ernahrung, Landnutzung und Umwelt, Technische Universitat Munchen, 85350 Freising-Weihenstephan, Germany (b) Lehrstuhl fur Strategie und Management der Landschaftsentwicklung, Department fur Okologie und Okosystemmanagement, Wissenschaftszentrum Weihenstephan fur Ernahrung, Landnutzung und Umwelt, Technische Universitat Munchen, 85350 Freising-Weihenstephan, Germany (c) Institute for Advanced Study, Technische Universitat Munchen, Lichtenbergstr. 2a, 85748 Garching, Germany * Corresponding author. Article History: Received 23 April 2015; Revised 12 July 2015; Accepted 13 July 2015 (miscellaneous) Editor: D. Barcelo
    Keywords: Soil Organic Carbon ; Climate Change ; Net Primary Productivity ; Soil C Input ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, December 2013, Vol.67, pp.235-244
    Description: Interactions between organic matter (OM), minerals and charcoal may play an important role in the development and stabilization of OM in soils. However, these interactions are difficult to characterize in natural soils, which are usually very complex systems with unknown initial conditions. We developed so-called ‘artificial soils’ with a texture and OM content similar to natural arable soils that were incubated up to 18 months. The aim was to determine the turnover and development of OM with incubation time, and to establish the effect of mineral composition and charcoal presence on organic carbon (OC) and N distribution and properties. Artificial soils were composed of quartz, manure as OM source and a microbial community extracted from a natural arable soil, with 8 different mixtures of montmorillonite, illite, ferrihydrite, boehmite and charcoal. We determined C and N particle size distribution with time and used solid-state C nuclear magnetic resonance (NMR) spectroscopy and acid hydrolysis to determine the development of OM composition. The CO respiration rate and distribution of OC and N with particle size was similar for all artificial soil compositions. OC and N accumulated in the 〈20 μm fraction over time and approximately 50% of coarse (〉200 μm) particulate OM was lost after 18 months of incubation. C NMR spectroscopy indicated accumulation of protein-rich OC in the 〈20 μm fraction, likely in the form of microbially produced substances. Acid hydrolysis showed a higher content of non-hydrolysable N in the mixtures containing clay minerals, indicating that some of the nitrogen present was strongly bound to phylosilicate surfaces. Ferrihydrite did not have any effect on non-hydrolysable N. From this, it can be concluded that in the artificial soils, clay minerals were more important than metal-oxides for the binding of nitrogen and OC. Overall, the artificial soils developed similarly to incubation experiments with natural soils, and were therefore a valuable model system where the effect of specific components on the development and turnover of soil OM could be determined under simplified conditions.
    Keywords: Clay Mineral ; Ferrihydrite ; Charcoal ; Acid Hydrolysis ; Organic Nitrogen ; Artificial Soil ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Soil biology & biochemistry, 2013, Vol.67, pp.235-244
    Description: Interactions between organic matter (OM), minerals and charcoal may play an important role in the development and stabilization of OM in soils. However, these interactions are difficult to characterize in natural soils, which are usually very complex systems with unknown initial conditions. We developed so-called ‘artificial soils’ with a texture and OM content similar to natural arable soils that were incubated up to 18 months. The aim was to determine the turnover and development of OM with incubation time, and to establish the effect of mineral composition and charcoal presence on organic carbon (OC) and N distribution and properties. Artificial soils were composed of quartz, manure as OM source and a microbial community extracted from a natural arable soil, with 8 different mixtures of montmorillonite, illite, ferrihydrite, boehmite and charcoal. We determined C and N particle size distribution with time and used solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy and acid hydrolysis to determine the development of OM composition. The CO₂ respiration rate and distribution of OC and N with particle size was similar for all artificial soil compositions. OC and N accumulated in the 200 μm) particulate OM was lost after 18 months of incubation. ¹³C NMR spectroscopy indicated accumulation of protein-rich OC in the 〈20 μm fraction, likely in the form of microbially produced substances. Acid hydrolysis showed a higher content of non-hydrolysable N in the mixtures containing clay minerals, indicating that some of the nitrogen present was strongly bound to phylosilicate surfaces. Ferrihydrite did not have any effect on non-hydrolysable N. From this, it can be concluded that in the artificial soils, clay minerals were more important than metal-oxides for the binding of nitrogen and OC. Overall, the artificial soils developed similarly to incubation experiments with natural soils, and were therefore a valuable model system where the effect of specific components on the development and turnover of soil OM could be determined under simplified conditions. ; p. 235-244.
