Arbutus menziesii (Ericaceae) facilitates regeneration dynamics in mixed evergreen forests by promoting mycorrhizal fungal diversity and host connectivity

• Premise of study: In the mixed evergreen forests in the western United States, Arbutus menziesii is able to quickly resprout following disturbance and, as such, act as a nurse tree during forest regeneration. The mechanism for this nurse tree effect has frequently been ascribed to mycorrhizal fungi, but no detailed molecular-based studies of the mycorrhizal fungal communities associated with A. menziesii roots have yet been conducted. • Methods: We examined the structure of the mycorrhizal fungal communities associated with A. menziesii in varying forest types and seasons and assessed the potential for common mycelial networks between A. menziesii and Pinaceae hosts, particularly Pseudotsuga menziesii. Study sites were located in the Klamath-Siskyou region in southern Oregon, United States. Molecular approaches were used to identify the mycorrhizal fungi (ITS rDNA) and plant hosts (trnL cDNA). • Key results: Arbutus menziesii hosts a highly diverse mycorrhizal fungal community with similar composition to communities found on other angiosperm and Pinaceae hosts. Phylogenetic analyses of the mycorrhizal genus Piloderma revealed that host species and geographic location had little effect on fungal taxon relatedness. Multihost fungal taxa were significantly more frequent and abundant than single-host fungal taxa, and there was high potential for the formation of common mycelial networks with P. menziesii. • Conclusions: Our results suggest A. menziesii is a major hub of mycorrhizal fungal diversity and connectivity in mixed evergreen forests and plays an important role in forest regeneration by enhancing belowground resilience to disturbance.