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  • 1
    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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  • 2
    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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  • 3
    Language: English
    In: Plant and Soil, 2011, Vol.340(1), pp.7-24
    Description: Spatial prediction of soil organic matter is a global challenge and of particular importance for regions with intensive land use and where availability of soil data is limited. This study evaluated a Digital Soil Mapping (DSM) approach to model the spatial distribution of stocks of soil organic carbon (SOC), total carbon (C tot ), total nitrogen (N tot ) and total sulphur (S tot ) for a data-sparse, semi-arid catchment in Inner Mongolia, Northern China. Random Forest (RF) was used as a new modeling tool for soil properties and Classification and Regression Trees (CART) as an additional method for the analysis of variable importance. At 120 locations soil profiles to 1 m depth were analyzed for soil texture, SOC, C tot , N tot , S tot , bulk density (BD) and pH. On the basis of a digital elevation model, the catchment was divided into pixels of 90 m × 90 m and for each cell, predictor variables were determined: land use unit, Reference Soil Group (RSG), geological unit and 12 topography-related variables. Prediction maps showed that the highest amounts of SOC, C tot , N tot and S tot stocks are stored under marshland, steppes and mountain meadows. River-like structures of very high elemental stocks in valleys within the steppes are partly responsible for the high amounts of SOC for grasslands (81–84% of total catchment stocks). Analysis of variable importance showed that land use, RSG and geology are the most important variables influencing SOC storage. Prediction accuracy of the RF modeling and the generated maps was acceptable and explained variances of 42 to 62% and 66 to 75%, respectively. A decline of up to 70% in elemental stocks was calculated after conversion of steppe to arable land confirming the risk of rapid soil degradation if steppes are cultivated. Thus their suitability for agricultural use is limited.
    Keywords: Classification and Regression Trees (CART) ; Soil organic carbon (SOC) ; China ; Grassland
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    In: Global Change Biology, February 2017, Vol.23(2), pp.933-944
    Description: Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of . Here, we used size‐density fractionation and solid‐state C‐ spectroscopy to explore the extent to which declines in microbial decay in a long‐term (. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; ); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N‐alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine‐texture forest soils.
    Keywords: 13 C‐ Nmr ; Anthropogenic N Deposition ; Particulate Organic Matter ; Soil C Storage ; Soil Organic Matter
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 5
    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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  • 6
    Language: English
    In: Plant and Soil, 2014, Vol.381(1), pp.95-110
    Description: Background and aims Differences in chemical composition of root compounds and root systems among tree species may affect organic matter (OM) distribution, source and composition in forest soils. The objective of this study was to elucidate the contribution of species specific cutin and suberin biomarkers as proxies for shoot- and root-derived organic carbon (OC) to soil OM at different depths with increasing distance to the stems of four different tree species. Methods The contribution of cutin- and suberin-derived lipids to OM in a Cutanic Alisol was analyzed with increasing soil depth and distance to the stems of Fagus sylvatica L., Picea abies (L.) Karst., Quercus robur L. and Pseudotsuga menziesii (Mirb.) Franco. Cutin and suberin monomers of plants and soils were analyzed by alkaline hydrolysis and subsequent gas chromatography-mass spectrometry. Results The amount and distribution of suberin-derived lipids in soil clearly reflected the specific root system of the different tree species. The amount of cutin-derived lipids decreased strongly with soil depth, indicating that the input of leaf/needle material is restricted to the topsoil. In contrast to the suberin-derived lipids, the spatial pattern of cutin monomer contribution to soil OM did not depend on tree species. Conclusions Our results document the importance of tree species as a main factor controlling the composition and distribution of OM in forest soils. They reveal the impact of tree species on root-derived OM distribution and the necessity to distinguish among different zones when studying soil OM storage in forests. Keywords Biomarkers * Cutin * Suberin * Depth profile * Subsoil
    Keywords: Biomarkers ; Cutin ; Suberin ; Depth profile ; Subsoil
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    In: PLoS ONE, 2014, Vol.9(12)
    Description: Ongoing climate change will lead to more extreme weather events, including severe drought periods and intense drying rewetting cycles. This will directly influence microbial nitrogen (N) turnover rates in soil by changing the water content and the oxygen partial pressure. Therefore, a space for time climate change experiment was conducted by transferring intact beech seedling-soil mesocosms from a northwest (NW) exposed site, representing today's climatic conditions, to a southwest (SW) exposed site, providing a model climate for future conditions with naturally occurring increased soil temperature (+0.8°C in average). In addition, severe drought and intense rainfall was simulated by a rainout shelter at SW and manual rewetting after 39 days drought, respectively. Soil samples were taken in June, at the end of the drought period (August), 24 and 72 hours after rewetting (August) and after a regeneration period of four weeks (September). To follow dynamics of bacterial and archaeal communities involved in N turnover, abundance and activity of nitrifiers, denitrifiers, N 2 -fixing microbes and N-mineralizers was analyzed based on marker genes and the related transcripts by qPCR from DNA and RNA directly extracted from soil. Abundance of the transcripts was reduced under climate change with most pronounced effects for denitrification. Our results revealed that already a transfer from NW to SW without further treatment resulted in decreased cnor and nosZ transcripts, encoding for nitric oxide reductase and nitrous oxide reductase, respectively, while nirK transcripts, encoding for nitrite reductase, remained unaffected. Severe drought additionally led to reduced nirK and cnor transcripts at SW. After rewetting, nirK transcripts increased rapidly at both sites, while cnor and nosZ transcripts increased only at NW. Our data indicate that the climate change influences activity pattern of microbial communities involved in denitrification processes to a different extend, which may impact emission rates of the greenhouse gas N 2 O.
    Keywords: Research Article ; Biology And Life Sciences ; Ecology And Environmental Sciences
    E-ISSN: 1932-6203
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  • 8
    In: Global Change Biology, February 2014, Vol.20(2), pp.653-665
    Description: Sequestration of atmospheric carbon (C) in soils through improved management of forest and agricultural land is considered to have high potential for global mitigation. However, the potential of soils to sequester soil organic carbon () in a stable form, which is limited by the stabilization of against microbial mineralization, is largely unknown. In this study, we estimated the C sequestration potential of soils in southeast Germany by calculating the potential saturation of silt and clay particles according to Hassink [ (1997) 77] on the basis of 516 soil profiles. The determination of the current content of silt and clay fractions for major soil units and land uses allowed an estimation of the C saturation deficit corresponding to the long‐term C sequestration potential. The results showed that cropland soils have a low level of C saturation of around 50% and could store considerable amounts of additional . A relatively high C sequestration potential was also determined for grassland soils. In contrast, forest soils had a low C sequestration potential as they were almost C saturated. A high proportion of sites with a high degree of apparent oversaturation revealed that in acidic, coarse‐textured soils the relation to silt and clay is not suitable to estimate the stable C saturation. A strong correlation of the C saturation deficit with temperature and precipitation allowed a spatial estimation of the C sequestration potential for Bavaria. In total, about 395 Mt CO‐equivalents could theoretically be stored in A horizons of cultivated soils – four times the annual emission of greenhouse gases in Bavaria. Although achieving the entire estimated C storage capacity is unrealistic, improved management of cultivated land could contribute significantly to mitigation. Moreover, increasing stocks have additional benefits with respect to enhanced soil fertility and agricultural productivity.
