Distinctive organic matter pools among particle-size fractions detected by solid-state13C-NMR, δ13C and δ15N analyses only after strong dispersion in an allophanic Andisol

Asano, Masaharu; Wagai, Rota

doi:10.1080/00380768.2014.982492

Cited by 13 publications

(8 citation statements)

References 36 publications

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“…Aromatic C has been reported to be a major form stabilized C in some Andisols via preservation of pyrogenic C [68] and/or sorption of high C:N plant derived organic matter onto RI phase [69]. In our study, however, the solid-state 13 C-NMR showed lower aromatic C in the 0.2-2 µm fraction compared to the 2-53 µm fraction and bulk soil sample [43]. C-NEXAFS could distinguish the source of aromatic C between char and non-pyrogenic compounds.…”

Section: 2carbon Forms Of the Organo-mineral/metal Nanocompositcontrasting

confidence: 75%

“…The whole observed region and four C-rich regions selected showed the dominance of amide and carboxylic C, suggesting that potentially-labile C was the main C form in the observed regions and thus presumably in OMN. These compounds appeared to be microbially-derived because the 0.2-2 µm fraction had lower C:N ratio and greater enrichment of 13 C and 15 N than 2-53 µm fraction and bulk soil [43].…”

Section: 2carbon Forms Of the Organo-mineral/metal Nanocompositmentioning

confidence: 99%

“…The treatment ranged from mechanical shaking to maximum dispersion (sodium saturation followed by sonication at 5 kJ mL −1 ), above which no more clay-sized particles were released by physical means. The following five unique features of aggregate hierarchy were identified [42,43]. First, hierarchical structure was present at much smaller spatial scale (<53 µm) than previously shown for other soil types [44].…”

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confidence: 90%

“…In this study, we thus attempted to identify OMN which was presumed to be more abundant in sonication-resistant, finer-sized fractions. We hypothesized that the spatial distribution of organic C matches with that of RI phase within a particle from the 0.2-2 µm size fraction of the Andisol we previously examined [42,43]. A potential pitfall is the possible re-aggregation of subunits, which can occur at unknown degrees during the fractionation and preparation steps for microscopic observation.…”

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confidence: 99%

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In Search of a Binding Agent: Nano-Scale Evidence of Preferential Carbon Associations with Poorly-Crystalline Mineral Phases in Physically-Stable, Clay-Sized Aggregates

et al. 2018

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Mechanisms of protecting soil carbon (C) are still poorly understood despite growing needs to predict and manage the changes in soil C or organic matter (OM) under anticipated climate change. A fundamental question is how the submicron-scale interaction between OM and soil minerals, especially poorly-crystalline phases, affects soil physical aggregation and C stabilization. Nano-sized composites rich in OM and poorly-crystalline mineral phases were presumed to account for high aggregate stability in the Andisol we previously studied. Here we searched for these nanocomposites within a sonication-resistant aggregate using scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure (NEXAFS) as well as electron microscopy (SEM, TEM). Specifically, we hypothesized that nanometer-scale spatial distribution of OM is controlled by poorly-crystalline minerals as both co-exist as physically-stable nanocomposites. After maximum dispersion of the cultivated Andisol A-horizon sample in water, one aggregate (a few µm in diameter) was isolated from 0.2-2 µm size fraction which accounted for 44-47% of total C and N and 50% of poorly-crystalline minerals in bulk soil. This fraction as well as <0.2 µm fraction had much higher extractable Al and Fe contents and showed greater increase in specific surface area (N 2 -BET) upon OM oxidation compared to bulk and >2 µm size fractions, implying high abundance of the nanocomposites in the smaller fractions. The isolated aggregate showed a mosaic of two distinctive regions. Smooth surface regions showed low adsorption intensity of carbon K-edge photon energy (284-290 eV) with well-crystalline mineralogy, whereas rough surface regions had features indicative of the nanocomposites: aggregated nanostructure, high C intensity, X-ray amorphous mineral phase, and the dominance of Si, O, Al, and Fe based on SEM/EDX and TEM/EDX. Carbon functional group chemistry assessed by NEXAFS showed the dominance of amide and carboxyl C over aromatic and aliphatic C with some variation among the four rough surface regions. Together with C and N isotopic patterns among the size fractions (relatively low C:N ratio, high 15 N natural abundance, and more Soil Syst. 2018, 2, 32 2 of 18 positive ∆ 14 C of the <2 µm fractions), our results provided the direct evidence of preferential binding of microbially-altered, potentially-labile C with poorly-crystalline mineral phases at submicron scale. The role of the nanocomposite inferred from this study may help to bridge the knowledge gap between physical aggregation process and biogeochemical reactions taking place within the soil physical structure.

