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  • Organic Carbon
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  • 1
    Language: English
    In: Organic Geochemistry, 2006, Vol.37(11), pp.1573-1589
    Description: The mechanisms of organic matter (OM) stabilization and possible organic–mineral interactions in alkaline soils rich in Ca (calcareous soils) were investigated. We sampled soils that developed over a period of 70 years under natural succession from homogeneous calcareous and organic-free substrate resulting from industrial production. We took advantage of a shift from non-woody to woody angiosperm vegetation with increasing soil age and tracked lignin as an indicator of the fate of plant residues. Using density separation in combination with ultrasonic dispersion, four fractions were obtained: (1) free particulate OM (FPOM), (2) OM occluded within soil aggregates (OPOM), (3) heavy fraction with a density of 1.6–2.2 g cm and (4) heavy fraction with a density 〉2.2 g cm . The fractions were analysed for C, N, CuO oxidation products and mineral composition. Accumulation of OM by occlusion within aggregates contributed little (4–16%) to the total organic C in the soils. The dominant portion of organic C was in the fractions 〉1.6 g cm . Lignin phenols in the fractions 〉1.6 g cm showed the most intensive diagenetic alteration as reflected in small yields of vanillic, syringic and cinnamic (VSC) lignin and stronger oxidation of the side chains of vanillyl phenols. In contrast to the POM fractions, the fractions 〉1.6 g cm from the older sites conserved the non-woody angiosperm lignin signature of the former vegetation, indicating slower OM turnover. The mineral composition of the two heavy fractions clearly differed, with layered double hydroxides (i.e., hydrotalcite and hydrocalumite) dominating the fractions 〉1.6 g cm and calcite dominating the fractions 〉2.2 g cm . We conclude that partly degraded lignin, enriched in acidic groups, accumulated in the fraction 1.6–2.2 g cm , due to preferential adsorption to the positively charged layered double hydroxides. Although representing only a small portion of the soil mineral assemblage, layered double hydroxides seem to be of significant relevance for OM accumulation. Over the years, the fraction 1.6–2.2 g cm comprised the largest single pool of organic C. Compared with the 1.6–2.2 g cm fraction, the 〉2.2 g cm fraction had a much smaller carbon concentrations. The lignin in that fraction showed by far the strongest oxidative alteration of all the fractions. We assume that partly degraded lignin components, not adsorbed to layered double hydroxides, undergo further microbial oxidation until they form complexes with calcite. Consequently, we conclude that in these calcareous soils accumulation of OM is mainly due to the attachment of partly oxidized OM to positively charged clays, resulting in stabilization against further decomposition, thus slowing down turnover. To a minor extent, calcite is also involved in the stabilization of the plant residues.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 2
    In: Global Change Biology, January 2018, Vol.24(1), pp.e183-e189
    Description: Current climate and land‐use changes affect regional and global cycles of silicon (Si), with yet uncertain consequences for ecosystems. The key role of Si in marine ecology by controlling algae growth is well recognized but research on terrestrial ecosystems neglected Si since not considered an essential plant nutrient. However, grasses and various other plants accumulate large amounts of Si, and recently it has been hypothesized that incorporation of Si as a structural plant component may substitute for the energetically more expensive biosynthesis of lignin. Herein, we provide evidence supporting this hypothesis. We demonstrate that in straw of rice () deriving from a large geographic gradient across South‐East Asia, the Si concentrations (ranging from 1.6% to 10.7%) are negatively related to the concentrations of carbon (31.3% to 42.5%) and lignin‐derived phenols (32 to 102 mg/g carbon). Less lignin may explain results of previous studies that Si‐rich straw decomposes faster. Hence, Si seems a significant but hardly recognized factor in organic carbon cycling through grasslands and other ecosystems dominated by Si‐accumulating plants. The key role of silicon in marine ecology by controlling algae growth is well recognized but research on terrestrial ecosystems neglected Si since not considered an essential plant nutrient. However, many plants accumulate large amounts of Si, and recently it has been hypothesized that incorporation of Si as a structural component may substitute for the energetically more expensive biosynthesis of lignin. Herein, we provide evidence supporting this hypothesis. We demonstrate that in rice straw deriving from a large geographic gradient across South‐East Asia, the Si concentrations are negatively related to the concentrations of carbon and lignin‐derived phenols. Our data offer an explanation for previous findings of faster decomposition of Si‐rich rice straw as lignin regulates plant litter decomposition rates. Hence, Si seems a significant but hardly recognized factor in carbon cycling through ecosystems dominated by grass species and/or other Si‐accumulating plants.
