Arbuscular mycorrhizal fungi as biological entry points to mineral-associated organic matter formation

Arbuscular mycorrhizal fungi (AMF) are central components of terrestrial ecosystems, linking plant carbon inputs to soil microbial communities and mineral surfaces. While mineral-associated organic matter (MAOM) is often conceptualized as the product of dissolved organic matter sorption, growing evidence suggests that living mycorrhizal biomass may represent a primary entry point for carbon stabilization, with necromass formation and mineral association emerging downstream of biological colonization.

Here, we present an exploratory field-based study examining how AMF and their associated microbial communities colonize mineral substrates with contrasting surface chemistry under realistic soil conditions. Mineral-filled pouches containing quartz, kaolinite, montmorillonite, or goethite were deployed in agricultural soils under long-term contrasting tillage regimes (tilled vs. no-till), known to host distinct AMF communities. To decouple dissolved organic matter inputs from active mycorrhizal colonization, mineral substrates were deployed under two access conditions: 1 µm mesh bags permitting dissolved organic matter diffusion only, and 30 µm mesh bags allowing access by AMF hyphae and associated microorganisms.

AMF colonization was quantified via hyphal length measurements, and microbial and general fungal biomass were assessed using targeted qPCR. Broader microbial community composition associated with minerals was characterized through DNA extraction and sequencing. In parallel, non-targeted metabolomics will be used to explore the biochemical signatures associated with colonizing communities, and Fourier Transform Infrared (FTIR) spectroscopy will provide insights into emerging mineral–organic associations.

This study explicitly positions AMF-driven colonization as a first-order process structuring mineral–organic interactions, rather than a secondary modifier of mineral sorption. By identifying which minerals are preferentially colonized by AMF, and how colonization patterns vary with mineralogy and tillage regime, this work contributes to a biologically grounded understanding of soil carbon stabilization. Resolving AMF/mineral associations represents a critical step toward integrating mycorrhizal ecology into mechanistic models of soil biogeochemistry and ecosystem functioning.