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  • 1
    Language: English
    In: Plant and Soil, 2010, Vol.330(1), pp.481-501
    Description: A modelling approach was used to extend the knowledge about the processes that affect the availability of the nutrient P and the toxic agent As V in the rhizosphere in the presence of a strong sorbent. Based on compartment system experiments in which Zea mays was grown the following hypothesis were assumed: a) measured P concentration gradients can be explained by the mobilisation of P by the root exudate citrate, and b) measured As V concentration gradients can be explained by the simultaneous effect of the competitive sorption of As V and P and the competitive uptake of As V and P. First, the feasibility of the applied description of soil chemical processes was justified. Then competitive uptake was implemented in the computer code using two different mathematical approaches. Our model calculation provided support for hypothesis a) and suggested that hypothesis b) has to be extended. The results show that the competitive uptake of As V and P has an influence on As V concentrations in the rhizosphere, but including competitive uptake was not sufficient to predict observed As V concentration profiles. Recent results on plant As-metabolism like As III efflux and Si As III interaction probably have to be included in addition for simulation of measured As V concentration profiles.
    Keywords: Rhizosphere ; Modelling ; Speciation ; Phosphate ; Arsenate ; Goethite
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Language: English
    In: Plant and Soil, 2013, Vol.371(1), pp.267-279
    Keywords: Exchangeable K ; Non-exchangeable K ; Subsoil ; Illite ; Soil solution ; Ca
    ISSN: 0032-079X
    E-ISSN: 1573-5036
    Source: Springer Science & Business Media B.V.
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  • 3
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 August 2018, Vol.235, pp.89-102
    Description: Ferric iron (Fe ) solid phases serve many functions in soils and sediments, which include providing sorption sites for soil organic matter, nutrients, and pollutants. The reactivity of Fe solid phases depends on the mineral structure, including the overall crystallinity. In redox-active soils and sediments, repeated reductive dissolution with subsequent exposure to aqueous ferrous iron (Fe ) and oxidative re-precipitation can alter Fe phase crystallinity and reactivity. However, the trajectory of Fe mineral transformation under redox fluctuations is unclear and has been reported to result in both increases and decreases in Fe phase crystallinity. Several factors such as water budget, organic matter input, redox dynamics as well as the initial Fe phase composition might play a role. The objective of our study was to examine if Fe minerals in soils that differ in porosity-dependent water leaching rate and initial Fe phase crystallinity, demonstrate distinct mineral transformations when subjected to redox fluctuations. We sampled paired plots of two soil types under similar management but with different water leaching rates and contrasting Fe oxide crystallinity — an Alisol rich in crystalline Fe phases and an Andosol rich in short-range-ordered (SRO) Fe phases. The two soils were either exposed to several decades of redox fluctuations during rice paddy cultivation (paddy) or to predominantly oxic conditions in neighboring vegetable gardens (non-paddy). Paddy soils are uniquely suited for this type of study because they are regularly submerged and develop regular redox fluctuations. We also incubated the non-paddy soils in the laboratory for one year through eight anoxic/oxic cycles and monitored the aqueous soil geochemistry. Mössbauer spectroscopy was then used to evaluate Fe mineral speciation in field soils (paddy and non-paddy) and laboratory incubations. In the field soils, we found that redox fluctuation had contrasting effects on Fe oxide crystallinity, with crystallinity being lower in the Alisol paddy soil and higher in the Andosol paddy soil than in their corresponding non-paddy controls. In the laboratory incubation experiment, Eh, pH and dissolved Fe responded as anticipated, with elevated Fe concentrations during the anoxic periods as well as low Eh and high pH. Mössbauer measurements suggest the fluctuating redox incubation was beginning to alter Fe oxide crystallinity along the same trajectory as observed in the field, but the changes were within the range of fitting errors. We propose that reductive dissolution of crystalline Fe oxides prevails in the soil rich in crystalline Fe oxides (Alisol) and that re-precipitation as SRO Fe oxides is favored by constrained leaching, which leads to the observed decrease in Fe oxide crystallinity. In the soil rich in SRO Fe phases (Andosol), preferential reductive dissolution of SRO Fe oxides coupled with stronger leaching of dissolved Fe causes the observed relative increase in crystallinity of the remaining Fe oxides. The observed increase in Fe oxide crystallinity may further be a result of Fe(II)-catalyzed re-crystallization of SRO Fe oxides. These findings indicate that, besides other factors, the Fe mineral composition of the initial soil or sediment as well as the leaching rate likely influence the trajectory of Fe oxide evolution under alternating redox-conditions.