    Keywords: Particle Size ; Charcoal ; Texture ; Illite ; Organic Matter ; Ferrihydrite ; Carbon Dioxide ; Mineral Content ; Nitrogen ; Acid Hydrolysis ; Microbial Communities ; Carbon ; Quartz ; Respiratory Rate ; Arable Soils ; Particle Size Distribution ; Nuclear Magnetic Resonance Spectroscopy ; Montmorillonite
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 6
    Language: English
    In: Geochimica et Cosmochimica Acta, 01 May 2016, Vol.180, pp.284-302
    Description: We evaluated the impact of nano-structural characteristics of allophanic compounds and Fe oxide speciation on the efficiency of organo-mineral interactions in an allophanic derived from volcanic ash (Eifel mountains, Germany). The samples selected for our work represented a gradient from: (i) a pure synthetic allophane and (ii) model organo-mineral mixtures to (iii) particle size fractions of the natural Andosol. We thus aimed to link the processes operating at the individual molecular scale to the phenomena active at the aggregate scale. For a non-destructive characterization of the samples, we applied Xe NMR spectroscopy of adsorbed Xe atoms (to identify the mineral nano-structure and surface acid centres), ESEM (verifying the nano-spherical structure of allophane), C CPMAS NMR (for the nature of the soil organic matter (SOM)), Fe Mössbauer spectroscopy (Fe oxide speciation), and N adsorption (contribution of micro- and mesoporosity). By using the atomic probe Xe, we obtained evidence for a mechanism of adsorption onto allophane requiring both the narrow pores (voids formed by the primary nano-spherules) and the acid centres located at the defect surfaces of the primary spherules. The validity of this coupled mechanism for the sorption of organic matter was confirmed by the concomitant blocking of acid centres ( Xe NMR data) and the decrease of the N -available pore volumes ( and ) in the model samples DOM/- and NOM/allophane (DOM = dissolved OM, NOM = natural OM). In the Andosol, the high resistance of SOM against oxidation (OC = 15–50%) was combined with preferential accumulation of certain organic compounds, e.g. potentially labile substrates such as carbohydrates, and the low molecular weight species such as amino acids. This feature was attributed to the peculiar microporous tortuous structure of allophane aggregates that likely impose certain criteria for the chemical nature and size of mineral-bound SOM. On the other hand, the revealed dominance of nanoparticulate Fe oxyhydroxides (57% ferrihydrite) and Fe-substituted allophane (supposedly formed due to co-precipitation of the Al, Si and Fe in the course of volcanic soil formation) may substantially contribute to the formation of highly resistant organo-mineral associations through the enhanced extent of reactive surface groups in nanoparticles, increased surface charge density and electron accepting properties of substituting Fe species that supposedly enhance the proportion of oxidised organic components.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 7
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 May 2012, Vol.85, pp.1-18
    Description: Interactions between organic and mineral constituents prolong the residence time of organic matter in soils. However, the structural organization and mechanisms of organic coverage on mineral surfaces as well as their development with time are still unclear. We used clay fractions from a soil chronosequence (15, 75 and 120 years) in the foreland of the retreating Damma glacier (Switzerland) and from mature soils outside the proglacial area (〉700 and 〈3000 years) to elucidate the evolution of organo–mineral associations during initial soil formation. The chemical composition of the clay-bound organic matter (OM) was assessed by solid-state C NMR spectroscopy while the quantities of amino acids and neutral sugar monomers were determined after acid hydrolysis. The mineral phase was characterized by X-ray diffraction, oxalate extraction, specific surface area by N adsorption (BET approach), and cation exchange capacity at pH 7 (CEC ). The last two methods were applied before and after H O treatment. We found pronounced shifts in quantity and quality of OM during aging of the clay fractions, especially within the first one hundred years of soil formation. The strongly increasing organic carbon (OC) loading of clay-sized particles resulted in decreasing specific surface areas (SSA) of the mineral phases and increasing CEC . Thus, OC accumulation was faster than the supply of mineral surfaces and cation exchange capacity was mainly determined by the OC content. Clay-bound OC of the 15-year-old soils showed high proportions of carboxyl C and aromatic C. This may point to remnants of ancient OC which were inherited from the recently exposed glacial till. With increasing age (75 and 120 years), the relative