Nanoscale investigation of mineral surface dissolution and the organic-inorganic interface: implications for geology and the environment

This area of work investigates the nanoscale interaction between a biological organism and an inorganic surface. Fungal hyphae, the filamentous “roots” of fungi exist in symbiosis with tree roots, play a key role in breaking down the crystal structure of minerals and liberating the essential nutrients therein, e.g. calcium, potassium, phosphorous. This “first contact” between rock and plant is therefore of utmost importance for the environment, as it is at this interface that soil formation begins, and where carbon dioxide is taken in by the tree and utilised and deposited in the root system. The fungi are known to exude a variety of chemicals, including organic acids such as acetic acid, which can attack mineral surfaces, but the mechanisms and modes of action are not fully understood.

Using model mineral systems, such as mica, chlorite and hornblende, which may be cleaved to produce atomically-flat surfaces, we have studied the effects of the fungi on the mineral surface. There are two regimes of experimental study: (1) at the mesoscale, the controlled growth of fungi on surfaces, with imaging of the effects, and use of other nanoscale characterization techniques such as X-ray Photoelectron Spectroscopy to analyze the exudates and surface modifications; and (2) at the nanoscale, studies of surface dissolution morphology and kinetics in model experiments with single-, double- and complex-component mixtures of surface-active chemicals. The work takes full advantage of the interdisciplinary Nano group and involves interaction with geochemists and biologists in order to get a full understanding of the organic-inorganic interface.

Nanoscale dissolution of biotite. Etch pit evolution in a time interval of 13 min. Three triangular etch pits are present in (a), which expand and coalesce maintaining the triangular shape (b, c). Two initially rounded etch pits in (a) convert to a triangular form (b, c) through preferential expansion along three edges, indicated by arrows in (a) and (c). Z ranges: 0-5nm (a, b), 0-6nm (c).

A microcosm of the fungus Suillus bovinus in association with Scot's Pine seeding. It is evident how the fungal mat (white filaments) greatly enhances surface exploration compared to only plant roots alone.

Recent highlights

  • First observations and measurement of (001) surface ligand-promoted dissolution activation energy for biotite
    Haward, S. J.; Smits, M. M.; Ragnarsdottir, K. V.; Leake, J. R.; Banwart, S. A.; McMaster, T. J., In situ AFM measurements of biotite basal plane reactivity in the presence of oxalic acid. Geochimica et Cosmochimica Acta 2011, 75 (22), 6870-6881.
  • First AFM evidence for fungal-mediated weathering of hornblende
    Saccone, L., Gazzè, S. A., Duran, A. L., Leake, J. R., Banwart, S. B., Ragnarsdottir, K. V., Smits, M. M., McMaster, T. J., High resolution characterization of ectomycorrhizal fungal-mineral interactions in axenic microcosm experiments. Biogeochemistry 2011, Published Online November 2011 doi: 10.1007/s10533-011-9667-y.
  • Observation of nanochannels on chlorite
    Gazzè, S. A., Saccone, L., …and McMaster, T. J. The bio-inorganic interface: the interaction of ectomycorrhizal hyphae with phyllosilicate minerals. Journal of Geophysical Research 2012, Submitted for publication.
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