    Keywords: Carbon Cycle ; Lignin ; Litter Decomposition ; Rice ; Silicon ; Structural Plant Components
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 3
    In: Global Change Biology, April 2013, Vol.19(4), pp.1107-1113
    Description: More than 50% of the world's population feeds on rice. Soils used for rice production are mostly managed under submerged conditions (paddy soils). This management, which favors carbon sequestration, potentially decouples surface from subsurface carbon cycling. The objective of this study was to elucidate the long‐term rates of carbon accrual in surface and subsurface soil horizons relative to those of soils under nonpaddy management. We assessed changes in total soil organic as well as of inorganic carbon stocks along a 2000‐year chronosequence of soils under paddy and adjacent nonpaddy management in the angtze delta, hina. The initial organic carbon accumulation phase lasts much longer and is more intensive than previously assumed, e.g., by the ntergovernmental anel on limate hange (). Paddy topsoils accumulated 170–178 kg organic carbon ha a in the first 300 years; subsoils lost 29–84 kg organic carbon ha a during this period of time. Subsoil carbon losses were largest during the first 50 years after land embankment and again large beyond 700 years of cultivation, due to inorganic carbonate weathering and the lack of organic carbon replenishment. Carbon losses in subsoils may therefore offset soil carbon gains or losses in the surface soils. We strongly recommend including subsoils into global carbon accounting schemes, particularly for paddy fields.
    Keywords: Carbon Sequestration ; Inorganic Carbon ; Land Use ; Organic Carbon ; Paddy ; Rice Cultivation ; Soils ; Subsoils
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, 2007, Vol.71(10), pp.2569-2590
    Description: Mineral-associated organic matter (OM) represents a large reservoir of organic carbon (OC) in natural environments. The factors controlling the extent of the mineral-mediated OC stabilization, however, are poorly understood. The protection of OM against biodegradation upon sorption to mineral phases is assumed to result from the formation of strong bonds that limit desorption. To test this, we studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as ‘ligand exchange’, ‘Ca bridging’, and ‘van der Waals forces’. Organic matter extracted from an Oa forest floor horizon under Norway spruce ( (L.) Karst) was reacted with minerals at dissolved OC concentrations of ∼5–130 mg/L at pH 4. Goethite retained up to 30.1 mg OC/g predominantly by ‘ligand exchange’; pyrophyllite sorbed maximally 12.5 mg OC/g, largely via ‘van der Waals forces’ and ‘Ca bridging’, while sorption of OM to vermiculite was 7.3 mg OC/g, mainly due to the formation of ‘Ca bridges’. Aromatic OM components were selectively sorbed by all minerals (goethite ≫ phyllosilicates). The sorption of OM was strongly hysteretic with the desorption into 0.01 M NaCl being larger for OM held by ‘Ca bridges’ and ‘van der Waals forces’ than by ‘ligand exchange’. Incubation experiments under aerobic conditions (initial pH 4; 90 days) revealed that OM mainly bound to minerals by ‘ligand exchange’ was more resistant against mineralization than OM held by non-columbic interactions (‘van der Waals forces’). Calcium bridges enhanced the stability of sorbed OM, especially for vermiculite, but less than the binding via ‘ligand exchange’. Combined evidence suggests that the extent and rate of mineralization of mineral-associated OM are governed by desorption. The intrinsic stability of sorbed OM as related to the presence of resistant, lignin-derived aromatic components appears less decisive for the sorptive stabilization of OM than the involved binding mechanisms. In a given environment, the type of minerals present and the solution chemistry determine the operating binding mechanisms, thereby the extent of OM sorption and desorption, and thus ultimately the bioavailability of mineral-associated OM.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 5
    Language: English
    In: Organic Geochemistry, 2004, Vol.35(3), pp.269-276
    Description: The dependence of dissolved organic carbon (DOC) retention on mineral phase properties is uncertain where soil solution pH is neutral. Therefore, ten soil and phyllosilicate clay fractions were used (after carbon oxidation) to investigate relationships between DOC retention at pH 7 and content of dithionite-extractable iron (Fe (sub d) ), specific surface area (SSA) and cation exchange capacity (CEC). DOC sorption sites were identified by blocking reactive hydroxyl groups with phosphate on subsamples. Reversibility of DOC sorption was determined by desorption experiments. Soil clay fractions sorbed about twice as much DOC as phyllosilicates. A positive relationship between DOC sorption and Fe (sub d) content suggests that this is due to pedogenic oxides in soil clays. Positive trends were also observed with SSA or CEC. Sorption of 9-44 mu g DOC m (super -2) indicates that DOC interacts only with fractions of the mineral surfaces. Phosphate treatment of subsamples reduced DOC sorption by 39-64% indicating a contribution of reactive hydroxyl groups as well as of siloxane surfaces of phyllosilicate clay minerals to DOC sorption. Desorption experiment removed 13-50% of sorbed DOC. Samples with and without phosphate treatment desorbed similar absolute amounts of DOC indicating that DOC associations with siloxane surfaces may be weaker than interactions with hydroxyl groups. Abstract Copyright (2004) Elsevier, B.V.