proportions of carboxyl and aromatic C decreased. This was associated with increasing O-alkyl C proportions, whereas accumulation of alkyl C was mainly detected in clay fractions from the mature soils. These findings from solid-state C NMR spectroscopy are in line with the increasing amounts of microbial-derived carbohydrates with soil age. The large accumulation of proteins, which was comparable to those of carbohydrates, and the very low C/N ratios of H O -resistant OM indicated strong and preferential associations between proteinaceous compounds and mineral surfaces. In the acid soils, poorly crystalline Fe oxides were the main providers of mineral surface area and important for the stabilization of OM during aging of the clay fractions. This was indicated by (I) the strong correlations between oxalate soluble Fe and both, SSA of H O -treated clay fractions and OC content, and (II) the low formation of expandable clays due to small extents of mineral weathering. Our chronosequence approach provided new insights into the evolution of organo–mineral interactions in acid soils. The formation of organo–mineral associations started with the sorption of proteinaceous compounds and microbial-derived carbohydrates on mineral surfaces which were mainly provided by ferrihydrite. The sequential accumulation of different organic compounds and the large OC loadings point to multiple accretion of OM in distinct zones or layers during the initial evolution of clay fractions.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 8
    Language: English
    In: Geochimica et cosmochimica acta, 2012, Vol.85, pp.1-18
    Description: Interactions between organic and mineral constituents prolong the residence time of organic matter in soils. However, the structural organization and mechanisms of organic coverage on mineral surfaces as well as their development with time are still unclear. We used clay fractions from a soil chronosequence (15, 75 and 120years) in the foreland of the retreating Damma glacier (Switzerland) and from mature soils outside the proglacial area (〉700 and 〈3000years) to elucidate the evolution of organo–mineral associations during initial soil formation. The chemical composition of the clay-bound organic matter (OM) was assessed by solid-state ¹³C NMR spectroscopy while the quantities of amino acids and neutral sugar monomers were determined after acid hydrolysis. The mineral phase was characterized by X-ray diffraction, oxalate extraction, specific surface area by N₂ adsorption (BET approach), and cation exchange capacity at pH 7 (CECₚH₇). The last two methods were applied before and after H₂O₂ treatment. We found pronounced shifts in quantity and quality of OM during aging of the clay fractions, especially within the first one hundred years of soil formation. The strongly increasing organic carbon (OC) loading of clay-sized particles resulted in decreasing specific surface areas (SSA) of the mineral phases and increasing CECₚH₇. Thus, OC accumulation was faster than the supply of mineral surfaces and cation exchange capacity was mainly determined by the OC content. Clay-bound OC of the 15-year-old soils showed high proportions of carboxyl C and aromatic C. This may point to remnants of ancient OC which were inherited from the recently exposed glacial till. With increasing age (75 and 120years), the relative proportions of carboxyl and aromatic C decreased. This was associated with increasing O-alkyl C proportions, whereas accumulation of alkyl C was mainly detected in clay fractions from the mature soils. These findings from solid-state ¹³C NMR spectroscopy are in line with the increasing amounts of microbial-derived carbohydrates with soil age. The large accumulation of proteins, which was comparable to those of carbohydrates, and the very low C/N ratios of H₂O₂-resistant OM indicated strong and preferential associations between proteinaceous compounds and mineral surfaces. In the acid soils, poorly crystalline Fe oxides were the main providers of mineral surface area and important for the stabilization of OM during aging of the clay fractions. This was indicated by (I) the strong correlations between oxalate soluble Fe and both, SSA of H₂O₂-treated clay fractions and OC content, and (II) the low formation of expandable clays due to small extents of mineral weathering. Our chronosequence approach provided new insights into the evolution of organo–mineral interactions in acid soils. The formation of organo–mineral associations started with the sorption of proteinaceous compounds and microbial-derived carbohydrates on mineral surfaces which were mainly provided by ferrihydrite. The sequential accumulation of different organic compounds and the large OC loadings point to multiple accretion of OM in distinct zones or layers during the initial evolution of clay fractions. ; p. 1-18.
