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  • Journal of Plant Nutrition and Soil Science
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  • 1
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2013, Vol.176(4), pp.509-519
    Description: Dolomite (CaMg(CO)) constitutes half of the global carbonates. Thus, many calcareous soils have been developing rather from dolomitic rocks than from calcite (CaCO)‐dominated limestone. We developed a physical fractionation procedure based on three fractionation steps, using sonication with subsequent density fractionation to separate soil organic matter (SOM) from dolomite‐derived soil constituents. The method avoids acidic pretreatment for destruction of carbonates but aims at separating out carbonate minerals according to density. The fractionation was tested on three soils developed on dolostone parent material (alluvial gravel and solid rock), differing in organic‐C (OC) and inorganic‐C (IC) concentrations and degree of carbonate weathering. Soil samples were suspended and centrifuged in Na‐polytungstate (SPT) solutions of increasing density, resulting in five different fractions: two light fractions 20 μm and 2.6 g cm) was dominated by dolomite (85%–95%). The density separation yielded fractions differing in mineral compositions, as well as in SOM, indicated by soil‐type‐specific OC distributions and decreasing OC : N ratios with increasing density of fractions. The presented method is applicable to a wide range of dolomitic and most likely to all other calcareous soils.
    Keywords: Carbonates ; Sodium Polytungstate ; Carbon ; Iron Oxides ; Sonication
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 2
    Language: English
    In: Journal of Plant Nutrition and Soil Science, February 2008, Vol.171(1), pp.52-60
    Description: Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant‐derived carbohydrates seem easily degradable. Carbohydrates and N‐rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co‐)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from 90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co‐)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM‐derived soil C ranges from 20 to 55 Mg ha in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co‐)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM‐derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co‐)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co‐)precipitation with Al and Fe to DOM retention.
    Keywords: Biodegradation ; Chemical Composition ; Co‐Precipitation ; Dissolved Organic Matter ; Dom ; Forest Soils ; Sorption
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, December 2018, Vol.181(6), pp.894-904
    Description: Sonication is widely used for disruption of suspended soil aggregates. Calorimetric calibration allows for determining sonication power and applied energy as a measure for aggregate disrupting forces. Yet other properties of sonication devices (., oscillation frequency and amplitude, sonotrode diameter) as well as procedure details (soil‐to‐water ratio, size, shape, and volume of used containers) may influence the extent of aggregate disruption in addition to the applied energy. In this study, we tested potential bias in aggregate disruption when different devices or procedures are used in laboratory routines. In nine laboratories, three reference soil samples were sonicated at 30 J mL and 400 J mL. Aggregate disruption was estimated based on particle size distribution before and after sonication. Size distribution was obtained by standardized submerged sieving for particle size classes 2000–200 and 200–63 µm, and by dynamic imaging for particles 45 W). Thus, these sonication device properties need to be listed when reporting on sonication‐based soil aggregate disruption. The overall small differences in the degree of disruption of soil aggregates between different laboratories demonstrate that sonication with the energies tested (30 and 400 J mL) provides replicable results despite the variations regarding procedures and equipment.
    Keywords: Disaggregation ; Particle Size Fractions ; Reproducibility ; Round‐Robin Test ; Ultrasound
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2016, Vol.179(2), pp.129-135
    Description: Phosphorus is one of the major limiting factors of primary productivity in terrestrial ecosystems and, thus, the P demand of plants might be among the most important drivers of soil and ecosystem development. The P cycling in forest ecosystems seems an ideal example to illustrate the concept of ecosystem nutrition. Ecosystem nutrition combines and extents the traditional concepts of nutrient cycling and ecosystem ecology. The major extension is to consider also the loading and unloading of nutrient cycles and the impact of nutrient acquiring and recycling processes on overall ecosystem properties. Ecosystem nutrition aims to integrate nutrient related aspects at different scales and in different ecosystem compartments including all processes, interactions and feedbacks associated with the nutrition of an ecosystem. We review numerous previous studies dealing with P nutrition from this ecosystem nutrition perspective. The available information contributes to the description of basic ecosystem characteristics such as emergence, hierarchy, and robustness. In result, we were able to refine Odum's hypothesis on P nutrition strategies along ecosystem succession to substrate related ecosystem nutrition and development. We hypothesize that at sites rich in mineral‐bound P, plant and microbial communities tend to introduce P from primary minerals into the biogeochemical P cycle (acquiring systems), and hence the tightness of the P cycle is of minor relevance for ecosystem functioning. In contrast, tight P recycling is a crucial emergent property of forest ecosystems established at sites poor in mineral bound P (recycling systems). We conclude that the integration of knowledge on nutrient cycling, soil science, and ecosystem ecology into holistic ecosystem nutrition will provide an entirely new view on soil–plant–microbe interactions.