    Keywords: Dissolved Organic Carbon ; Sorption of Doc ; Mineral Surfaces ; Hydroxyl Groups ; Desorption of Doc ; Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2004, Vol.167(4), pp.439-448
    Description: In Saxony‐Anhalt, Germany, an area of about 6000 ha is covered by lignite‐ash‐derived substrates. In some cases, pollutants like heavy metals or toxic organic compounds had been disposed of together with the lignite ashes. For this reason, we assessed factors influencing the cation exchange capacity (CEC) of lignite‐ash substrates exposed to natural weathering. We chose four research sites reflecting the different methods of disposal: two dumped landfills and two lagooned ashes of different ages. After determining the CEC at pH 8.1 (CEC), we evaluated the influence of the content of silt and clay and the content of total organic C. As lignite‐ash‐derived substrates are rich in oxalate‐extractable Si, Al, and Fe, we performed an oxalate extraction and determined afterwards the CEC to assess the contribution of oxalate‐soluble compounds to the CEC. Moreover, we determined the variable charge of selected samples at pH values ranging from 4 to 7. The lignite‐ash‐derived soils had a high CEC with means ranging from 25.1 cmol kg to 88.8 cmol kg. The influence of the parent material was more important than the degree of weathering. The content of total organic C consisting of pedogenic organic matter and coked lignite particles together with the content of silt and clay played a statistically significant role in determining the CEC. Another property that influenced the amount of CEC in medium textured lignite ashes was the content of oxalate‐soluble silica and aluminum. After oxalate extraction, they lost about 30% of their CEC due to the dissolution of oxalate‐soluble compounds. In coarse textured lignite ashes, oxalate extraction led to higher amounts of CEC, probably due to an increase of surface area resulting either from the disintegration of particles or from etching caused by insufficient dissolution of magnetite and maghemite. Moreover, lignite‐ash‐derived substrates exhibit a high amount of pH‐dependent charge. The CEC decreased by 40% in a topsoil sample and by 51% in a subsoil sample as the pH declined from 7 to 4. Austauscheigenschaften von Böden aus Braunkohlenaschen In Sachsen‐Anhalt bedecken Substrate aus Braunkohlenaschen ca. 6000 ha der Landesfläche. Dabei wurden in einigen Fällen toxische Substanzen wie z. B. Schwermetalle oder organische Schadstoffe zusammen mit den Braunkohlenaschen ausgebracht. Da die Beweglichkeit von Schadstoffen u. a. von der Kationenaustauschbarkeit abhängt, wurden Untersuchungen an verwitterten Braunkohlenaschen durchgeführt, um Erkenntnisse über deren Austauscheigenschaften zu erhalten. Es wurden vier Flächen ausgewählt, welche die unterschiedlichen Verfahren zur Ablagerung der Aschen wiedergeben: zwei Kippdeponien und zwei Spüldeponien unterschiedlichen Alters. An Proben aus diesen Flächen bestimmten wir die potenzielle Kationenaustauschkapazität (KAK, gemessen bei pH 8.1) und überprüften den Zusammenhang von C und dem Gehalt an Schluff und Ton mit der KAK. Da Braunkohlenaschesubstrate große Mengen an oxalatlöslichem Si, Fe und Al enthalten, quantifizierten wir den Einfluss dieser Verbindungen auf die KAK durch eine Oxalat‐Extraktion mit anschließender Bestimmung der KAK an ausgewählten Proben. Darüber hinaus wurde die variable Ladung ausgewählter Proben bei pH‐Werten von 4 bis 7 bestimmt. Die Böden aus Braunkohlenaschen