    Keywords: Clay ; Glacial Till ; Iron Oxides ; Acid Soils ; Organic Matter ; Iron ; Nitrogen ; Sugars ; Carbon ; Amino Acids ; Chronosequences ; Soil Formation ; Age Of Soil ; Nuclear Magnetic Resonance Spectroscopy ; Ph ; Cation Exchange Capacity ; Glaciers ; Adsorption ; X-Ray Diffraction ; Ferrihydrite ; Weathering ; Organic Compounds ; Acid Hydrolysis ; Hydrogen Peroxide ; Proteins ; Surface Area
    ISSN: 0016-7037
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 9
    Language: English
    In: Soil biology & biochemistry, 2013, Vol.57, pp.1-13
    Description: ¹³C contents of organic matter are changing during decomposition of plant material and stabilization as soil organic carbon (SOC). In this context, several studies showed ¹³C enrichment in soil as compared to vegetation for C₃ forests, whereas depletion of ¹³C was frequently reported for C₄ grassland soil as compared to C₄ vegetation. These changes were often attributed to selective preservation and/or stabilization of specific organic compounds. This study investigates if changes in the chemical composition of OC and specifically lignin may explain the observed shifts in δ¹³C values from plant material to SOC. We analyzed aboveground biomass, roots and heavy organo-mineral fractions from topsoils in both, long-term stable C₄ grasslands and C₃ Araucaria forest situated nearby in the southern Brazilian highlands on soils with andic properties. The stable carbon isotope (¹²C/¹³C) composition was analyzed for total organic carbon (OCₜₒₜ) and lignin-derived phenols. The bulk chemical composition of OC was assessed by solid-state ¹³C NMR spectroscopy while neutral sugar monomers were determined after acid hydrolysis. The shifts of the ¹³C/¹²C isotope signature during decomposition and stabilization (plant tissues versus soil heavy fractions) showed similar trends for VSC phenols and OCₜₒₜ (¹³C depletion in C₄ grassland soil and ¹³C enrichment in C₃ forest soil compared to the corresponding vegetation). In this regard, the isotopic difference between roots and aboveground biomass was not relevant, but may become more important at greater soil depths. ¹³C depletion of VSC lignins relative to OCₜₒₜ was higher in C₃-biomass and C₃-derived SOC compared to the C₄ counterparts. As lignin contents of heavy fractions were low, in particular for those with C₄ isotopic signature, the influence of lignin on OCₜₒₜ δ¹³C values in grassland topsoils is presumably low. Rather, the presence of charred grass residues and the accumulation of alkyl C in heavy fractions as revealed by ¹³C NMR spectroscopy contribute to decreasing δ¹³C values from grass biomass to C₄-derived heavy fractions. In forest topsoils, the accumulation of ¹³C depleted VSC lignin residues in heavy fractions counteracts the prevailing ¹³C enrichment of OCₜₒₜ from plant biomass to heavy fractions. Nonetheless, non-lignin compounds with relatively high ¹³C contents like microbial-derived OC have a stronger influence on δ¹³C values of OCₜₒₜ in forest soils than lignins or aliphatic biopolymers. The mineral-associated SOC is in a late phase of decomposition with large contributions of microbial-derived carbohydrates, but distinct structural and isotopical alterations of lignin between C₄- and C₃-derived heavy fractions. This may indicate different processes and/or extent of lignin (and SOM) biodegradation between C₄ grassland and C₃ forest resulting from other kind of decomposer communities in association with distinct types and amounts of plant input as source of SOM and thus, carbon source for microbial transformation. Our results indicate that the importance of lignin for δ¹³C values of OCₜₒₜ was overestimated in previous studies, at least in subtropical C₄ grassland and C₃ forest topsoils. ; p. 1-13.
