Stabilization of Soil Organic Carbon as Influenced by Clay Mineralogy

Despite decades of research progress, ecologists are still debating which pools and fluxes provide nitrogen (N) to plants and soil microbes across different ecosystems. Depolymerization of soil organic N is recognized as the rate-limiting step in the production of bioavailable N, and it is generally assumed that detrital N is the main source. However, in many mineral soils, detrital polymers constitute a minor fraction of total soil organic N. The majority of organic N is associated with clay-sized particles where physicochemical interactions may limit the accessibility of N-containing compounds. Although mineralassociated organic matter (MAOM) has historically been considered a critical, but relatively passive, reservoir of soil N, a growing body of research now points to the dynamic nature of mineral-organic associations and their potential for destabilization. Here we synthesize evidence from biogeoscience and soil ecology to demonstrate how MAOM is an important, yet overlooked, mediator of bioavailable N, especially in the rhizosphere. We highlight several biochemical strategies that enable plants and microbes /doi.org/10.1007/s10533-018-0459-5 to disrupt mineral-organic interactions and access MAOM. In particular, root-deposited low-molecularweight exudates may enhance the mobilization and solubilization of MAOM, increasing its bioavailability. However, the competitive balance between the possible fates of N monomers-bound to mineral surfaces versus dissolved and available for assimilation-will depend on the specific interaction between mineral properties, soil solution, mineral-bound organic matter, and microbes. Building off our emerging understanding of MAOM as a source of bioavailable N, we propose a revision of the Schimel and Bennett (Ecology 85:591-602, 2004) model (which emphasizes N depolymerization), by incorporating MAOM as a potential proximal mediator of bioavailable N.123 Biogeochemistry (2018) 139:103-122 https:/

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“…Mineral identity plays a major role in the nature of organo-mineral bonds (Singh et al 2017) (Fig. 3) and potentially in MAOM bioavailability.…”

Section: Strength Of Organo-mineral Associationsmentioning

confidence: 99%

Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes

et al. 2018

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“…In addition to fertilization, clay and soil moisture content are main factors in controlling DOC concentrations in the soil pore water (De Troyer et al, 2014). Clay is providing a large surface area for DOC sorption (Huang et al, 2019;Nguyen and Marschner, 2014;Singh et al, 2018), and, sorption of DOC onto clay is mostly irreversible (Avneri-Katz et al, 2017). Due to the occupation of binding sites, DOC sorption decrease with increasing organic carbon content (Bolan et al, 2011).…”

Section: Amounts Of Leached Docmentioning

confidence: 99%

Short-term effects of fertilization on dissolved organic matter (DOM) in soil leachate

Tiefenbacher

Weigelhofer

Klik

et al. 2020

Preprint

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Abstract. Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the composition and concentration of dissolved organic matter leached from soils into adjacent aquatic ecosystems. In order to investigate the immediate response of DOM leaching to fertilization, we conducted a short-term (45 day) lysimeter experiment with undisturbed silt loam and loamy sand soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha−1. After fertilization, soil leachate was collected in 6-days intervals. Dissolved organic carbon concentrations (DOC) were measured with gas chromatography, while shifts in DOM composition were analysed using absorbance and excitation- emission fluorescence indices from peak-picking as well as from PARAFAC analysis. During the first 12 days, fertilization of a silt loam reduced DOC concentrations in the leachate and shifted its composition towards more microbial- like compounds. Additionally, the discrepancy in DOM composition between fertilizer and control treatments of a silt loam increased with time. However, in loamy sand only mineral fertilization affected organic matter leaching and decreased DOC concentrations in the leachate during the first 12 days. Furthermore, mineral fertilization of the loamy sand led to DOM compounds with low molecular size in the first 12 days. Our results show that fertilization tends to increase microbial transformed DOM, while it reduces leached DOC concentrations. Furthermore, the magnitude of fertilization on DOC concentrations and DOM composition was highly depending on the soil texture they originate from. However, in our set-up, the experimental soil units were restricted to a soil depth of 16 cm (Ap horizon). At ecosystem level, a sufficiently long soil passage might mitigate the impact of fertilization on soil DOM.

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“…According to Churchman [3], clay minerals in the soil context are "secondary inorganic compounds of <2 μm size" including Fe, Al, and Mn oxides (hydroxides and oxyhydroxides), as well as noncrystalline phases. Importantly, they are the most reactive and important inorganic components in soils, and they occur commonly in close association with the most reactive organic matter [4,5]. Clays influence soil function through both their bulk properties and their associations with their huge outer/inner surfaces (e.g., cation exchange capacity [6]).…”

Section: Introductionmentioning

confidence: 99%

Visible and Near-Infrared Reflectance Spectroscopy for Investigating Soil Mineralogy: A Review

Fang

Hong

Zhao

et al. 2018

Journal of Spectroscopy

106

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Clay minerals are the most reactive and important inorganic components in soils, but soil mineralogy classifies as a minor topic in soil sciences. Revisiting soil mineralogy has been gradually required. Clay minerals in soils are more complex and less well crystallized than those in sedimentary rocks, and thus, they display more complicated X-ray diffraction (XRD) patterns. Traditional characterization methods such as XRD are usually expensive and time-consuming, and they are therefore inappropriate for large datasets, whereas visible and near-infrared reflectance spectroscopy (VNIR) is a quick, cost-efficient, and nondestructive technique for analyzing soil mineralogic properties of large datasets. The main objectives of this review are to bring readers up to date with information and understanding of VNIR as it relates to soil mineralogy and attracts more attention from a wide variety of readers to revisit soil mineralogy. We begin our review with a description of fundamentals of VNIR. We then review common methods to process soil VNIR spectra and summary spectral features of soil minerals with particular attention to those <2 μm fractions. We further critically review applications of chemometric methods and related model building in spectroscopic soil mineral studies. We then compare spectral measurement with multivariate calibration methods, and we suggest that they both produce excellent results depending on the situation. Finally, we suggest a few avenues of future research, including the development of theoretical calibrations of VNIR more suitable for various soil samples worldwide, better elucidation of clay mineral-soil organic carbon (SOC) interactions, and building the concept of integrated soil mapping through combined information (e.g., mineral composition, soil organic matter-SOM, SOC, pH, and moisture).

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Stabilization of Soil Organic Carbon as Influenced by Clay Mineralogy

Cited by 181 publications

References 208 publications

Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes

Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes

Short-term effects of fertilization on dissolved organic matter (DOM) in soil leachate

Visible and Near-Infrared Reflectance Spectroscopy for Investigating Soil Mineralogy: A Review

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