    Keywords: Fe Oxides ; Redox Fluctuation ; Paddy Soils ; Mössbauer Spectroscopy ; Alisol ; Andosol ; Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 4
    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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  • 5
    Language: English
    In: Plant and Soil, 2004, Vol.258(1), pp.307-327
    Description: Soil solution composition changes with time and distance from the root surface as a result of mass flow, diffusion, plant nutrient uptake and root exudation. A model system was designed, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). K + concentration in the rhizosphere soil solution decreased during the initial growth stage (12 days after planting, DAP). Thereafter K + accumulated with time, due to mass flow as the dominating process. The extend of K + accumulation depended on the initial fertiliser application. As K + concentrations in soil solution increase, not only as a result of transport exceeding uptake, but also as a result of decreasing soil water content, it is hypothesised that K concentration in soil solution is not the only trigger for the activity of K transporters in membranes, but ABA accumulation in roots induced by decreasing soil matric potentials may add to the regulation. A strong decrease of rhizosphere pH with time is observed as a result of H + efflux from the roots in order to maintain cation-anion balance. In addition the K + to Ca 2+ ratio was altered continuously during the growing period, which has an impact on Ca 2+ uptake and thus firmness of cell walls, apoplast pH, membrane integrity and activity of membrane transporters. The value of osmotic potential in the rhizosphere soil solution increased with time indicating decreasing soil water availability. Modelling approaches based on the data obtained with the system might help to fill in the time gaps caused by the low temporal resolution of soil solution sampling method.
    Keywords: K ; matric potential ; osmotic potential ; pH ; rhizosphere ; soil solution
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 6
    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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  • 7
    Language: English
    In: Environmental Pollution, 2009, Vol.157(11), pp.3016-3024
    Description: is known to hyperaccumulate As but the mechanism is poorly understood. We found an increase of As concentration with increasing soil solution As concentrations, but P application had no impact, although plant P concentrations responded to different rates of P supply. As in fronds was dominantly (82–89%) present in the form of AsIII. In roots we detected 45% as AsIII which is higher than reported in previous studies and supports substantial As-reduction to take place in roots. We detected PC2/3GS–AsIII, PC2–GS–AsIII and (PC2)2–AsIII in increasing amounts with application of As. The total amount of PC was in the range reported previously and far too small to assign a significant role in As detoxification to PCs. The close correlation between S and As in fronds and the lack of data on sulphur uptake and metabolism indicates the need for a detailed investigation on sulphur nutritional status and As metabolism in . As–PC complexes were detected in increasing amounts with increasing As availability, but total amounts were small and do not explain the close correlation between S and As in fronds.