    Keywords: Soil Organic Carbon ; Forest Soils ; Forests ; Biodegradation ; Lignin ; Roots ; Organic Matter ; Highlands ; Stable Isotopes ; Sugars ; Grasses ; Soil Depth ; Phenols ; Soil Texture ; Acid Hydrolysis ; Carbon ; Grasslands ; Grassland Soils ; Araucaria ; Plant Tissues ; Aboveground Biomass ; Biopolymers ; Nuclear Magnetic Resonance Spectroscopy
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 10
    Language: English
    In: Soil Biology and Biochemistry, February 2013, Vol.57, pp.1-13
    Description: C contents of organic matter are changing during decomposition of plant material and stabilization as soil organic carbon (SOC). In this context, several studies showed C enrichment in soil as compared to vegetation for C forests, whereas depletion of C was frequently reported for C grassland soil as compared to C vegetation. These changes were often attributed to selective preservation and/or stabilization of specific organic compounds. This study investigates if changes in the chemical composition of OC and specifically lignin may explain the observed shifts in δ C values from plant material to SOC. We analyzed aboveground biomass, roots and heavy organo-mineral fractions from topsoils in both, long-term stable C grasslands and C Araucaria forest situated nearby in the southern Brazilian highlands on soils with andic properties. The stable carbon isotope ( C/ C) composition was analyzed for total organic carbon (OC ) and lignin-derived phenols. The bulk chemical composition of OC was assessed by solid-state C NMR spectroscopy while neutral sugar monomers were determined after acid hydrolysis. The shifts of the C/ C isotope signature during decomposition and stabilization (plant tissues versus soil heavy fractions) showed similar trends for VSC phenols and OC ( C depletion in C grassland soil and C enrichment in C forest soil compared to the corresponding vegetation). In this regard, the isotopic difference between roots and aboveground biomass was not relevant, but may become more important at greater soil depths. C depletion of VSC lignins relative to OC was higher in C -biomass and C -derived SOC compared to the C counterparts. As lignin contents of heavy fractions were low, in particular for those with C isotopic signature, the influence of lignin on OC δ C values in grassland topsoils is presumably low. Rather, the presence of charred grass residues and the accumulation of alkyl C in heavy fractions as revealed by C NMR spectroscopy contribute to decreasing δ C values from grass biomass to C -derived heavy fractions. In forest topsoils, the accumulation of C depleted VSC lignin residues in heavy fractions counteracts the prevailing C enrichment of OC from plant biomass to heavy fractions. Nonetheless, non-lignin compounds with relatively high C contents like microbial-derived OC have a stronger influence on δ C values of OC in forest soils than lignins or aliphatic biopolymers. The mineral-associated SOC is in a late phase of decomposition with large contributions of microbial-derived carbohydrates, but distinct structural and isotopical alterations of lignin between C - and C -derived heavy fractions. This may indicate different processes and/or extent of lignin (and SOM) biodegradation between C grassland and C forest resulting from other kind of decomposer communities in association with distinct types and amounts of plant input as source of SOM and thus, carbon source for microbial transformation. Our results indicate that the importance of lignin for δ C values of OC was overestimated in previous studies, at least in subtropical C grassland and C forest topsoils. ► Lignin and SOC showed C enrichment in C forest and C depletion in C grassland. ► Low influence of lignin on δ C values of SOC in C grassland soils. ► C depleted lignin counteracts the prevailing C enrichment of SOC in forest soils. ► C enriched non-lignin compounds strongly influence δ C values in C forest soils. ► Structural and isotopical degradation of lignin differs between grassland and forest.
    Keywords: 13c/12c ; Soil Organic Matter ; 13c NMR Spectroscopy ; Cuo Oxidation ; Gc/C-Irms ; Carbohydrates ; Brazil ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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