Using extracellular enzymes and the nonenzymatic Fenton reaction (Eastwood et al., 2011), they are able to access nutrients in recalcitrant forms such as those bound within the lignocellulosic matrix of wood. In contrast to ECM fungi, free-living saprotrophic wood-decay fungi derive C from dead organic material. In particular, many species in the obligately ECM (Briscoe, 1959 Tedersoo et al., 2010) plant order Pinaceae are highly economically and ecologically important, as they are dominant members of forests in boreal and temperate zones (Liston et al., 2003). 2% of terrestrial plant species form this type of association (Tedersoo et al., 2010), the boreal and temperate forest biome that they dominate occupies a disproportionately large global area ECM fungi and their associated plant species thus have a significant influence on global biogeochemical cycling (Averill et al., 2014). This proliferation between root cortical cells is called a Hartig net, and is the interface across which nutrients obtained by the fungus from the soil are traded from fungus to plant in return for photosynthetically fixed carbon (C) (Smith & Read, 2008). In this association, fungi encase the root tips of host plants in a sheath of fungal material called a mantle, and proliferate in the apoplastic space between root cortical cells (Smith & Read, 2008). The ectomycorrhizal (ECM) symbiosis, involving a polyphyletic group of fungi spanning Basidiomycota, Ascomycota and Mucoromycotina (formerly Zygomycota) (Hibbett et al., 2007 Tedersoo & Smith, 2013), is widespread and has important effects on ecosystem composition and function (van der Heijden et al., 2015).
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