title: Structural Fe(II) Oxidation in Biotite by an Ectomycorrhizal Fungi Drives Mechanical Forcing.
abstract: Microorganisms are essential agents of Earth's soil weathering engine who help transform primary rock-forming minerals into soils. Mycorrhizal fungi, with their vast filamentous networks in symbiosis with the roots of most plants can alter a large number of minerals via local acidification, targeted excretion of ligands, submicron-scale biomechanical forcing, and mobilization of Mg, Fe, Al, and K at the hypha-biotite interface. Here, we present experimental evidence that Paxillus involutus-a basidiomycete fungus-in ectomycorrhizal symbiosis with Scots pine (Pinus sylvestris), is able to oxidize a substantial amount of structural Fe(II) in biotite. Iron redox chemistry, quantified by X-ray absorption near edge spectra on 13 fungi-biotite sections along three distinct hypha colonizing the [001] basal plane of biotite, revealed variable but extensive Fe(II) oxidation up to ∼2 μm in depth and a Fe(III)/Fetotal ratio of up to ∼0.8. The growth of Fe(III) hydroxide implies a volumetric change and a strain within the biotite lattice potentially large enough to induce microcrack formation, which are abundant below the hypha-biotite interface. This Fe(II) oxidation also leads to the formation of a large pool of Fe(III) (i.e., structural Fe(III) and Fe(III) oxyhydroxides) within biotite that could participate in the Fe redox cycling in soils.
authors.affiliation: Biogéochimie et Modélisation du Système Terre, Département Géosciences, Environnement et Société, Université Libre de Bruxelles , 50 av. F. D. Roosevelt, 1050 Brussels, Belgium.
authors.forename: Steeve
authors.initials: S
authors.lastname: Bonneville
authors.affiliation: Cohen Geochemistry, School of Earth and Environment, University of Leeds , Leeds LS2 9JT, United Kingdom.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Bray
authors.affiliation: Cohen Geochemistry, School of Earth and Environment, University of Leeds , Leeds LS2 9JT, United Kingdom.|GFZ, German Research Centre for Geosciences , Telegrafenberg, Potsdam 14473, Germany.
authors.forename: Liane G
authors.initials: LG
authors.lastname: Benning
mesh_terms: D005290:Ferric Compounds / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism*; D038821:Mycorrhizae / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D013559:Symbiosis
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds