Distribution of trinitrotoluene between aqueous and solid phase soil organic matter

Redox-driven changes in Fe crystallinity and speciation may affect soil organic matter (SOM) stabilization and carbon (C) turnover, with consequent influence on global terrestrial soil organic carbon (SOC) cycling.&#160;Under reducing conditions, increasing concentrations of Fe(II) released in solution from the reductive dissolution of Fe (hydr)oxides may accelerate ferrihydrite transformation, although our understanding of the influence of SOM on these transformations is still lacking.&#160;Here, we evaluated abiotic Fe(II)-catalyzed mineralogical changes in Fe (hydr)oxides in bulk soils and size-fractionated SOM pools (for comparison, fine silt plus clay, FSi+Cl, and fine sand, FSa) of an agricultural soil, unamended or amended with biochar, municipal solid waste compost, and a combination of both.&#160;FSa fractions showed the most significant Fe(II)-catalyzed ferrihydrite transformations with the consequent production of well-ordered Fe oxides irrespective of soil amendment, with the only exception being the compost-amended soils. In contrast, poorly crystalline ferrihydrite still constituted ca. 45% of the FSi+Cl fractions of amended soils, confirming the that the higher SOM content in this fraction inhibits atom exchange between aqueous Fe(II) and the solid phase. Building on our knowledge of Fe(II)-catalyzed mineralogical changes in simple systems, our results evidenced that the mechanisms of abiotic Fe mineral transformations in bulk soils depend on Fe mineralogy, organic C content and quality, and organo-mineral associations that exist across particle-size SOM pools. Our results underline that in the fine fractions the increase in SOM due to organic amendments can contribute to limiting abiotic Fe(II)-catalyzed ferrihydrite transformation, while coarser particle-size fractions represent an understudied pool of SOM subjected to Fe mineral transformations.&#160;

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Plant organic matter inputs exert a strong control on soil organic matter decomposition in a thawing permafrost peatland

10.1101/2021.10.20.465126 ◽

2021 ◽

Author(s):

Rachel M Wilson ◽

Moira Hough ◽

Brittany Verbeke ◽

Suzanne Hodgkins ◽

Jeff Chanton ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Plant Extracts ◽

Molecular Level ◽

Solid Phase ◽

Gas Emissions ◽

Microbial Decomposition ◽

Vegetation Shifts ◽

Ft Ir ◽

Strong Control

Peatlands are a climate critical carbon (C) reservoir that will likely become a C source under continued warming. A strong relationship between plant tissue chemistry and the soil organic matter (SOM) that fuels C gas emissions is inferred, but rarely examined at the molecular level. Here we compared Fourier transform infrared (FT-IR) spectroscopy measurements of solid phase functionalities in plants and SOM to ultra-high-resolution mass spectrometric analyses of plant and SOM water extracts across a palsa-bog-fen thaw and moisture gradient in an Arctic peatland. From these analyses we calculated the C oxidation state (NOSC), a measure which can be used to assess organic matter quality. Palsa plant extracts had the highest NOSC, indicating high quality, while extracts of Sphagnum, which dominated the bog, had the lowest NOSC. The percentage of plant compounds that are less bioavailable and accumulate in the peat, increases from palsa (25%) to fen (41%) to bog (47 %), reflecting the pattern of percent Sphagnum cover. The pattern of NOSC in the plant extracts was consistent with the high number of consumed compounds in the palsa and low number of consumed compounds in the bog. However, in the FT-IR analysis of the solid phase bog peat, carbohydrate content was high implying higher quality SOM. We explain this discrepancy as the result of low solubilization of bog SOM facilitated by the low pH in the bog which makes the solid phase carbohydrates less available to microbial decomposition. Plant-associated lignins and tannins declined in the unsaturated palsa peat indicating decomposition, but accumulated in the bog and fen peat where decomposition was presumably inhibited by the anaerobic conditions. A molecular-level comparison of the aboveground C sources and peat SOM demonstrates that climate-associated vegetation shifts in peatlands are important controls on the mechanisms underlying changing C gas emissions.

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Adsorption of Fulvic Acid and Water Extractable Soil Organic Matter on Kaolinite and Muscovite

Agronomy ◽

10.3390/agronomy11122420 ◽

2021 ◽

Vol 11 (12) ◽

pp. 2420

Author(s):

Ksenia Kolchanova ◽

Inna Tolpeshta ◽

Yulia Izosimova

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Fulvic Acid ◽

Electrostatic Interactions ◽

Hydrophobic Interactions ◽

Solid Phase ◽

Size Composition ◽

Size Exclusion ◽

Extractable Organic Matter ◽

Water Extractable

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N2 molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH < 5, more WEOM is adsorbed on muscovite than on kaolinite.

