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Berlin Brandenburg

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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Language: English
    In: Biogeochemistry, 2019, Vol.143(1), pp.31-54
    Description: Submerged rice cultivation is characterized by redox fluctuations and results in the formation of paddy soils, often accompanied by soil organic carbon (SOC) accumulation. The impact of redox fluctuations and the underlying soil type on the fate of organic carbon (OC) in paddy soils are unknown. Hence, we mimicked paddy soil development in the laboratory by exposing two soil types with contrasting mineral assemblages (Alisol and Andosol) to eight anoxic–oxic cycles over 1 year. Soils regularly received 13 C-labeled rice straw. As control we used a second set of samples without straw addition as well as samples under static oxic conditions with and without straw. Headspaces were analyzed for carbon dioxide and methane as well as their δ 13 C signatures, whereas soil solutions were analyzed for redox potential, pH, dissolved iron, and dissolved organic carbon (DOC and DO 13 C). At the end of the experiment, when eight redox cycles were completed, mineral-associated organic matter (MOM) was isolated by density fractionation and characterized for δ 13 C, non-cellulosic carbohydrates, and lignin-derived phenols. Moreover, changes in the soil’s microbial community structure were measured. For both soil types, headspace data confirmed less respiration in straw-amended soils with redox fluctuation than in those under static oxic conditions. The δ 13 C data revealed that, irrespective of soil type, straw carbon allocation into MOM was larger in soils with redox fluctuation than in those with static oxic conditions. A net increase in MOM after the one-year incubation, however, was only observed in the respective Andosol, probably due to abundant reactive minerals capable of OC uptake. In the Alisol, straw OC most likely exchanged initial MOM. A potential for lignin accumulation in the MOM of soils incubated with straw and redox fluctuation was observed for both soil types. Lignin and carbohydrates suggest a plant origin of MOM formed under redox fluctuation. The initially similar bacterial community composition of the Alisol and Andosol changed differently under redox fluctuation. The stronger change in the Alisol indicates less protective microbial habitats. In summary, the overall turnover of straw OC in soils under redox fluctuation seems to be independent of soil type, while net accumulation of SOC as well as the evolution of the bacterial community structure may in part depend on soil type, suggesting an impact of the soil’s mineral composition.
    Keywords: Microbial community ; Mineral-associated organic matter ; Mineralization ; Paddy soils ; Redox fluctuation ; Soil organic matter formation
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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