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  • Soil Biology and Biochemistry  (24)
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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: 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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  • 3
    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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  • 4
    Language: English
    In: Soil Biology and Biochemistry, 2010, Vol.42, pp.379-382
    Keywords: Environmental Sciences ; Agriculture ; Environmental Sciences ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
    Source: Hyper Article en Ligne (CCSd)
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  • 5
    Language: English
    In: Soil Biology and Biochemistry, December 2014, Vol.79, pp.57-67
    Description: The study of interactions between minerals, organic matter (OM) and microorganisms is essential for the understanding of soil functions such as OM turnover. Here, we present an interdisciplinary approach using artificial soils to study the establishment of the microbial community and the formation of macro-aggregates as a function of the mineral composition by using artificial soils. The defined composition of a model system enables to directly relate the development of microbial communities and soil structure to the presence of specific constituents. Five different artificial soil compositions were produced with two types of clay minerals (illite, montmorillonite), metal oxides (ferrihydrite, boehmite) and charcoal incubated with sterile manure and a microbial community derived from a natural soil. We used the artificial soils to analyse the response of these model soil systems to additional sterile manure supply (after 562 days). The artificial soils were subjected to a prolonged incubation period of more than two years (842 days) in order to take temporally dynamic processes into account. In our model systems with varying mineralogy, we expected a changing microbial community composition and an effect on macro-aggregation after OM addition, as the input of fresh substrate will re-activate the artificial soils. The abundance and structure of 16S rRNA gene and internal transcribed spacer (ITS) fragments amplified from total community DNA were studied by quantitative real-time PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE), respectively. The formation of macro-aggregates (〉2 mm), the total organic carbon (OC) and nitrogen (N) contents, the OC and N contents in particle size fractions and the CO respiration were determined. The second manure input resulted in higher CO respiration rates, 16S rRNA gene and ITS copy numbers, indicating a stronger response of the microbial community in the matured soil-like system. The type of clay minerals was identified as the most important factor determining the composition of the bacterial communities established. The additional OM and longer incubation time led to a re-formation of macro-aggregates which was significantly higher when montmorillonite was present. Thus, the type of clay mineral was decisive for both microbial community composition as well as macro-aggregation, whereas the addition of other components had a minor effect. Even though different bacterial communities were established depending on the artificial soil composition, the amount and quality of the OM did not show significant differences supporting the concept of functional redundancy.
    Keywords: Dgge ; Illite ; Montmorillonite ; Decomposition ; Respiration ; Soil Formation ; 16s Rrna Gene ; Its Fragment ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 6
    Language: English
    In: Soil Biology and Biochemistry, February 2014, Vol.69, pp.168-178
    Description: The stabilization of soil organic matter (SOM) is triggered by three main mechanisms: (i) low bioavailability due to aggregation, (ii) recalcitrance due to the chemical structure, and (iii) association of the SOM with mineral surfaces. In the present study we used particle size SOM fractions (sand, silt and clay), derived from the Ah soil horizon from a Norway spruce forest in Southern Germany, to study the effects of different stabilization mechanisms on the bioavailability of soil organic carbon (SOC) in a one year incubation experiment. The respired CO was hourly recorded, additionally CO was analysed 20 times and CO three times during the incubation experiment. To better differentiate between particulate OM (POM) and mineral associated OM (MIN), the incubated fractions and bulk soil were separated according to density (1.8 g cm ) after the incubation experiment. C-CPMAS NMR spectroscopy was used to study the chemical composition of the incubated samples. We demonstrate a clear increase in SOM bioavailability due to aggregate disruption, as the calculated theoretical CO evolution of the SOM fractions recombined by calculation was 43.8% higher in relation to the intact bulk soil. The incubated sand fraction, dominated by POM rich in O/N-alkyl C, showed a prolonged bioavailability of SOC moieties with mean residence times (MRT) of 78 years. Interestingly, the silt fraction, dominated by highly aliphatic, more recalcitrant POM, showed low mineralization rates and slow MRT's (192 years) close to values for the clay fraction (171 years), which contained a large amount of mineral-associated SOM. The recorded CO signatures showed a high depletion in C during the initial stage of the incubation, but an enrichment of the respired CO of up to 3.4‰ relative to the incubated SOM was observed over longer time periods (after 3 and 4 days for bulk soil and sand, respectively, and after 14 days for silt and clay). Therefore, we found no evidence for a C enrichment of SOM as driven by metabolic isotopic fractionation during microbial SOM mineralization, but an indication of a change in the isotopic composition of the C-source over time.
