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). The data indicate that the capacity for facultative biotrophic relationships in free-living saprotrophic basidiomycetes may be greater than previously supposed.These features suggest the possibility of an active functional symbiosis between fungus and plant. Two fungal species showed formation of a mantle and one showed Hartig net-like structures. Thirty-four (16.9%) of the tested fungal species colonized the roots of at least one tree species.Microtome sectioning, differential staining and fluorescence microscopy were used to visualize patterns of root colonization in microcosm systems containing Picea abies or Pinus sylvestris seedlings and each saprotrophic fungus.

In order to determine the extent of biotrophic capacity in saprotrophic wood-decay fungi and which systems may be useful models, we investigated the colonization of conifer seedling roots in vitro using an array of 201 basidiomycete wood-decay fungi.ECM fungi have the capacity to decompose organic matter, and although there is increasing evidence that some saprotrophic fungi exhibit the capacity to enter into facultative biotrophic relationships with plant roots without causing disease symptoms, this subject is still not well studied. Ectomycorrhizal (ECM) symbioses have evolved a minimum of 78 times independently from saprotrophic lineages, indicating the potential for functional overlap between ECM and saprotrophic fungi.

Define microcosm