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  1. Variation in the Molecular Structure and Radiocarbon Abundance of Mineral-Associated Organic Matter across a Lithosequence of Forest Soils

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    Author(s): Katherine Heckman; Heather Throckmorton; William Horwath; Christopher Swanston; Craig Rasmussen
    Date: 2018
    Source: Soil Systems
    Publication Series: Scientific Journal (JRNL)
    Station: Northern Research Station
    DOI: https://doi.org/10.3390/soilsystems2020036
    PDF: View PDF  (570.0 KB)

    Description

    Soil mineral assemblage influences the abundance and mean residence time of soil organic matter both directly, through sorption reactions, and indirectly, through influences on microbial communities. Though organo-mineral interactions are at the heart of soil organic matter cycling, current models mostly lack parameters describing specific mineral assemblages or phases, and treat the mineral-bound pool as a single homogenous entity with a uniform response to changes in climatic conditions. We used pyrolysis GC/MS in combination with stable isotopes and radiocarbon abundance to examine mineral-bound soil organic matter fractions from a lithosequence of forest soils. Results suggest that different mineral assemblages tend to be associated with soil organics of specific molecular composition, and that these unique suites of organo-mineral complexes differ in mean residence time. We propose that mineralogy influences the composition of the mineral-bound soil organic matter pool through the direct influence of mineral surface chemistry on organo-mineral bond type and strength in combination with the indirect influence of soil acidity on microbial community composition. The composition of the mineral-bound pool of soil organic matter is therefore partially dictated by a combination of compound availability and sorption affinity, with compound availability controlled in part by microbial community composition. Furthermore, results are suggestive of a preferential sorption of N-containing moieties in Fe-rich soils. These bonds appear to be highly stable and confer extended mean residence times.

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    Citation

    Heckman, Katherine; Throckmorton, Heather; Horwath, William; Swanston, Christopher; Rasmussen, Craig. 2018. Variation in the Molecular Structure and Radiocarbon Abundance of Mineral-Associated Organic Matter across a Lithosequence of Forest Soils. Soil Systems. 2(2): 36-. 12 p. https://doi.org/10.3390/soilsystems2020036.

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    Keywords

    soil organic matter, organo-mineral, lithosequence, radiocarbon, pyrolysis GC/MS

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