Iron and aluminum association with microbially processed organic matter via meso-density aggregate formation across soils: organo-metallic glue hypothesis

Abstract. Global significance of iron (Fe) and aluminum (Al) for the storage of organic matter (OM) in soils and surface sediments is increasingly recognized. Yet specific metal phases involved or the mechanism behind metal–OM correlations frequently shown across soils remain unclear. We identified the allocation of major metal phases and OM to density fractions using 23 soil samples from five climate zones and five soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols) from Asia and North America, including several subsurface horizons and both natural and managed soils. Each soil was separated into four to seven density fractions using sodium polytungstate with mechanical shaking, followed by the sequential extraction of each fraction with pyrophosphate (PP), acid oxalate (OX), and finally dithionite–citrate (DC) to estimate pedogenic metal phases of different solubility and crystallinity. The concentrations of Fe and Al (per fraction) extracted by each of the three reagents were generally higher in meso-density fractions (1.8–2.4 g cm−3) than in the lower- or higher-density fractions, showing a unique unimodal pattern along the particle density gradient for each soil. Across the studied soils, the maximum metal concentrations were always at the meso-density range within which PP-extractable metals peaked at 0.3–0.4 g cm−3 lower-density range relative to OX- and DC-extractable metals. Meso-density fractions, consisting largely of aggregated clusters based on SEM observation, accounted for on average 56 %–70 % of total extractable metals and OM present in these soils. The OM in meso-density fractions showed a 2–23 unit lower C : N ratio than the lowest-density fraction of the respective soil and thus appeared microbially processed relative to the original plant material. The amounts of PP- and OX-extractable metals correlated positively with co-dissolved C across the soils and, to some extent, across the density fractions within each soil. These results led to a hypothesis which involves two distinct levels of organo-metal interaction: (1) the formation of OM-rich, mixed metal phases with fixed OM : metal stoichiometry followed by (2) the development of meso-density microaggregates via “gluing” action of these organo-metallic phases by entraining other organic and mineral particles such as phyllosilicate clays. Given that OM is mainly located in meso-density fractions, a soil's capacity to protect OM may be controlled by the balance of three processes: (i) microbial processing of plant-derived OM, (ii) dissolution of metals, and (iii) the synthesis of organo-metallic phases and their association with clays to form meso-density microaggregates. The current hypothesis may help to fill the gap between well-studied molecular-scale interaction (e.g., OM adsorption on mineral surface, coprecipitation) and larger-scale processes such as aggregation, C accrual, and pedogenesis.

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Iron and aluminum association with microbially processed organic matter via meso-density aggregate formation across soils: organo-metallic glue hypothesis

10.5194/soil-2020-32 ◽

2020 ◽

Author(s):

Rota Wagai ◽

Masako Kajiura ◽

Maki Asano

Keyword(s):

Organic Matter ◽

Particle Density ◽

Subsequent Development ◽

Density Range ◽

Aluminum Association ◽

Density Fractions ◽

Original Plant ◽

Extractable Metals ◽

Sodium Polytungstate ◽

Metal Phases

Abstract. Global significance of iron (Fe) and aluminum (Al) for the storage of organic matter (OM) in soils and surface sediments is increasingly recognized. Yet specific metal phases involved or the mechanism behind metal-OM correlations frequently shown across soils remain unclear. We identified density fraction locations of major metal phases and OM using 23 soil samples from 5 climate zones and 5 soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols), including several subsurface horizons and both natural and managed soils. Each soil was separated to 4 to 7 density fractions using sodium polytungstate with mechanical shaking, followed by the sequential extraction of each fraction with pyrophosphate (PP), acid oxalate (OX), and finally with dithionite-citrate (DC) to estimate pedogenic metal phases of different solubility and crystallinity. The extractable Fe and Al concentrations (per fraction) generally showed unique unimodal distribution along particle density gradient for each soil and each extractable metal phase. Across the studied soils, the maximum metal concentrations were always at meso-density range (1.8–2.4 g cm−3) within which PP-extractable metals peaked at 0.3–0.4 g cm−3 lower density range relative to OX- and DC-extractable metals. Meso-density fractions, consisted largely of microaggregates based on SEM observation, accounted for on average 56–70 % of total extractable metals and OM present in these soils. The OM in meso-density fractions appeared microbially processed from the original plant material. The amounts of PP- and OX-extractable metals correlated positively with co-dissolved C among the soils and, to some extent, across the density fractions within each soil. These results led to a hypothesis which involves two distinct levels of organo-metal interaction – the formation of OM-rich, mixed metal phases having relatively fixed OM : metal stoichiometry and subsequent development of meso-density microaggregates via gluing properties of these organo-metallic phases by incorporating other organic and mineral particles such as phyllosilicate clays. Given that stable OM is mainly located in meso-density fractions, soil's capacity to protect OM may be controlled by the balance of following three processes: (i) microbial processing of plant-derived OM, (ii) dissolution of metals, and (iii) the synthesis of organo-metallic phases and their association with clays to form meso-density microaggregates. The current hypothesis may help to fill the gap between well-studied molecular scales interaction (e.g., OM adsorption on mineral surface, coprecipitation) and larger-scale processes such as aggregation, C accrual, and pedogenesis.