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Diffusion and sorption of water vapor and benzene within a dry model soil organic matter

Water Science & Technology ◽

10.2166/wst.1997.0269 ◽

1997 ◽

Vol 35 (7) ◽

pp. 131-138

Author(s):

Tsair-Fuh Lin

Keyword(s):

Experimental Data ◽

Organic Matter ◽

Water Vapor ◽

Soil Organic Matter ◽

Gas Phase ◽

Sorption Isotherm ◽

Solid Phase ◽

Pore Diffusion ◽

Desorption Kinetics ◽

Model Soil

The sorption behavior of water vapor and benzene within a dry model soil organic matter (SOM), peat, was studied. An electrobalance system was employed to determine both the equilibrium sorption isotherm and sorption-desorption kinetics. The sorption isotherm for water vapor was found to resemble that previously reported for this sample, while the sorption isotherm for benzene could not be determined, due to a failure to obtain reproducible sorption capacity. In the kinetic study, strong asymmetries between sorption and desorption rates were observed for both water vapor and benzene. Two diffusion models, accounting for either gas-phase pore diffusion within peat grains or solid-phase diffusion within microspheres of SOM, were used to interpret the asymmetric sorption rate data. Considering gas-phase pore diffusion only, the model resolved the asymmetry of sorption rates and described the experimental data very well for water vapor at three different concentrations. However, the pore diffusion model failed to capture the dominant feature of the experimental data for benzene. As a refinement, a model assuming that solid-phase intra-SOM diffusion is the rate-limiting mechanism produced a better description of the experimental data.

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Characterizing soil organic matter differences among extracts and the solid phase – the role of conservation tillage

10.5194/egusphere-egu2020-6997 ◽

2020 ◽

Author(s):

Gergely Jakab ◽

Tibor Filep ◽

Csilla Király ◽

Balázs Madarász ◽

Dóra Zacháry ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Solid Phase ◽

Conservation Tillage ◽

Fine Fraction ◽

Water Soluble ◽

Carbon Pools ◽

Organic Carbon Content

Soil organic matter (SOM) is in the focus of research as it plays crucial role in soil fertility, carbon sequestration, and all adsorption related processes in the soil. Nevertheless, its compound and the methods to investigate it are rather diverse. Some approach prefers to define different theoretical carbon pools in the soil based on input and mineralization dynamics using mean residence times. Other studies apply physical and/or chemical fractionations of the soil to separate the various eg. mineral phase associated or aggregate occluded carbon pools to gain less heterogeneous material. However, in practice, these two approaches are hardly met each other. As a considerable part of SOM is strongly associated with the mineral colloid fraction or even cations its investigation reveals the question of extractions. Traditional methods aimed to extract pure SOM fractions such as fulvic and humic acids (FA; HA)&#160; and characterized the whole SOM based on them, even though these pure fractions represented only a small part of the total SOM and were not present under natural conditions. Recent methods try to characterize the SOM using in situ samples where the role of organic mineral complexes is still not fully understood. As a result, findings based on several approaches are hardly comparable with each other. The present study aims to characterize SOM based on parallel in situ solid-phase investigation FA separation, and water dissolved organic matter extraction. The study site is a haplic Luvisol under plowing and conservation tillage. Fourier transform infrared spectroscopy on the solid phase fractions resulted in an inverse proportion between organic carbon content and aromaticity independently from tillage. The aggregate occluded SOM was characterized by the lack of aliphatic components, whereas the fine fraction, and the bulk soil associated SOM seemed to be rich in them. The water-soluble SOM revealed molecular size increase in both the fine fraction related and the aggregate occluded organic matter owing to plowing, nonetheless, aggregates occluded the same sized OM molecules as those attached to the fine fraction. In general, FA fractions provided more humified organic matter, whereas water dissolved SOM showed a more intensive microbiome origin. The photometric properties of the FA fractions did not differ between the tillage systems, except for the SUVA254, which provided higher aromaticity under conservation tillage due to the lack of plowing. Also, the water-soluble part of SOM showed more humified composition and increased aromaticity under conservation tillage compared to plowing tillage. As a consequence, beneath the fingerprint of recent microbial activity, DOM reflects soil organic matter composition as well, therefore it seems to be suitable as a direct SOM proxy. The present research was supported by the Hungarian National Research and Innovation Office (NKFIH) K-123953, which is kindly acknowledged.

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