Spatial ecology of ectomycorrhizal fungal communities

Ectomycorrhizal (ECM) fungi evolved recently (about 150 million years ago), in many separate events, from saprotrophic fungi (brown"rot, white"rot and litter decaying) (Hibbett et al., 2000; Wang and Qiu, 2006; Tedersoo et al., 2010a; Kohler et al., 2015). Their importance to host carbon and nutrient cycling has been well documented (Smith and Read, 2008), but remains an area of fruitful research. ECM fungi associate with approximately 2% of known plant species, but those species tend to be large, woody, and dominant members of global ecosystems (Brundrett, 2009). Although research on ECM systems has typically focused on northern hemisphere temperate and boreal forests, the symbiosis is widespread, occurring in arctic, tundra, Mediterranean and tropical ecosystems as a result of biogeographical processes (Taylor and Alexander, 2005) and, in some cases, human intervention (e.g., Hayward et al., 2014). Physiologically, ECM fungi form structures that exist along a gradient from the microscopic (e.g., spores, individual hyphae, Hartig net) to the macroscopic (e.g., clusters of ECM root tips, tubercules, rhizomorphs, mycelial networks and sporocarps; Smith and Read, 2008). Thus, due to their biology, they have the potential to display multiple levels of spatial organization simultaneously. Understanding these different levels of organization, and how ECM fungi interact with their hosts, the soil environment, and other trophic groups, is key to making inferences about their biology and their impact on ecosystem"level ecological processes.