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  • 1
    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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  • 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: 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: Nature, 2011, Vol.478(7367), p.49
    Description: Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming. Journal Article.
    Keywords: Environmental Sciences Geosciences;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 5
    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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  • 6
    In: Global Change Biology, October 2015, Vol.21(10), pp.3836-3845
    Description: Organic carbon () sequestration in degraded semi‐arid environments by improved soil management is assumed to contribute substantially to climate change mitigation. However, information about the soil organic carbon () sequestration potential in steppe soils and their current saturation status remains unknown. In this study, we estimated the storage capacity of semi‐arid grassland soils on the basis of remote, natural steppe fragments in northern China. Based on the maximum saturation of silt and clay particles 〈20 μm, sequestration potentials of degraded steppe soils (grazing land, arable land, eroded areas) were estimated. The analysis of natural grassland soils revealed a strong linear regression between the proportion of the fine fraction and its content, confirming the importance of silt and clay particles for stabilization in steppe soils. This relationship was similar to derived regressions in temperate and tropical soils but on a lower level, probably due to a lower C input and different clay mineralogy. In relation to the estimated storage capacity, degraded steppe soils showed a high saturation of 78–85% despite massive losses due to unsustainable land use. As a result, the potential of degraded grassland soils to sequester additional was generally low. This can be related to a relatively high contribution of labile , which is preferentially lost in the course of soil degradation. Moreover, wind erosion leads to substantial loss of silt and clay particles and consequently results in a direct loss of the ability to stabilize additional . Our findings indicate that the loss in semi‐arid environments induced by intensive land use is largely irreversible. Observed increases after improved land management mainly result in an accumulation of labile prone to land use/climate changes and therefore cannot be regarded as contribution to long‐term sequestration.
    Keywords: Climate Change ; Fine Fraction ; Soil Organic Carbon ; Soil Texture ; Steppe Soils
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 7
    In: Global Change Biology, April 2018, Vol.24(4), pp.1637-1650
    Description: Global change contributes to the retreat of glaciers at unprecedented rates. The deglaciation facilitates biogeochemical processes on glacial deposits with initiating soil formation as an important driver of evolving ecosystems. The underlying mechanisms of soil formation and the association of soil organic matter () with mineral particles remain unclear, although further insights are critical to understand carbon sequestration in soils. We investigated the microspatial arrangement of coatings at intact soil microaggregate structures during various stages of ecosystem development from 15 to 〉700 years after deglaciation in the proglacial environment of the Damma glacier (Switzerland). The functionally important clay‐sized fraction (2.2 g/cm). To quantify how extends across the surface of mineral particles (coverage) and whether coatings are distributed in fragmented or connected patterns (connectivity), we developed an image analysis protocol based on nanoscale secondary ion mass spectrometry (Nano). We classified and mineral areas depending on the O, C, and CN distributions. With increasing time after glacial retreat, the microspatial coverage and connectivity of increased rapidly. The rapid soil formation led to a succession of patchy distributed to more connected coatings on soil microaggregates. The maximum coverage of 55% at 〉700 years suggests direct evidence for sequestration being decoupled from the mineral surface, as it was not completely masked by and retained its functionality as an ion exchange site. The chemical composition of coatings showed a rapid change toward a higher :C ratio already at 75 years after glacial retreat, which was associated with microbial succession patterns reflecting high N assimilation. Our results demonstrate that rapid sequestration drives the microspatial succession of coatings in soils, a process that can stabilize for the long term. The pronounced retreat of glaciers due to climate change leads to the exposure of glacial deposits where initial soil formation starts along with the accrual of soil carbon. Soil organic matter (SOM) coatings at soil microaggregates were investigated in a chronosequence of soils 15 to 〉700 years after glacial retreat at the Damma glacier (Switzerland). Our results show a rapidly increasing coverage of mineral surfaces by SOM up to a maximum of 55% and a development from patchy distributed to more connected SOM coatings. The microspatial patterns of SOM coatings shaped the sequestration of SOM and partially decoupled it from the mineral particle surfaces, which retain their functionality as an ion exchange sites.
    Keywords: Biogeochemical Soil Interfaces ; Glacier Forefield ; Mineral‐Associated Organic Matter ; Nanoscale Secondary Ion Mass Spectrometry ; Organic Coating ; Organo‐Mineral Associations ; Soil Carbon Sequestration ; Spatial Complexity
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 8
    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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  • 9
    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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  • 10
    Language: English
    In: Plant and Soil, 2011, Vol.338(1), pp.63-81
    Description: Grazed steppe ecosystems are discussed as one of the big global carbon sinks that may have the potential to sequester large amounts of atmospheric CO 2 and mitigate the effects of global change if grazing is abandoned or management improved. But until today, little is known about sequestration potentials and stabilisation mechanisms in complete soil profiles of semiarid grasslands and how these systems react to grazing cessation. We applied a combined aggregate size, density and particle size fractionation procedure to sandy steppe soils under different grazing intensities (continuously grazed = Cg, winter grazing = Wg, ungrazed since 1999 = Ug99, ungrazed since 1979 = Ug79). Higher inputs of organic matter in ungrazed treatments led to higher amounts of OC in coarse aggregate size classes (ASC) and especially in particulate organic matter (POM) fractions across all depth. These processes started in the topsoil and took more than 5 years to reach deeper soil horizons (〉10 cm). After 25 years of grazing cessation, subsoils showed clearly higher POM amounts. We found no grazing-induced changes of soil organic matter (SOM) quantity in fine ASC and particle size fractions. Current C-loading of fine particle size fractions was similar between differently grazed plots and decreased with depth, pointing towards free sequestration capacities in deeper horizons. Despite these free capacities, we found no increase in current C-loading on fine mineral soil fractions after 25 years of grazing exclusion. Silt and clay fractions appeared to be saturated. We suppose empirical estimations to overestimate sequestration potentials of particle size fractions or climatic conditions to delay the decomposition and incorporation of OM into these particle size fractions. POM quality was analysed using solid-state 13 C NMR spectroscopy to clarify if grazing cessation changed chemical composition of POM in different ASC and soil depths via changing litter quality or changing decomposition dynamics. We found comparable POM compositions between different grazing intensities. POM is decomposed hierarchically from coarse to fine particles in all soil depths and grazing cessation has not affected the OM decomposition processes. The surplus of OM due to grazing cessation was predominately sequestered in readily decomposable POM fractions across all affected horizons. We question the long-term stabilisation of OM in these steppe soils during the first 25 years after grazing cessation and request more studies in the field of long-term OM stabilisation processes and assessment of carbon sequestration capacities to consider deeper soil horizons.
    Keywords: Solid-state C NMR spectroscopy ; SOM composition ; Carbon loading ; SOM sequestration ; Grazing ; Physical fractionation
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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