    Keywords: 13co2 ; 14co2 ; Laboratory Incubation ; Heterotrophic Respiration ; 13c-Cpmas NMR Spectroscopy ; Particle Size Fractionation ; Density Fractionation ; Mean Residence Time ; Microbial Biomass ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 7
    Language: English
    In: Soil Biology and Biochemistry, December 2013, Vol.67, pp.55-61
    Description: Despite their importance for C sequestration, especially in the subsoil, little is known about decomposition and stabilisation processes affecting root litter in soil horizons at different depths. In particular the influence of specific conditions at depth on molecular alterations of degrading root litter is unknown. We took advantage of a decomposition experiment, which was carried out at different soil depths under field conditions and sampled litterbags with C-labelled wheat roots, incubated in subsoil horizons at 30, 60 and 90 cm depth for up to 36 months. Changes of bulk root chemistry were studied by solid-state C NMR spectroscopy, and lignin content and composition was assessed after CuO oxidation. Compound-specific isotope analysis allowed assessment of the role of root lignin for soil C storage at the different soil depths. Results indicated that decomposition proceeded in a similar way at all three depths, but at a different rate. The alkyl/O-alkyl C ratio was a meaningful indicator to assess the degree of root litter degradation within the mineral soil. After three years, the greatest increase of this ratio, corresponding to the most advanced degradation degree, occurred at 30 cm compared to the lower depths despite a similar carbon loss. The greater proportion of O-alkyl C persisting in deeper subsoil horizons was consistent with their higher clay content. Root derived lignin-C concentration decreased at all soil depths and soil lignin content reached a similar level after 12 months, suggesting that microbial communities in all subsoil depths had capability to degrade lignin. However, the intensity of degradation appeared to be different at different soil depths, with lignin being less transformed at 60 and 90 cm depth. We conclude that chemistry of subsoil organic matter is determined by horizon-specific conditions, which have to be fully understood in order to explain the long residence times of subsoil C. In our study physico-chemical parameters only partly explained the observations.
    Keywords: Solid-State13c NMR Spectroscopy ; 13c Enriched Lignin ; Gc/C/Irms ; Subsoil ; Roots ; Wheat ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 8
    Language: English
    In: Soil Biology and Biochemistry, July 2018, Vol.122, pp.19-30
    Description: Despite a large body of studies investigating soil organic carbon (SOC) stocks and potential influencing factors, the impact of contrasting parent material, particularly in the subsoil, has received little attention. To reveal potential effects varying parent materials exert on SOC stocks, we investigated chemical ( C content and overall chemical composition via C NMR spectroscopy) and plant/microbial related parameters (root mass, amino sugars) of bulk soil and soil organic matter fractions from topsoil, subsoil, and rhizosphere soil at three European beech stands ( L.) only differing in parent material (Tertiary sand, Quaternary loess, and Tertiary basalt). The results suggest that the clay fraction, its amount being largely dependent on the respective parent material, took a central role in shaping differences in SOC stocks among the investigated sites by affecting soil organic matter stabilization via organo-mineral association and aggregation. This fraction was particularly relevant in the subsoil, where it accounted for up to 80% of the bulk soil SOC stocks that decreased with decreasing amounts of the clay fraction (basalt 〉 loess 〉 sand site). Determining the soil's nutrient composition, parent material likely also indirectly affected SOC stocks by changing rhizosphere traits (such as fine root density or mortality) and by attracting root growth (and thus organic matter inputs) to subsoil with higher nutrient contents, where root inputs in the form of rhizodeposits were likely the prime source of plant-derived SOC. However, root inputs also contributed in large part to topsoil SOC stocks and were associated with higher abundance of microbial compounds (amino sugars), whose relative importance increased with increasing soil depth. Independent of soil depth and site, amino sugars and the amount of the clay fraction, combined with parameters related to the input of organic matter (root mass and amount of the particulate organic matter fraction) explained more than 90% of the variability in SOC stocks, indicating a key role of these measures in impacting SOC stocks. Because parent material directly or indirectly influenced these parameters, we demonstrate the necessity to consider differences in parent material when estimating and predicting SOC stocks.
    Keywords: Fagus Sylvatica L ; 14c ; Physical Fractionation ; Amino Sugars ; 13c NMR ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 9
    Language: English
    In: Soil Biology and Biochemistry, March 2013, Vol.58, pp.323-331
    Description: Our main objective was to trace and to quantify the stabilization of nitrogen released from litter decomposition in different functional soil organic matter fractions. To identify the fate of nitrogen in a free-range experiment, N-labeled beech litter was deposited on the bare soil surface of three 2 m × 2 m plots on a Rendzic Leptosol under beech ( L.) with mull humus form near Tuttlingen (Swabian Jura, Germany). The N composition of bulk soil and soil fractions was monitored for three years by sampling the litter layer and the Ah horizon (0–5, 5–10 cm) after 140, 507, and 876 d. A combined density and particle size fractionation procedure allowed the isolation of different functional soil organic matter fractions: free light fraction, occluded organic matter, and organo-mineral associations. The first flush in the N enrichment was observed in the bulk soil within 140 d, due to plant debris transferred to the free light fraction by probably bioturbation and soluble compounds being leached from the litter directly to the clay fractions. The observed rates within the first 140 d indicated a quick transfer of N-enriched compounds from litter into the free light fraction, with a rate of 0.07 μg kg  d , and to the clay fractions, with a rate of 0.31 μg kg  d . In contrast, transfer to the occluded light fractions was delayed, with rates of 0.01 μg kg  d (〉 20 μm) and 0.001 μg kg  d (〈 20 μm), respectively. After 876 d, we recovered 9% of the added label in the 0–10 cm soil horizon, of which more than 4% was found in the organo-mineral fraction (0–5 cm), nearly 3% in the light fractions (0–5 cm), and another 2% unspecified in the bulk soil of 5–10 cm depth. We therefore conclude that the clay fractions act as the main sink for the recovered N. The rapid incorporation and the high preservation of N in the clay fractions revealed the dominant role of organo-mineral associations in the stabilization of nitrogen in the investigated soil. ► Rapid transfer of N from litter into the clay fractions completed within 140 days. ► Dominant role of fine organo-mineral associations for stabilization of nitrogen. ► Occluded organic matter is protected by slow aggregate turnover. ► After 876 d, we recovered 9% of the added N label in the mineral soil (0–10 cm).
    Keywords: 15n ; Physical Fractionation ; Light Fraction ; Organo-Mineral Fraction ; Clay ; Fagus Sylvatica L ; Nitrogen Storage ; Field Experiment ; Transfer Rates ; Decomposition ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 10
    Language: English
    In: Soil Biology and Biochemistry, January 2014, Vol.68, pp.241-251
    Description: Prolonged summer droughts are projected to occur as a consequence of climate change in Central Europe. The resulting reduced soil water availability may lead to alterations in rates of soil processes such as nitrogen partitioning among soil organic matter fractions and stabilization within soil. To study the effect of climate change-induced drought on (1) the distribution of nitrogen among soil organic matter fractions and (2) nitrogen stabilization, we performed a space-for-time climate change experiment. We transferred intact plant–soil–microbe mesocosms of a Rendzic Leptosol with a young beech tree from a slope with northwestern exposure in southern Germany characterized by a cool-moist microclimate across a narrow valley to a slope with southwestern exposure with a warm-dry microclimate, which reflects projected future climatic conditions. A control transfer was also done on the northwest-facing slope within the same area of origin. We combined a homogenous N labeling approach using ammonium nitrate with a physical fractionation procedure and chemical soil extraction protocols. Our aim was to follow the partitioning of N in different soil organic matter fractions, i.e. light fractions, organo-mineral fractions, and extractable soil fractions including microbial biomass, ammonium, nitrate, and dissolved organic nitrogen. Within less than one growing season, we observed a modified partitioning of recently applied inorganic N between different soil fractions in relation to drier summer conditions, with attenuated nitrogen turnover under drought and consequently significantly higher N concentrations in the relatively labile light fractions. We ascribed this effect to a decelerated mineralization immobilization turnover. We conclude that prolonged summer droughts may alter the stabilization dynamics because the induced inactivity of microorganisms may reduce the transfer of nitrogen to stabilization pathways. A retarded stabilization in organo-mineral associations enhances the risk of nitrogen losses during extreme rainfall events, which are projected to increase in the 21st century predicted by future climate change scenarios for Central Europe.
    Keywords: Nitrogen Stabilization ; Density Fractionation ; 15n Labeling ; Climate Change ; Fagus Sylvatica L ; Field Experiment ; Light Fraction ; Microbial Biomass ; Mineralization Immobilization Turnover ; Transplant Study ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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