    Keywords: Arsenic Detoxification ; Arsenic Speciation ; Hyperaccumulator ; PC–As Complexes ; P Uptake ; Sulphur Metabolism ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 8
    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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  • 9
    Language: English
    In: Geoderma, 2010, Vol.157(1), pp.1-14
    Description: Paddy soils make up the largest anthropogenic wetlands on earth. They may originate from any type of soil in pedological terms, but are highly modified by anthropogenic activities. The formation of these Anthrosols is induced by tilling the wet soil (puddling), and the flooding and drainage regime associated with the development of a plough pan and specific redoximorphic features. Redox potential oscillations due to paddy management control microbial community structure and function and thus short-term biogeochemical processes. After flooding, microbial reduction processes sequentially use NO , Mn , Fe , SO as electron acceptors, accompanied by the emission of the trace gases N O, N , H S, CH and — due to reduction-induced increasing pH — NH . This results in N losses and low N fertilizer use efficiency. However, transport of atmospheric O to the roots via the rice plant's aerenchyma modifies conditions in the rhizosphere, leading to nitrification and methane oxidation, and precipitation of Mn and Fe oxides. High concentrations and fluxes of dissolved organic matter (DOM) in paddy soils from plant debris trigger microbial activity and thus the emission of greenhouse gases. Retention of DOM by soil minerals and its subsequent stabilisation against microbial decay depend on the redox state (e.g. DOM precipitation by Fe under anaerobic conditions). Oscillation in redox conditions may enhance retention and stabilisation of DOM by Fe oxyhydroxides. Induced by the periodic short-term redox cycles, paddy management over long periods has strong effects on long-term biogeochemical processes. Frequent irrigation intensifies mineral weathering and leaching processes. High concentrations of DOM during flooding seasons enhance the changes and the release of structural iron in clay minerals, and support the formation of ferrihydrite. Repeated redox alternations lead to a translocation of iron in various directions, and particularly increase the crystallinity of iron oxides. This results also in higher total iron oxide contents in paddy compared to non-paddy soils. The large accumulation of soil organic matter (SOM) observed in some, but not all paddy soils, is considered to be due to high input of plant residues and charred material associated with retarded decomposition under anaerobic conditions. There is also evidence of SOM stabilisation via occlusion into aggregates and phytoliths as well as interactions with clay minerals and iron oxides. SOM accumulation in paddy subsoils can be explained by downward movement of DOM and its stabilisation by interaction with iron oxides. A specific feature of paddy soils is the coupling of organic matter turnover with mineral transformations and fluxes, which seem to be intensified by the alternating redox conditions with increasing age of paddy soil development. Bioavailability of soil organic N is strongly coupled to SOM cycling and is a crucial parameter determining crop yield. Anaerobic conditions inhibit N mineralization, with a high risk of gaseous N losses. In paddy soils the management-induced, microbially mediated redox processes control the dynamics of soil minerals and soil organic matter, which are strongly related to the microbial accessibility of C and N, but also of Fe.
    Keywords: Anthrosols ; Wetland ; Paddy Management ; Mineral Transformation ; Soil Organic Matter ; Soil N ; Soil Solution Chemistry ; Microbial Community ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Geoderma, 2008, Vol.147(3), pp.141-150
    Description: Hydrotalcite, a Mg–Al layered double hydroxide [Mg Al (OH) ] [CO ] · 4H O, occurs in alkaline soils, especially when affected by industrial waste input. It strongly interacts with anionic compounds, thus can contribute to the accumulation and storage of organic matter in such soils. We studied the sorption of organic matter (OM) to hydrotalcite with different nitrate to carbonate ratios in the interlayer. A range of solutions with different concentrations of organic carbon (OC) was prepared to test the hydrotalcites' affinity for OM. In order to identify sorption mechanisms, we analyzed hydrotalcites before and after sorption of OM by X-ray diffraction and determined specific surface area (SSA) and pore volume. Spectroscopic and colorimetric methods were applied to track changes in the OM composition, resulting from preferential sorption of organic fractions. Hydrotalcite sorbed large amounts of natural dissolved OM (up to 135.2 ± 20.5 mg organic C g ) under chemical solution conditions comparable with those in calcareous alkaline soils. The interlayer carbonate-to-nitrate ratio affected the OM sorption under highly alkaline conditions (pH ≥ 9) but not under neutral to weakly alkaline conditions (pH 7–8). We assume the higher the portion of carbonate as charge balancing anion the lower is the mineral's surface charge. Enhanced deprotonation of surface hydroxyl groups at high solution pH (pH ≥ 9) would therefore reduce the surface charge, thus causing decreasing electrostatic attraction of organic anions. Hydrotalcite preferentially retained aromatic compounds. Sorption of OM to hydrotalcite takes place solely at external surface sites, predominately by ligand exchange for surface hydroxyl groups.
    Keywords: Layered Double Hydroxides ; Preferential Sorption ; Organic Matter ; Ligand Exchange ; Aromatic Compounds ; Specific Surface Area (SSA) ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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