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Co-localization of iron and aluminum with organic matter across a range of soils: a density-based approach

10.5194/egusphere-egu2020-22089 ◽

2020 ◽

Author(s):

Rota Wagai ◽

Masako Kajiura ◽

Maki Asano

Keyword(s):

Organic Matter ◽

Chemical Weathering ◽

Particle Density ◽

Soil Samples ◽

Metal Extraction ◽

Density Fractions ◽

Significant Control ◽

Wide Range ◽

Direct Binding ◽

Extractable Metals

Recent studies suggest significant control on pedogenic iron (Fe) and aluminum (Al) on organic matter (OM) storage and stability across a wide range of soils around the world. This information would be useful to improve or replace existing SOM models. On the other hand, metal extraction studies have shown that only minor portions of soil OM are directly bound to pedogenic Fe and Al. How can these metals control OM storage and stability without direct binding with bulk of OM? To answer this, an important step is to understand the location of the metals and OM within bulk soils. Sequential density fractionation is useful to examine their localizations because pure OM (e.g., plant detritus) and pure mineral particles (e.g., quartz, clay, Fe oxide) are the two endmembers along particle density gradient. We tested if Fe and Al released by chemical weathering are mainly present in association with OM using 22 soil samples from 11 sites spanning 5 climate zones, 5 soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols), and including several subsurface horizons and both natural and managed (upland and paddy) soils. Across all the studied soil samples, meso-density fractions (1.8-2.4 g cm-3) accounted for major portions of OM and the metals extractable by pyrophosphate, acid oxalate, and dithionite. We also found a strong stoichiometric relationship between the extractable metals and co-dissolved OM. We discuss the biogeochemical processes that may cause the co-localization of the metals and OM at the mesodensity across the soils from a wide range of pedogenic environments.

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Influence of elevated soil temperature and biochar application on organic matter associated with aggregate-size and density fractions in an arable soil

Agriculture Ecosystems & Environment ◽

10.1016/j.agee.2017.02.029 ◽

2017 ◽

Vol 241 ◽

pp. 79-87 ◽

Cited By ~ 14

Author(s):

Dennis Grunwald ◽

Michael Kaiser ◽

Simone Junker ◽

Sven Marhan ◽

Hans-Peter Piepho ◽

...

Keyword(s):

Organic Matter ◽

Soil Temperature ◽

Aggregate Size ◽

Arable Soil ◽

Density Fractions

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Predicting soil particle density from clay and soil organic matter contents

Geoderma ◽

10.1016/j.geoderma.2016.10.020 ◽

2017 ◽

Vol 286 ◽

pp. 83-87 ◽

Cited By ~ 33

Author(s):

P. Schjønning ◽

R.A. McBride ◽

T. Keller ◽

P.B. Obour

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Particle Density ◽

Soil Particle

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The dynamics of organic matter in soil size and density fractions traced by stable carbon isotopes

Chinese Journal of Geochemistry ◽

10.1007/bf02831528 ◽

2003 ◽

Vol 22 (2) ◽

pp. 179-184 ◽

Cited By ~ 2

Author(s):

Liu Qiming ◽

Wang Shijie ◽

Piao Hechun ◽

Ouyang Ziyuan

Keyword(s):

Organic Matter ◽

Carbon Isotopes ◽

Stable Carbon Isotopes ◽

Stable Carbon ◽

Density Fractions

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A Study of the Chemical and Physical Characteristics of the Soils from the South of Piauí for Soil-Cement Brick Production

Materials Science Forum ◽

10.4028/www.scientific.net/msf.869.112 ◽

2016 ◽

Vol 869 ◽

pp. 112-115 ◽

Cited By ~ 1

Author(s):