    Keywords: Agricultural Management ; Climate Change ; Mitigation ; Soil Organic Carbon Stocks ; Soil Fractionation ; Stabilization Of Soil Organic Matter
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 9
    Language: English
    In: Soil Biology and Biochemistry, November 2014, Vol.78, pp.263-273
    Description: To better understand how carbon and nitrogen mineralization are linked in soils, we conducted a long-term incubation experiment and compared carbon and nitrogen dynamics in the bulk soil and in soil fractions. Topsoil of a Rendzic Leptosol from a beech forest site near Tuttlingen, Germany, was separated into three particle size classes: sand (2000–20 μm), silt (20–2 μm), and clay (〈2 μm). Bulk soil and particle size fractions were incubated in replicate, allowing periodic destructive sampling of triplicates at day 0, 14, 42, 84, 140, 210, and 280. We monitored CO –C respiration, NH –N emissions, nitrogen mineralization, pool sizes of total and salt extractable (0.01 M CaCl ) organic carbon and nitrogen, and microbial biomass carbon and nitrogen. The chemical composition of selected samples was further characterized by C-NMR spectroscopy. Fractionation did not influence carbon mineralization (∑ fractions ≈ bulk soil), which decreased in the order sand 〉 clay 〉 silt. The fractions respired between 10.4% (sand fraction), 8.8% (clay fraction) and 4.4% (silt fraction) of total soil organic carbon. However, nitrogen mineralization was affected by the fractionation procedure (∑ fractions 〈 bulk soil) and followed the order clay 〉 silt 〉 sand. Fractionation increased the surface area and hence provided accessory mineral surfaces, which allowed new binding of especially nitrogen-rich compounds, in addition to ammonium fixation via cation exchange. As indicated by lower metabolic quotients, microbial carbon mineralization was more efficient in the bulk soil compared to the calculated sum of fractions. In the clay fraction, carbon mineralization rates, salt extractable organic carbon contents, and microbial biomass carbon and nitrogen contents declined strongly towards the end of the incubation. This indicates that in the clay fraction, organic carbon was not available for microbial degradation and that microorganisms were strongly carbon-limited causing a subsequent inhibition of nitrogen immobilization. Density fractionation revealed that organic matter in the sand fraction consisted mainly of particulate organic matter present as light material containing partly decomposed plant remnants. The organic matter in the clay fraction was mostly adsorbed on mineral surfaces. Organic matter in the sand and in the clay fraction was dominated by O/N-alkyl C indicating low recalcitrance, but the C/N ratio of organic matter narrowed with decreasing particle size. Our results suggest that carbon and nitrogen mineralization are decoupled in the mineral-associated fractions of the soil. The specific interactions of both carbon and nitrogen containing components with the mineral matrix strongly modulate the mineralization dynamics. Therefore, isolated considerations of C/N or alkyl C to O/N-alkyl C ratios of organic matter are insufficient as indicators for decomposition in plant residues. The combined consideration of C/N and alkyl C to O/N-alkyl C ratios provides a first impression about the degree of decomposition in plant residues. However, bioavailability in fractions where organic matter is mainly stabilized by spatial inaccessibility and by organo-mineral interactions cannot be explained by these ratios, but can be examined by an incubation approach.
    Keywords: Laboratory Incubation ; Som Stabilization ; Rendzic Leptosol ; European Beech ; Heterotrophic Respiration ; NMR ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 10
    Language: English
    In: Plant and Soil, 2013, Vol.369(1), pp.657-668
    Description: Aims: Our aims were to characterize the fate of leaf-litter-derived nitrogen in the plant-soil-microbe system of a temperate beech forest of Southern Germany and to identify its importance for N nutrition of beech seedlings. Methods: super(15)N-labelled leaf litter was traced in situ into abiotic and biotic N pools in mineral soil as well as into beech seedlings and mycorrhizal root tips over three growing seasons. Results: There was a rapid transfer of super(15)N into the mineral soil already 21 days after tracer application with soil microbial biomass initially representing the dominant litter-N sink. However, super(15)N recovery in non-extractable soil N pools strongly increased over time and subsequently became the dominant super(15)N sink. Recovery in plant biomass accounted for only 0.025 % of super(15)N excess after 876 days. After three growing seasons, super(15)N excess recovery was characterized by the following sequence: non-extractable soil N〉〉extractable soil N including microbial biomass〉〉plant biomass〉ectomycorrhizal root tips. Conclusions: After quick vertical dislocation and cycling through microbial N pools, there was a rapid stabilization of leaf-litter-derived N in non-extractable N pools of the mineral soil. Very low super(15)N recovery in beech seedlings suggests a high importance of other N sources such as root litter for N nutrition of beech understorey.
    Keywords: Nitrogen cycling ; Beech ; 15N-labelled leaf litter ; 15N tracing ; Microbial biomass ; Ectomycorrhiza
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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