ABSTRACT
Ectomycorrhizae (ECM), mutualistic associations between tree roots and fungal hyphae, play a pivotal role in nutrient and carbon cycling in forest soils. Ectomycorrhizal fungi absorb essential nutrients and supply them to the tree in exchange for photosynthetic carbohydrates. Approximately 70% of all phosphorus and nitrogen that a tree needs are collected and supplied by ECM fungi in return for approximately 20% of the carbon that it photoassimilates. Ectomycorrhizal fungi can be found in several lineages of the fungal tree of life; they have no common ancestor and form a polyphyletic assemblage of fungi. Molecular phylogenetic and identi›cation studies suggest that the ECM symbiosis has arisen independently from humus and wood saprotrophic ancestors and persisted at least 66 times in fungi (Tedersoo et al. 2010). Pinaceae are the oldest extant plant family symbiotic with ECM fungi. Several fungal orders and families that contain ECM species are at least the same age (≈160 Ma), suggesting the oldest origin of ECM at this point (Hibbett and Matheny 2009). Currently, the ECM symbiosis can be found in different types of environments and dominates boreal, temperate, Mediterranean,
and subtropical forests and woodlands (Read and PerezMoreno 2003). Almost all trees need to establish this symbiotic relationship with one or more fungal species to promote their growth and reproduction, to be competitive, and to increase their ecological ›tness.
