Growing awareness of the substantial loss of native forests has spurred exploration of diverse forest regeneration practices. Conventional restoration efforts have focused on the active or passive recovery of aboveground communities, aiming to reestablish essential forest functions.　However, insufficient knowledge of how diverse forest organisms underpin multiple ecosystem functions constrains mechanism-based assessments of forest restoration. In particular, despite their ecological importance, little is known about the association of soil microbes with ecosystem functions during long-term forest development. Here, we aim to understand how soil microbial communities associate with forest functional recovery, especially under different restoration strategies.
　This study focused on the long-term response of the ecosystem over a 50-year chronosequence to two restoration methods in Hokkaido, Japan: monoculture planting and natural regeneration, using old-growth forests as a reference. In addition to plant communities, we analyzed soil bacterial and fungal communities using DNA metabarcoding, as these functionally important microbial groups differ in their life-history traits. We explored ecosystem multifunctionality by considering crucial ecosystem functions like nutrient cycling, decomposition, and below-ground production during two types of forest succession.
　Forest multifunctionality recovered with forest growth, and it tended to be higher in naturally regenerated forests than in plantations after 40 years. We further demonstrated that recovery of multiple functions is required for higher biodiversity as well as aboveground and belowground species identity. Importantly, soil fungal communities were strongly associated with ecosystem multifunctionality, and their community assembly was largely explained by other taxonomic groups, including plants and bacteria. We aim to discuss how insights from community assembly can improve our understanding of biodiversity–ecosystem functioning (BEF) relationships in natural systems and provide implications for forest restoration.