    Keywords: Ecosystem Properties ; P Recycling ; P Nutrition Strategy ; Forest Nutrition ; P Acquiring
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 5
    Language: English
    In: Journal of Plant Nutrition and Soil Science, February 2001, Vol.164(1), pp.57-64
    Description: There is an urgent need to improve the methods to estimate solute fluxes in soil, e.g. cumulative capture of leaching ions by exchange resin cores. We compared the suitability of different resin materials, core sizes, and installation procedures to assess nutrient leaching in a highly permeable, tropical Xanthic Ferralsol. Three different cation and anion resins, respectively, and two combined anion‐cation resins were tested in laboratory experiments with respect to their removal and recovery of nutrients (Mg, NH, NO) and total dissolved organic carbon (TOC) from solution. In a field experiment, cores with three different diameters (25, 100, and 200 mm) were installed either vertically from the soil surface or laterally from a soil pit. Cumulative leaching of NO and NH and of applied Sr was determined after 45 days. The combined anion and cation exchange resin (MB 20) showed satisfactory recovery of NO and NH from solution. None of the investigated resins could be used for TOC removal from solution due to high contents of soluble carbon compounds in the resins. Wetting and drying cycles did not affect the removal of solutes from solution or subsequent recovery from the MB 20 resin. Additionally, the combined resin MB 20 was easier to handle than separate anion or cation resins and was therefore used for further field experimentation. The smallest core size (25 mm) was not suitable for nutrient leaching determination due to high preferential flow along the inner core walls. The medium diameter cores (100 mm) showed the lowest variability and the best correlation between NO and Sr capture. They were easier to install and retrieve than the large diameter cores (200 mm), which posed serious handling problems and soil disturbance. The lateral installation caused significantly lower artificial flow in comparison to a vertical installation, which was shown by the lower Sr loss and slightly lower N capture. Therefore, a lateral installation of medium sized resin cores (100 mm diameter) from a soil pit was superior to the other alternatives tested in this study. Abschätzung des Nährstoffaustrages aus stark durchlässigen tropischen Böden mit Austauscherharz‐Zylindern Es gibt einen dringenden Bedarf zur Weiterentwicklung von Methoden, mit denen Stoffflüsse im Boden abgeschätzt werden können, wie z.B. mit Austauscherharz‐Zylindern („exchange resin cores“). Diese Studie befasst sich mit der Eignung verschiedener Austauscherharze zur Bestimmung von kumulativen Nährstoffausträgen aus einem stark durchlässigen tropischen Xanthic Ferralsol. Neben den Sorptionseigenschaften von Anionen‐ und Kationenharzen sowie kombinierten Anionen‐Kationenharzen für Nährstoffe (Mg, NH, NO) und gelösten organischen Kohlenstoff (TOC) wurden mögliche Durchmesser und zwei verschiedene Techniken zum Einbau der Zylinder in Böden untersucht. In einer Feldstudie wurden Harzzylinder dreier Durchmesser (25, 100 und 200 mm) entweder vertikal von der Bodenoberfläche aus oder lateral von einer Grube aus eingebaut. Die Auswaschung von NO und NH sowie von ausgebrachtem Sr wurde nach 45 Tagen bestimmt. Das kombinierte Anionen‐Kationenharz (Amberlite MB 20) zeigte gute Sorptionseigenschaften für NO und NH. Aufgrund hoher Gehalte an löslichen organischen Substanzen im Harzmaterial war keines der Harze zur Erfassung von TOC geeignet. Wiederholte Trocknungs‐ und Befeuchtungszyklen hatten keinen Einfluss auf die Adsorptionseigenschaften des MB 20 Harzes. Wegen der zusätzlich leichteren Handhabbarkeit eines kombinierten Harzes wurde das MB 20 für die anschließenden Feldversuche eingesetzt. Die Harzzylinder mit dem kleinsten Durchmesser (25 mm) waren wegen starker Stoffflüsse entlang der inneren Wandung der Zylinder nicht zur Bestimmung der Nährstoffauswaschung geeignet. Die Harzzylinder mit mittlerem Durchmesser (100 mm) wiesen die geringste Variabilität zwischen den Einzelmessungen auf und waren einfacher zu installieren und auszubauen als die großen Zylinder (200 mm). Ein lateraler Einbau verursachte eine signifikant geringere Bodenstörung als ein vertikaler Einbau von oben, wie die geringere Sr‐ und N‐Auswaschung bewies. Lateraler Einbau der Harzzylinder mit mittlerem Durchmesser (100 mm) zeigte sich gegenüber den anderen getesteten Varianten überlegen.
