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| Home > Publications database > Soil minerals as boundary condition of microbial carbon use of sorbed organic model compounds |
| Conference Presentation (Plenary/Keynote) | FZJ-2025-03203 |
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2025
Abstract: Sorption strength of organic molecules to minerals is among the boundary conditions that shape the channel for energy and matter use by the microbial community of soil systems. Although the stabilization of organic matter against microbial use and mineralization in soil has been linked to sorption, exact mechanism on stabilization of organic compound on mineral surfaces remain to be elucidated. Based on the interactions of organic substances, minerals and microorganisms we hypothesized that thresholds of sorption strength of organic monomers to soil minerals control the extent of their microbial processing.Freundlich sorption isotherms and desorbability (i.e., the ratio of the amount desorbed to the amount sorbed) of uniformly 14C-labeled glucose, acetylglucosamine, phenylalanine, salicylic acid, and citric acid onto goethite, kaolinite, and illite were studied in batch experiments. Monomers adsorbed to minerals were mixed with loamy and sandy arable topsoil and incubated at 25°C. Mineralization of mineral-adsorbed monomers was observed over three weeks, after which the assimilation into microbial biomass, and the 14C remaining in soil were quantified. Additional experiments with isothermal titration calorimetry (ITC) were used with unlabeled model organic substances to each mineral to characterize the organic compound-mineral binding thermodynamically.The adsorption of carboxylic acids onto minerals yielded only for goethite sorption quantifiable signals with ITC for thermodynamic characterization. We also observed that the adsorption nof carboxylic acids onto minerals exceeded that of (amino) sugars and phenylalanine with the overall highest amounts for goethite. Thresholds of sorption strength were described for all minerals by the sorption coefficient of the Freundlich isotherms and the desorbability of organic monomers. Assimilation of monomer 14C into microbial biomass and the microbial carbon use efficiency (CUE) of mineral-adsorbed monomers in both soils increased linearly with the monomer desorbability from mineral phases. Furthermore, the CUEs of monomers adsorbed to goethite were lower than those of the same monomers adsorbed to clay minerals [1]. We conclude that sorption strength and desorbability shape microbial utilization of mineral-bound organic compounds, but no universal thresholds determine bio-accessibility of sorbed organic compounds. In terms of total amount of carbon retained in the soil, carboxylic acids adsorbed on goethite showed highest values, emphasizing the significance of oxides for the stabilization of OC within soils.
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