wiesen eine hohe KAK auf, deren Mittelwerte zwischen 25.1 cmol kg und 88.8 cmol kg lagen. Dabei konnte ein Einfluss des Ausgangsmaterials – nicht aber des Alters – auf die KAK festgestellt werden. Sowohl der Gehalt an C, bestehend aus pedogener organischer Substanz und verkokten Braunkohlenpartikeln, als auch die Menge an Schluff und Ton übten einen statistisch nachweisbaren Einfluss auf die KAK aus. Dabei war der durch C und die Menge an Schluff und Ton erklärbare Anteil der KAK bei den Kippdeponien höher als bei den Spüldeponien. Die Gegenwart oxalatlöslicher Bestandteile hatte große Auswirkungen auf die Höhe der KAK in der verspülten Asche mit mittlerer Textur. Nach einer Oxalat‐Extraktion verringerte sich die KAK um ca. 30 %. Dagegen stieg die KAK in Braunkohlenaschen mit hohen Anteilen an Sandfraktionen an, was wahrscheinlich durch eine Vergrößerung der reaktiven Oberfläche bedingt ist. Dies ist entweder durch den Zerfall einzelner großer Partikel in mehrere kleine oder durch eine unvollständige Lösung des in den Aschen vorkommenden Magnetits und Maghemits erklärbar. Die von uns untersuchten Braunkohlenaschen wiesen außerdem eine hohe variable Ladung auf. In einer Oberboden‐ und einer Unterbodenprobe war ein Rückgang der pH‐Werte von 7 auf 4 mit einem 51 %‐ bzw. 40 %igen Rückgang der KAK verbunden.
    Keywords: Lignite Ash ; Anthropic Soils ; Cation Exchange Capacity ; Oxalate Extractable Compounds ; Total Organic Carbon ; Variable Charge
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 7
    Language: English
    In: Biogeochemistry, 2006, Vol.77(1), pp.25-56
    Description: Soil organic matter (OM) can be stabilized against decomposition by association with minerals, by its inherent recalcitrance and by occlusion in aggregates. However, the relative contribution of these factors to OM stabilization is yet unknown. We analyzed pool size and isotopic composition ( 14 C, 13 C) of mineral-protected and recalcitrant OM in 12 subsurface horizons from 10 acidic forest soils. The results were related to properties of the mineral phase and to OM composition as revealed by CPMAS 13 C-NMR and CuO oxidation. Stable OM was defined as that material which survived treatment of soils with 6 wt% sodium hypochlorite (NaOCl). Mineral-protected OM was extracted by subsequent dissolution of minerals by 10% hydrofluoric acid (HF). Organic matter resistant against NaOCl and insoluble in HF was considered as recalcitrant OM. Hypochlorite removed primarily 14 C-modern OM. Of the stable organic carbon (OC), amounting to 2.4–20.6 g kg −1 soil, mineral dissolution released on average 73%. Poorly crystalline Fe and Al phases (Fe o , Al o ) and crystalline Fe oxides (Fe d−o ) explained 86% of the variability of mineral-protected OC. Atomic C p /(Fe+Al) p ratios of 1.3–6.5 suggest that a portion of stable OM was associated with polymeric Fe and Al species. Recalcitrant OC (0.4–6.5 g kg −1 soil) contributed on average 27% to stable OC and the amount was not correlated with any mineralogical property. Recalcitrant OC had lower Δ 14 C and δ 13 C values than mineral-protected OC and was mainly composed of aliphatic (56%) and O-alkyl (13%) C moieties. Lignin phenols were only present in small amounts in either mineral-protected or recalcitrant OM (mean 4.3 and 0.2 g kg −1 OC). The results confirm that stabilization of OM by interaction with poorly crystalline minerals and polymeric metal species is the most important mechanism for preservation of OM in these acid subsoil horizons.