    Keywords: Exchange Resin ; Nitrogen ; Nutrient Leaching ; Total Dissolved Organic Carbon ; Strontium
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2000, Vol.163(5), pp.531-535
    Description: The retention of dissolved organic matter in soils is mainly attributed to interactions with the clay fraction. Yet, it is unclear to which extent certain clay‐sized soil constituents contribute to the sorption of dissolved organic matter. In order to identify the mineral constituents controlling the sorption of dissolved organic matter, we carried out experiments on bulk samples and differently pretreated clay‐size separates (untreated, organic matter oxidation with HO, and organic matter oxidation with HO + extraction of Al and Fe oxides) from subsoil horizons of four Inceptisols and one Alfisol. The untreated clay separates of the subsoils sorbed 85 to 95% of the dissolved organic matter the whole soil sorbed. The sorption of the clay fraction increased when indigenous organic matter was oxidized by HO. Subsequent extraction of Al and Fe oxides/hydroxides caused a sharp decrease of the sorption of dissolved organic matter. This indicated that these oxides/hydroxides in the clay fraction were the main sorbents of dissolved organic matter of the investigated soils. Moreover, the coverage of these sorbents with organic matter reduced the amount of binding sites available for further sorption. The non‐expandable layer silicates, which dominated the investigated clay fractions, exhibited a weak sorption of dissolved organic matter. Whole soils and untreated clay fractions favored the sorption of ”︁hydrophobic” dissolved organic matter. The removal of oxides/hydroxides reduced the sorption of the lignin‐derived ”︁hydrophobic” dissolved organic matter onto the remaining layer silicates stronger than that of ”︁hydrophilic” dissolved organic matter. Sorption gelöster organischer Substanz an mineralische Bestandteile der Tonfraktion von Unterbodenhorizonten Bindung an die Tonfraktion gilt als Hauptursache für den Rückgang der Gehalte an gelöster organischer Substanz in der Bodenlösung während deren Passage des Solums. Unklar ist allerdings, welchen Beitrag verschiedene Mineralbestandteile der Tonfraktion zur Sorption gelöster organischer Substanz leisten. Wir haben deshalb die Sorption gelöster organischer Substanz an Gesamtproben und unterschiedlich behandelten Proben der Tonfraktion (unbehandelt, nach Oxidation organischer Substanz mittels HO, nach Oxidation organischer Substanz + Extraktion pedogener Oxide) von Unterbodenhorizonten zweier Braunerden, zweier Pseudogleye und einer Parabraunerde untersucht. Die unbehandelte Tonfraktion war für 85 bis 95% der Sorption gelöster organischer Substanz der Gesamtböden verantwortlich. Oxidation der organischen Substanz in der Tonfraktion ließ die Sorption von gelöster organischer Substanz ansteigen. Die darauf folgende Extraktion pedogener Oxide hingegen verringerte die Sorption deutlich. Dies lässt vermuten, dass Oxide der Tonfraktion die wesentlichen Sorbenten für gelöste organische Substanz in Böden sind und dass ihre Belegung mit organischer Substanz die Sorption gelöster organischer Substanz erschwert. Die nicht quellfähigen Schichtsilikate, die die untersuchten Tonfraktionen dominierten, zeigten dagegen nur eine sehr geringe Bindung gelöster organischer Substanz. Gesamtböden wie auch die unbehandelten Tonfraktionen sorbierten bevorzugt „hydrophobe“ organische Substanz. Entfernen der Oxide verminderte die Sorption ligninbürtiger „hydrophober“ gelöster organischer Substanz an die verbliebenen Schichtsilikate stärker als die Sorption „hydrophiler“ gelöster organischer Substanz.
    Keywords: Dissolved Organic Matter ; Soil Clay Fraction ; Clay Minerals ; Sesquioxides
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 7
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2016, Vol.179(4), pp.425-438
    Description: Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m a, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.