Francisca Pereira de Araújo ◽

Edson Cavalcanti Silva Filho ◽

João Sammy Nery de Souza ◽

Josy Anteveli Osajima ◽

Marcelo Barbosa Furtini

Keyword(s):

Organic Matter ◽

Particle Density ◽

Environmentally Friendly ◽

Physical Characteristics ◽

Chemical Characteristics ◽

The South ◽

Physical Chemical ◽

Soil Cement ◽

Made In

Soil-cement bricks are good examples of environmentally friendly products. This brick is the combination of soil with compacted cement with no combustion in its production. In this work the physical chemical characteristics of the soil from Piaui for producing this material were investigated. Samples of the soil were collected in three potteries from the county of Bom Jesus and pH analysis were carried out, as well as the rate of organic matter, texture, particle density, limits of liquidity and plasticity rates. The results have shown that the soils have acid tones (pH 5,49 a 6,11), which can be neutralized by adding cement, and organic matter percentages up to 1%. The samples have shown predominantly clay-rich textures with adequate plasticity limits, however, values of liquidity limits and particle density above recommended. Altogether, these soils tend to present viability concerning soil-cement brick production, provided that corrections with additives are made in order to minimize this effect.

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Particle densities of wetland soils in northern Alberta, Canada

Canadian Journal of Soil Science ◽

10.4141/s05-061 ◽

2006 ◽

Vol 86 (1) ◽

pp. 57-60 ◽

Cited By ~ 28

Author(s):

T. E. Redding ◽

K. J. Devito

Keyword(s):

Organic Matter ◽

Particle Density ◽

Physical Property ◽

Organic Soils ◽

Wetland Soil ◽

Loss On Ignition ◽

Simple Method ◽

Mean Values ◽

Northern Alberta ◽

Wetland Types

Particle density is a fundamental soil physical property, yet values of soil and organic matter particle density (ρs and ρo) vary widely in the literature. We measured particle density of organic soils from five wetland types, and from exposed sediments of drying ponds, in northern Alberta, Canada. Our measured values of organic soil and pond sediment ρs varied widely (1.43–2.39 Mg m-3); however, calculated values of ρo (1.34–1.52 Mg m-3) were relatively constant. The measured and calculated ρs and ρo values were similar to those obtained in published studies using similar methods, but were higher than the values provided in many reference texts. Given the relatively small variability in ρo, the use of mean values of ρo, combined with measurements of organic matter loss-on-ignition, shows promise as a simple method for obtaining reliable estimates of ρs across a range of wetland types. Key words: Particle density, peat, organic matter, wetland soil, loss-on-ignition

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Density fractions versus size separates: does physical fractionation isolate functional soil compartments?

Biogeosciences ◽

10.5194/bg-9-5181-2012 ◽

2012 ◽

Vol 9 (12) ◽

pp. 5181-5197 ◽

Cited By ~ 45

Author(s):

C. Moni ◽

D. Derrien ◽

P.-J. Hatton ◽

B. Zeller ◽

M. Kleber

Keyword(s):

Organic Matter ◽

Mineral Soil ◽

European Beech ◽

Nitrogen Dynamics ◽

Protective Mechanism ◽

Density Fractionation ◽

Adsorbed State ◽

Density Fractions ◽

Physical Fractionation ◽

Comprehensive Picture

Abstract. Physical fractionation is a widely used methodology to study soil organic matter (SOM) dynamics, but concerns have been raised that the available fractionation methods do not well describe functional SOM pools. In this study we explore whether physical fractionation techniques isolate soil compartments in a meaningful and functionally relevant way for the investigation of litter-derived nitrogen dynamics at the decadal timescale. We do so by performing aggregate density fractionation (ADF) and particle size-density fractionation (PSDF) on mineral soil samples from two European beech forests a decade after application of 15N labelled litter. Both density and size-based fractionation methods suggested that litter-derived nitrogen became increasingly associated with the mineral phase as decomposition progressed, within aggregates and onto mineral surfaces. However, scientists investigating specific aspects of litter-derived nitrogen dynamics are pointed towards ADF when adsorption and aggregation processes are of interest, whereas PSDF is the superior tool to research the fate of particulate organic matter (POM). Some methodological caveats were observed mainly for the PSDF procedure, the most important one being that fine fractions isolated after sonication can not be linked to any defined decomposition pathway or protective mechanism. This also implies that historical assumptions about the "adsorbed" state of carbon associated with fine fractions need to be re-evaluated. Finally, this work demonstrates that establishing a comprehensive picture of whole soil OM dynamics requires a combination of both methodologies and we offer a suggestion for an efficient combination of the density and size-based approaches.

