Abstract
Fungi dissolve soil minerals by acidification and mechanical disruption. Dissolution may occur at the microscale (contact between fungus and mineral) and medium scale (entire mineral grains). Mineral weathering by fungi and other microorganisms is thought to be of significant global contribution, perhaps producing specific weathering signatures. We report fungal dissolution of phlogopite mica in experiments with three fungal strains (Alternaria tenuissima, Cladosporium cladosporioides, Stilbella sp.) on solid medium for 30 days at 21 °C and 96–100% relative humidity. The study used variable-pressure SEM-EDS equipped with charge contrast imaging. Statistical analysis of the results discriminated between the weathering activities of the three fungal species, which increased from Stilbella sp. to C. cladosporioides to A. tenuissima, in agreement with the respective decreasing pH in the media (6.4, 5.8, 5.2 ± 0.03). Phlogopite weathering features were irregular and variable, apparently not caused by direct contact with fungal hyphae. EDS values indicated two or more dissolution mechanisms, one of them suggesting cation rearrangement in the mica towards formation of Al-rich smectite. Intimate fungus-mineral interaction was observed, and the lack of observable dissolution traces from such contact interaction is interpreted as the result of effacing by the more intense acid leaching operating at larger scale.
Highlights
8 MPa, and can produce structural alterations of phyllosilicates (Bonneville et al, 2009), possibly by causing strain in the mineral during hyphal growth
Cladosporium produced an abundant mass of conidia but little mycelium, 300 which grew dispersed on the surface of the mica flakes
Such relative 534 enrichment in Si and Al by selective depletion of other cations in phyllosilicates during biological weathering has been reported before (Boyle et al 1967; Paris et al, 1996; Wierzchos & Ascaso, 1996). 538 Using the Principal Component Analysis (PCA) analysis, a new system was generated with the principal components in which the chemical results were investigated in terms of the type of weathering induced by each fungal species
Summary
8 MPa, and can produce structural alterations of phyllosilicates (Bonneville et al, 2009), possibly by causing strain in the mineral during hyphal growth. The more restricted attention to dissolution mechanisms has resulted in a limited documentation of microscale tracks on mineral surfaces (Bonneville et al, 2009; Gazzè et al, 2012). Balogh-Brunstad et al (2008b) indicated that only 1% of the dissolution in their experiments with liquid-medium cultures took place by the generation of channels on the surface of biotite, with 99% due to global dissolution. Water saturated conditions in their experiments could be the reason for low dissolution by contact with fungal hyphae, because water and nutrient limitation probably foster direct hyphal dissolution (Hoffland et al, 2004; Balogh-Brunstad et al, 2008b). The aims of this study were first to investigate changes in the morphology and elemental composition of mica flakes using SEM-EDS and second to document the mobilization of microelements from the minerals to the mycelium. 156
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