    Keywords: Forest Ecosystem ; Phosphorus ; Fluxes ; Soil ; Processes ; Hydrology
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2005, Vol.168(5), pp.649-659
    Description: Dissolved organic matter (DOM) is important for the cycling and transport of carbon (C) and nitrogen (N) in soil. In temperate forest soils, dissolved organic N (DON) partly escapes mineralization and is mobile, promoting loss of N leaching. Little information is available comparing DOC and DON dynamics under tropical conditions. Here, mineralization is more rapid, and the demand of the vegetation for nutrients is larger, thus, leaching of DON could be small. We studied concentrations of DOC and DON during the rainy seasons 1998–2001 in precipitation, canopy throughfall, pore water in the mineral soil at 5, 15, 30, and 80 cm depth, and stream water under different land‐use systems representative of the highlands of northern Thailand. In addition, we determined the distribution of organic C (OC) and N (ON) between two operationally defined fractions of DOM. Samples were collected in small water catchments including a cultivated cabbage field, a pine plantation, a secondary forest, and a primary forest. The mean concentrations of DOC and DON in bulk precipitation were 1.7 ± 0.2 and 0.2 ± 0.1 mg L, respectively, dominated by the hydrophilic fraction. The throughfall of the three forest sites became enriched up to three times in DOC in the hydrophobic fraction, but not in DON. Maximum concentrations of DOC and DON (7.9–13.9 mg C L and 0.9–1.2 mg N L, respectively) were found in samples from lysimeters at 5 cm soil depth. Hydrophobic OC and hydrophilic ON compounds were released from the O layer and the upper mineral soil. Concentrations of OC and ON in mineral‐soil solutions under the cabbage cultivation were elevated when compared with those under the forests. Similar to most temperate soils, the concentrations in the soil solution decreased with soil depth. The reduction of OC with depth was mainly due to the decrease of hydrophobic compounds. The changes in OC indicated the release of hydrophobic compounds poor in N in the forest canopy and the organic layers. These substances were removed from solution during passage through the mineral soil. In contrast, organic N related more to labile microbial‐derived hydrophilic compounds. At least at the cabbage‐cultivation site, mineralization seemed to contribute largely to the decrease of DOC and DON with depth, possibly because of increased microbial activity stimulated by the inorganic‐N fertilization. Similar concentrations and compositions of OC and ON in subsoils and streams draining the forested catchments suggest soil control on stream DOM. The contribution of DON to total dissolved N in those streams ranged between 50% and 73%, underscoring the importance of DOM for the leaching of nutrients from forested areas. In summary, OC and ON showed differences in their dynamics in forest as well as in agricultural ecosystems. This was mainly due to the differing distribution of OC and ON between the more immobile hydrophobic and the more easily degradable hydrophilic fraction. Gelöster organischer Kohlenstoff und Stickstoff in Freiland‐ und Bestandesniederschlag, der Bodenlösung sowie in primären Vorflutern in der tropischen Bergregion Nord‐Thailands Gelöste organische Substanz (DOM) spielt eine entscheidende Rolle beim C‐ und N‐Kreislauf und ‐transport im Boden. In Waldböden der gemäßigten Zonen scheint gelöster organischer N (DON) die mobilste N‐Bindungsform darzustellen. Auch im Vergleich zum DOC ist DON leichter verlagerbar. Nur wenig ist jedoch über die DOC‐ und DON‐Dynamik unter tropischen Bedingungen bekannt. In dieser Studie wurden während der Regenzeiten 1998–2001 die DOC‐ bzw. DON‐Konzentrationen in Niederschlag, Bestandesniederschlag, Bodenlösung in 5, 15, 30 und 80 cm Tiefe und Abfluss kleiner Wassereinzugsgebiete in repräsentativen Landnutzungsformen des tropischen Berglands Nordthailands untersucht. Zusätzlich wurde die Verteilung von DOC und DON in zwei operational definierten DOM‐Fraktionen bestimmt. Proben wurden auf einer Ackerfläche (Kohlanbau), in einer Kiefernaufforstung, einem Sekundärwald und einem Primärwald genommen. Die mittleren DOC‐ und DON‐Konzentrationen betrugen im Niederschlag 1.7 ± 0.2 bzw. 0.2 ± 0.1 mg L, wobei die hydrophile Fraktion dominierte. Der Bestandesniederschlag wies bis zu dreifach höhere DOC‐Konzentrationen auf, vornehmlich in der hydrophoben Fraktion. Stickstoff ließ dagegen keine Anreicherung erkennen. Die maximalen Konzentrationen (7.5–13.9 mg C L und 0.9–1.2 mg N L) wurden in den Lysimeterproben aus 5 cm Bodentiefe gemessen. Die Freisetzung in den Auflagen und im obersten Mineralboden erfolgte bei C größtenteils in Form hydrophober Substanzen, während bei Stickstoff die Zunahme der hydrophilen Fraktion entscheidend war. Wie in den Böden der gemäßigten Breiten sanken die Konzentrationen mit zunehmender Bodentiefe. Hierbei wurde v. a. der hydrophobe DOM‐Anteil in der Bodenlösung stark reduziert. Die Veränderung der DOC‐Zusammensetzung im Kronenraum der Bäume und in der Auflage zeigt, dass hier primär Substanzen der hydrophoben Fraktion, die N‐arm sind, freigesetzt werden. Diese Substanzen werden im Mineralboden sorbiert und so der Bodenlösung entzogen. Im Gegensatz dazu ist DON mehr der labilen hydrophilen Fraktion zuzuordnen. Zumindest auf der Ackerfläche mit Kohlanbau scheint auch Mineralisation einen Beitrag zur Abnahme der DOC‐ und DON‐Konzentrationen zu leisten. Dies ist vermutlich Ergebnis einer Stimulation der mikrobiellen Aktivität durch Mineral‐N‐Düngung. Die ähnlichen Konzentrationen an DOC und DON sowie deren ähnliche Verteilung auf DOM‐Fraktionen in Unterböden und im Abfluss der Waldstandorte zeigen, dass hier Prozesse im Boden den DOM‐Austrag bestimmen. Der DON‐Anteil am Gesamt‐N in den Bachläufen der bewaldeten Einzugsgebiete liegt zwischen 50 und 73 %, was die Bedeutung von DOM für den Nährstoffaustrag aus Waldsystemen unterstreicht. Zusammenfassend zeigen DOC und DON Unterschiede in ihrer Dynamik sowohl unter Wald als auch unter Acker. Dies geht überwiegend auf die unterschiedliche Verteilung auf die stark sorbierende hydrophobe bzw. die leicht zersetzbare hydrophile Fraktion zurück.
    Keywords: Leaching ; C And N Export ; Land Use ; Organic Matter
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 9
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2002, Vol.165(4), pp.451-459
    Description: We tested the hypothesis whether organic matter in subsoils is a large contributor to organic carbon (OC) in terrestrial ecosystems and if survival of organic matter in subsoils is the result of an association with the soil mineral matrix. We approached this by analyzing two forest soil profiles, a Haplic Podzol and a Dystric Cambisol, for the depth distribution of OC, its distribution among density and particle‐size fractions, and the extractability of OC after destruction of the mineral phase by treatment with hydrofluoric acid (HF). The results were related to indicators of the soil mineralogy and the specific surface area. Finally, scanning electron microscopy combined with energy dispersive X‐ray spectroscopy (SEM‐EDX) was used to visualize the location of OC at mineral surfaces and associations with elements of mineral phases. The subsoils (B and C horizons) contained 40—50% of the soil OC including the organic forest floor layers. With increasing depth of soil profiles (1) the radiocarbon ages increased, and (2) increasing portions of OC were either HF‐soluble, or located in the density fraction 〉1.6 g cm, or in the clay fraction. The proportions of OC in the density fraction 〉1.6 g cm were closely correlated to the contents of oxalate and dithionite‐citrate‐bicarbonate‐extractable Fe ( = 0.93 and 0.88, 〈0.001). SEM‐EDX analyses suggested associations of OC with aluminum whereas silicon‐enriched regions were poor in OC. The specific surface area and the microporosity of the soil mineral matrix after destruction of organic matter were less closely correlated to OC than the extractable iron fractions. This is possibly due to variable surface loadings, depending on different OC inputs with depth. Our results imply that subsoils are important for the storage of OC in terrestrial ecosystems because of intimate association of organic matter with secondary hydrous aluminum and iron phases leading to stabilization against biological degradation. Stabilisierung organischer Substanz im Unterboden Wir gingen der Frage nach, inwieweit der Unterboden zur Speicherung organischen Kohlenstoffs in terrestrischen Ökosystemen beiträgt und welche Rolle dabei der Bindung an die Mineralphase zukommt. Untersucht wurden zwei Profile von Waldböden (Braunerde‐Podsol, schwach pseudovergleyte Braunerde). Wir bestimmten die Verteilung organischen Kohlenstoffs im Profil sowie in Dichte‐ und Korngrößenfraktionen. Außerdem wurde die Extrahierbarkeit von Kohlenstoff nach Zerstörung der Minerale mit Flusssäure (HF) ermittelt. Die Ergebnisse setzten wir mit chemischen Indikatoren der Mineralogie sowie der spezifischen Oberfläche in Beziehung. Rasterelektronenmikroskopische Aufnahmen in Kombination mit energiedispersiver Röntgenspektroskopie (REM‐EDX) wurden zur Visualisierung der organischen Substanzen auf Mineraloberflächen und ihrer Assoziation mit Elementen der Mineralphasen verwendet. Auf die Unterböden entfiel ein großer Teil (40—50%) des in den untersuchten Profilen einschließlich der organischen Auflagen gespeicherten organischen Kohlenstoffs. Mit zunehmender Bodentiefe nahmen (1) die C‐Alter zu und waren (2) zunehmende Anteile des Kohlenstoffs HF‐löslich bzw. in der Dichtefraktion 〉1.6 g cm und in den Tonfraktionen angereichert. Die C‐Anteile in der Dichtefraktion 〉1.6 g cm waren eng mit den Gehalten an oxalat‐ und dithionitlöslichem Eisen korreliert ( = 0.93 bzw. 0.88, 〈0.001). Die REM‐EDX‐Untersuchungen zeigten, dass die Akkumulation von Kohlenstoff häufig auch mit Aluminiumanreicherungen einhergehen. Zonen mit Siliciumanreicherungen waren dagegen immer an Kohlenstoff abgereichert. Die spezifische Oberfläche bzw. die Mikroporosität der Mineralmatrix nach Zerstörung der organischen Substanz waren weniger eng mit organischem Kohlenstoff korreliert als dies für extrahierbares Eisen der Fall war. Dies hängt möglicherweise mit der mit der Bodentiefe variierenden Kohlenstoffbelegung der Oberflächen infolge unterschiedlicher Einträge an organischer Substanz zusammen. Unsere Ergebnisse weisen Unterböden als wichtige Kohlenstoffspeicher terrestrischer Ökosysteme aus. Ursache ist die enge Bindung der organischen Substanz an sekundäre Aluminium‐ und Eisen‐Hydroxidphasen, die zu einer Stabilisierung gegenüber biologischem Abbau führt.
    Keywords: Soil Organic Matter ; Radiocarbon ; Density Separates ; Mineralogy ; Surface Area ; Microporosity ; Scanning Electron Microscopy ; Energy Dispersive X‐Ray Spectroscopy
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 10
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2019, Vol.182(4), pp.570-577
    Description: The Hedley fractionation has become the preeminent measure for estimating the bioavailability of phosphorus (P) in soils. However, mechanisms underlying P extractability have never been tested. We hypothesize that P sequentially extracted by individual steps can either be referred to a specific mineral source (Hypothesis 1) or to its binding strength to minerals (Hypothesis 2). We prepared mineral‐P associations in the laboratory using various secondary mineral phases and P forms (orthophosphate, phytic acid, ribonucleic acid), which were then subject to the Hedley sequential extraction scheme (anion exchange resin in form, 0.5 M NaHCO, 0.1 M NaOH, 1 M HCl, and concentrated HCl at 80°C). Extracts were analyzed for P as well as for the main mineral‐borne elements by inductively coupled plasma–optical emission spectroscopy (ICP–OES). In order to test if the observed mineral dissolution patterns match those of natural soils, we applied the Hedley fractionation to forest soils comprising various P stocks and measured in addition to extracted P also iron, aluminum, and calcium by ICPOES. Phosphorus extractability from mineral‐P associations differed between P forms and mineral phases. Adsorbed P always contributed to several or all extracts, Hypothesis 1 was thus not tenable. Aluminum hydroxide, allophane, ferrihydrite, and goethite completely dissolved during Hedley fractionation from the third extraction step onwards. Successive mineral dissolution also occurred for the soil samples. Thus, extracted P represents partly desorbed P from various soil constituents and partly P co‐released upon dissolution of various minerals. Consequently, also Hypothesis 2 could not be confirmed, ., the sequential extraction is not suitable to assess different binding strengths between P forms and minerals. We conclude that the method hardly provides information for studies aiming at the mechanistic understanding of P bioavailability in soil.
    Keywords: Hedley Fractionation ; Mineral‐Phosphorus Association ; Phosphorus Extractability ; Sequential Phosphorus Extraction
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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