ABSTRACT
Geomycology can be de›ned as “the scienti›c study of the roles of fungi in processes of fundamental importance to geology” in past, current, and future contexts (Gadd 2007a, 2011; Gadd et al. 2012). Important topics under this heading include bioweathering of rocks and minerals, soil formation, the transformation and accumulation of metals, and the cycling of elements and nutrients. Organic matter decomposition and degradation can also be included, since these result in major biogeochemical cycling of elements in
the biosphere, with the chemo-organotrophic metabolism of fungi determining all fungal activities and interactions with the environment. A variety of inorganic or organic fungal metabolites can serve as chemical reactants in processes such as metal immobilization or solubilization and rock and mineral bioweathering, while biomechanical effects on solid substrates result from the fungal branching ›lamentous growth form (Burford et al. 2003a; Gadd 2007a, 2008a). “Geomycology” can be considered a subset of “geomicrobiology,” namely the role of microorganisms and microbial processes in geological and geochemical processes (Ehrlich
CONTENTS
9.1 Introduction .................................................................................................................................................................121 9.2 Metal-Fungal Interactions and Transformations ....................................................................................................... 122
9.2.1 Metal Mobilization ......................................................................................................................................... 122 9.2.2 Metal Immobilization ..................................................................................................................................... 122
9.3 Bioweathering of Rocks and Minerals: Mineral Transformations ............................................................................. 123 9.3.1 Mineral Formation .......................................................................................................................................... 123 9.3.2 Mineral Biodeterioration ................................................................................................................................ 123
9.4 Common Mineral and Biomineral Transformations by Fungi ................................................................................... 124 9.4.1 Carbonates ...................................................................................................................................................... 124 9.4.2 Oxalates .......................................................................................................................................................... 124 9.4.3 Oxides ............................................................................................................................................................. 125 9.4.4 Phosphates ...................................................................................................................................................... 125 9.4.5 Silicates ........................................................................................................................................................... 126 9.4.6 Reduction or Oxidation of Metals and Metalloids ......................................................................................... 126 9.4.7 Other Mycogenic Minerals ............................................................................................................................. 126
9.5 Fungal Symbioses in Geomycology ........................................................................................................................... 126 9.5.1 Lichens ............................................................................................................................................................ 127 9.5.2 Mycorrhizas .................................................................................................................................................... 127
9.6 Environmental and Applied Signi›cance of Geomycology ....................................................................................... 127 9.7 Conclusions ................................................................................................................................................................. 129 9.8 Acknowledgments ....................................................................................................................................................... 129 References ............................................................................................................................................................................ 130
and Newman 2009; Gadd 2010). Although appreciation of fungi as agents of biogeochemical change is growing, they are frequently neglected within broader geomicrobiological contexts (Gadd 2008b). Undoubtedly, the main reason for this is the vast metabolic diversity found in archaea and bacteria, including their widespread abilities in using a variety of terminal electron acceptors in respiration and affecting many different redox transformations of metal species (Gadd 2008b; Kim and Gadd 2008). However, in aerobic terrestrial environments, fungi are of great importance, especially when considering rock surfaces, soil, and the plant root-soil interface. Free-living fungi have a major role in the decomposition of plant and other organic materials, including xenobiotics, and, therefore, in the biogeochemical cycling of all the elements associated with such substances (e.g., C, N, P, S, and metals) (Gadd 2004a, 2007a, 2008a). Fungi are also important components of rock-inhabiting microbial communities, participating in mineral dissolution and secondary mineral formation (Burford et al. 2003a,b, 2006; Fomina et al. 2005a,b; Gadd et al. 2005, 2007; Gadd 2007a). As a result of these properties, fungi can be major biodeteriorative agents of stone, wood, plaster, cement, and other building materials (Gadd et al. 2014). Mycorrhizal fungi are associated with most plant species and are involved in major redistributions of inorganic nutrients (Fomina et al. 2006; Finlay et al. 2009), while lichens, a fungal growth form, play important role in rock colonization and early stages of mineral soil formation (Haas and Purvis 2006). Free-living fungi may also have a role in the maintenance of soil structure, owing to their ›lamentous branching growth habit and exopolymer production (Ritz and Young 2004). In the aquatic environment, fungi are also important decomposers (Reitner et al. 2006; Edgcomb et al. 2011).