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Section: 2carbon Forms Of the Organo-mineral/metal Nanocompositcontrasting

confidence: 75%

Section: 2carbon Forms Of the Organo-mineral/metal Nanocompositmentioning

confidence: 99%

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confidence: 90%

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In Search of a Binding Agent: Nano-Scale Evidence of Preferential Carbon Associations with Poorly-Crystalline Mineral Phases in Physically-Stable, Clay-Sized Aggregates

et al. 2018

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“…Rather, they focused on the OM‐mineral interactions, the formation of the organo‐mineral‐associations as composite building units of the microaggregates, the stabilization of OM, or protection against microbial attack. Asano and Wagai () revealed that the sonication‐resistant, nano‐sized organo‐mineral composites acted as a ‘persistent binding agent' for microaggregate formation, at least in andic soils. They further showed that these composites were enriched in microbially‐processed OM.…”

Section: Mechanisms Of Microaggregate Formationmentioning

confidence: 99%

Microaggregates in soils

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Amelung

Gerzabek

et al. 2017

J. Plant Nutr. Soil Sci.

670

439

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All soils harbor microaggregates, i.e., compound soil structures smaller than 250 μm. These microaggregates are composed of diverse mineral, organic and biotic materials that are bound together during pedogenesis by various physical, chemical and biological processes. Consequently, microaggregates can withstand strong mechanical and physicochemical stresses and survive slaking in water, allowing them to persist in soils for several decades. Together with the physiochemical heterogeneity of their surfaces, the three-dimensional structure of microaggregates provides a large variety of ecological niches that contribute to the vast biological diversity found in soils. As reported for larger aggregate units, microaggregates are composed of smaller building units that become more complex with increasing size. In this context, organo-mineral associations can be considered structural units of soil aggregates and as nanoparticulate fractions of the microaggregates themselves. The mineral phases considered to be the most important as microaggregate forming materials are the clay minerals and Fe-and Al-(hydr)oxides. Within microaggregates, minerals are bound together primarily by physicochemical and chemical interactions involving cementing and gluing agents. The former comprise, among others, carbonates and the short-range ordered phases of Fe, Mn, and Al. The latter comprise organic materials of diverse origin and probably involve macromolecules and macromolecular mixtures. Work on microaggregate structure and development has largely focused on organic matter stability and turnover. However, little is known concerning the role microaggregates play in the fate of elements like Si, Fe, Al, P, and S. More recently, the role of microaggregates in the formation of microhabitats and the biogeography and diversity of microbial communities has been investigated. Little is known regarding how microaggregates and their properties change in time, which strongly limits our understanding of micro-scale soil structure dynamics. Similarly, only limited information is available on the mechanical stability of microaggregates, while essentially nothing is known about the flow and transport of fluids and solutes within the micro-and nanoporous microaggregate systems. Any quantitative approaches being developed for the modeling of formation, structure and properties of microaggregates are, therefore, in their infancy. We respond to the growing awareness of the importance of microaggregates for the structure, properties and functions of soils by reviewing what is currently known about the formation, composition and turnover of microaggregates. We aim to provide a better understanding of their role in soil function, and to present the major unknowns in current microaggregate research. We propose a harmonized concept for aggregates in soils that explicitly considers the structure and build-up of microaggregates and the role of organo-mineral associations. We call for experiments, studies and modeling endeavors that will link informatio...

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Chemical nature of soil organic carbon under different long-term fertilization regimes is coupled with changes in the bacterial community composition in a Calcaric Fluvisol

Lin

et al. 2018

Biol Fertil Soils

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Distinctive organic matter pools among particle-size fractions detected by solid-state¹³C-NMR, δ¹³C and δ¹⁵N analyses only after strong dispersion in an allophanic Andisol

Cited by 13 publications

References 36 publications

In Search of a Binding Agent: Nano-Scale Evidence of Preferential Carbon Associations with Poorly-Crystalline Mineral Phases in Physically-Stable, Clay-Sized Aggregates

In Search of a Binding Agent: Nano-Scale Evidence of Preferential Carbon Associations with Poorly-Crystalline Mineral Phases in Physically-Stable, Clay-Sized Aggregates

Microaggregates in soils

Chemical nature of soil organic carbon under different long-term fertilization regimes is coupled with changes in the bacterial community composition in a Calcaric Fluvisol

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