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Thermal fractionation of soil organic matter produces fine-scale distributions of SOM age

10.5194/egusphere-egu21-15968 ◽

2021 ◽

Author(s):

Shane Stoner ◽

Carlos Sierra ◽

Marion Schrumpf ◽

Sebastian Dötterl ◽

Susan Trumbore

Keyword(s):

Thermal Stability ◽

Organic Matter ◽

Soil Organic Matter ◽

Chemical Oxidation ◽

Fine Scale ◽

Mineral Association ◽

Density Fractions ◽

Chemical Complexity ◽

Wide Range ◽

Carbon Release

Soil organic matter (SOM) is a complex collection of organic molecules of varying origin, structure, chemical activity, and mineral association. A wide array of laboratory methods exists to separate SOM based on qualitative, biological, chemical, and physical characteristics. However, all present conceptual and logistical limitations, including the requirement of a substantial amount soil material.An newly applied alternative method of fractionation relies on a conceptual analogue between biochemical stability in soil and thermal stability, e.g. more persistent SOM will require higher temperatures (greater energy inputs) to decompose than less persistent SOM. This accounts for both chemical complexity and mineral association as main factors in determining SOM persistence.In this method, carbon is released by heating SOM to 900&#176;C at a constant rate. The peaks of carbon release are grouped into activation energy pools, CO2 is collected, and analyzed for 13C and 14C. We seek to describe in finer detail the distribution of soil radiocarbon by adding another fractionation step following a different paradigm of SOM stability, and explore mineralogical effects on SOM quality and stability using thermal analysis, radiocarbon, and gas chromatography.Here, we analyzed bulk soil and soil fractions derived from density separation and chemical oxidation, as well as mineral horizons dominated by diverse mineralogies. Density fractions contained a wide range of radiocarbon activities and that young SOM is stabilized across multiple fractions, likely due to organomineral complexation. Initial results showed that soil minerals with limited stabilization potential released C at lower temperatures than those with diverse stabilization mechanisms. High-temperature sub-fractions contained the oldest carbon across fractions and minerals, thus supporting the assumption that thermal stability can be used as a limited analogue for stability in soil. We present a fine-scale distribution of radiocarbon in SOM and discuss the potential of this method for comparison with other fractionation techniques.

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Organo-Mineral Interactions Are More Important for Organic Matter Retention in Subsoil Than Topsoil

Soil Systems ◽

10.3390/soilsystems4010004 ◽

2020 ◽

Vol 4 (1) ◽

pp. 4 ◽

Cited By ~ 2

Author(s):

Vincent Poirier ◽

Isabelle Basile-Doelsch ◽

Jérôme Balesdent ◽

Daniel Borschneck ◽

Joann K. Whalen ◽

...

Keyword(s):

Organic Matter ◽

Crop Residue ◽

Crop Residues ◽

Clay Content ◽

X Ray Diffraction ◽

Density Fractions ◽

Organic Matter Concentration ◽

Fractionation Procedure ◽

Autochthonous Organic Matter ◽

C And N

Decomposing crop residues contribute to soil organic matter (SOM) accrual; however, the factors driving the fate of carbon (C) and nitrogen (N) in soil fractions are still largely unknown, especially the influence of soil mineralogy and autochthonous organic matter concentration. The objectives of this work were (1) to evaluate the retention of C and N from crop residue in the form of occluded and mineral-associated SOM in topsoil (0–20 cm) and subsoil (30–70 cm) previously incubated for 51 days with 13C-15N-labelled corn residues, and (2) to explore if specific minerals preferentially control the retention of residue-derived C and N in topsoil and subsoil. We used topsoil and subsoil having similar texture and mineralogy as proxies for soils being rich (i.e., topsoil) and poor (i.e., subsoil) in autochthonous organic matter. We performed a sequential density fractionation procedure and measured residue-derived C and N in occluded and mineral-associated SOM fractions, and used X-ray diffraction analysis of soil density fractions to investigate their mineralogy. In accordance with our hypothesis, the retention of C and N from crop residue through organo-mineral interactions was greater in subsoil than topsoil. The same minerals were involved in the retention of residue-derived organic matter in topsoil and subsoil, but the residue-derived organic matter was associated with a denser fraction in the subsoil (i.e., 2.5–2.6 g cm−3) than in the topsoil (i.e., 2.3–2.5 g cm−3). In soils and soil horizons with high clay content and reactive minerals, we find that a low SOM concentration leads to the rapid stabilization of C and N from newly added crop residues.

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