Extraradical mycelium (ERM)
The extraradical mycelium (ERM) is composed of two types of hyphae: unbranched runner hyphae, which run parallel to the root length to initiate secondary colonization, and highly branched absorptive hyphae responsible for nutrient uptake from the soil and subsequent translocation to the host (Friese & Allen, 1991). (Bago et al. , 1998a) and Dodd et al. (2000) observed the formation of ’branched absorbing structures’ - small groups of dichotomous hyphae - within the ERM in species of Glomeraceae. The ERM is also accountable for the formation of spores and auxiliary cells in the soil. Phenotypic variables associated with the ERM, such as hyphal length and density, interconnectedness, and hyphal diameter, have been studied in some AM fungal species (Dodd et al. , 2000; Avio et al. , 2006). The extraradical mycelium can form Common Mycorrhizal Networks (CMNs), where a single AM fungus associates with multiple plant hosts, interconnecting them within a shared mycelial network. These networks may serve as biological bridges, facilitating resource exchange and, possibly, communication among different plant hosts (Barto et al. , 2011; Babikova et al. , 2013). However, more research is needed to determine the role of CMNs in natural environments and to what extent the capacity to form CMNs can be considered a fungal trait (Karstet al. , 2023).