    Keywords: C isotopes ; Hydrofluoric acid ; Lignin ; Recalcitrant organic matter ; Sodium hypochlorite ; Stable organic matter
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, 13 October 2003, Vol.166(5), pp.642-648
    Description: To obtain information on regional soil carbon (C) stocks, we prepared a soil C inventory for the central German State Saxony‐Anhalt. We used the State Soil Database SABO_P (achsen‐nhalt den_rofildatenbank), which contains data from 3,600 soil profiles with 16,300 individual soil horizons and combined it with a geographic information system (GIS ArcView). Soil C stocks down to a depth of 100 cm were compiled for the three major soil regions of Saxony‐Anhalt (soil region 2: river valleys and floodplains; soil region 4: pre‐Weichselian moraines, and soil region 6: loess‐covered areas), which represent 83 % of the total state territory. The three major soil regions in Saxony‐Anhalt comprise on average 12.7 (soil region 2), 8.9 (soil region 4), and 12.8 kg C m (soil region 6). Total C content of the area investigated was 191 tg. The typical soils of the region, Haplic Chernozems, contain on average 13.9 kg C m. With few exceptions, soil C did not vary significantly within identical taxonomic groups among different soil subregions. However, Chernozems of soil subregion 3 (Wanzlebener Löß‐Plateau; 19.8 kg C m) contain significantly more C than the Chernozems of soil subregions 9 (Pollebener, Gerbstedter and Lettewitzer Löß‐Plateau; 12.1 kg C m) and 15 (Barnstädter Löß‐Plateau 12.2 kg C m). The spatial distribution of C stocks in Saxony‐Anhalt was represented in a map which suggests the existence of a strong link between the geomorphologic position of a given soil and its capacity to store organic C. Within the same taxonomic unit, finer textured soils stored more carbon than coarse‐textured ones. Inventur der Vorräte an organischem Kohlenstoff für Böden von Sachsen‐Anhalt mittels GIS und basierend auf der Bodenprofildatenbank SABO_P Wir ermittelten die räumliche Verbreitung der Kohlenstoffvorräte in den Böden Sachsen‐Anhalts. Dazu wurde die Datenbank SABO_P (achsen‐nhalt den‐rofildatenbank), die Daten von insgesamt 3.600 Profilen mit zusammen 16.300 Horizonten enthält, mit einem Geographischen Informationssystem (GIS, ArcView) gekoppelt. Wir schätzten die Kohlenstoffvorräte bis 100 cm Bodentiefe für die drei wichtigsten Bodenregionen in Sachsen‐Anhalt (Bodenregion 2: Flusslandschaften; Bodenregion 4: Altmoränenlandschaften; Bodenregion 6: Löss‐ und Sandlösslandschaften), die 83 % der Landesfläche umfassen. Die durchschnittlichen Gehalte an organischem Kohlenstoff in den drei Bodenregionen sind 12,7 kg C m (Bodenregion 2), 8,9 kg C m (Bodenregion 4) und 12,8 (Bodenregion 6). Zusammen enthalten die drei Bodenregionen 191 tg organischen Kohlenstoff. Die typischen Schwarzerden Sachsen‐Anhalts (Norm‐Tschernoseme) enthalten durchschnittlich 13,9 kg C m. Innerhalb der gleichen taxonomischen Einheit waren die Kohlenstoffgehalte zwischen einzelnen Bodenlandschaften mit sehr wenigen Ausnahmen gleich. Eines der wenigen Beispiele für signifikant unterschiedliche Kohlenstoffspeicherung sind die Schwarzerden der Bodenlandschaften 3 (Wanzlebener Löss‐Plateau; 19,8 kg C m), die damit deutlich über den Werten für die Schwarzerden der Bodenlandschaften 9 (Pollebener, Gerbstedter und Lettewitzer Löss‐Plateau; 12,1 kg C m) und 15 (Barnstädter Löss‐Plateau; 12,2 kg C m) liegen. Die räumliche Verteilung der Gehalte an organischem Kohlenstoff in den Böden Sachsen‐Anhalts wurde in einer Karte dargestellt. Die Karte zeigt, dass in Sachsen‐Anhalt ein funktioneller Zusammenhang zwischen geomorphologischer Position und der Fähigkeit der Böden, organischen Kohlenstoff zu speichern, existiert. Innerhalb der gleichen taxonomischen Einheit speichern Böden mit feiner Textur mehr Kohlenstoff als solche mit grober Textur.
    Keywords: Organic Carbon ; Soil Carbon Inventory ; Carbon Storage ; Regional Carbon Budget ; Gis ; Soil Data Base Sabo_P
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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