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| Home > Publications database > Microbial carbon use efficiency of mineral-associated organic matter is related to its desorbability |
| Journal Article | FZJ-2025-01771 |
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2025
Elsevier Science
Amsterdam [u.a.]
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Please use a persistent id in citations: doi:10.1016/j.soilbio.2025.109740 doi:10.34734/FZJ-2025-01771
Abstract: Interactions between organic substances, minerals, and microorganisms are crucial for organic carbon (OC)stabilization in soil. We hypothesized that thresholds of sorption strength (described by the sorption coefficient ofthe Freundlich isotherms) and desorbability (i.e., the ratio of the amount desorbed to the amount sorbed) oforganic monomers control the extent of their microbial processing.Freundlich sorption isotherms and desorbability 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 intomicrobial biomass, and the 14C remaining in soil were quantified. Subsequently, the mineralization of incubatedsoils was observed for additional three weeks after glucose priming.The adsorption of carboxylic acids onto minerals exceeded that of (amino) sugars and phenylalanine, with theoverall highest amounts both adsorbed and retained after desorption with water for goethite. Assimilation ofmonomer 14C into microbial biomass and the microbial carbon use efficiency (CUE) of mineral-adsorbedmonomers 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 clayminerals. In terms of total amount of carbon retained in the soil, carboxylic acids adsorbed on goethite showedhighest values, emphasizing the significance of oxides for the stabilization of OC within soils. Priming of incu-bated soil with non-labeled glucose caused an additional mineralization of monomer-C, with the priming effectdecreasing from goethite to clay minerals.We conclude that sorption strength and desorbability shape microbial utilization of mineral-bound organiccompounds, but no universal thresholds determine bio-accessibility of sorbed organic compounds.
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