Soil microbial legacy determines mycorrhizal colonization and root traits of conifer seedlings during subalpine forest succession

Aim Soil microbial legacy is a potentially important regulator of the associations of plants and mycorrhizal fungi. However, our understanding of how plant performance and root-associated fungi react to distinct soil microbial legacies during subalpine forest succession remains unclear. Methods A pot experiment of two coniferous ( Picea asperata Mast. and Abies fargesii var. faxoniana (Rehder & E. H. Wilson) Tang S. Liu) tree seedlings, using sterilized soil inoculated with the soil microbial legacy of herbs, shrubs, and trees, was conducted in a greenhouse. Plant biomass, root morphological traits (total root length, root surface area, and the number of root tips), the percentage of ectomycorrhizal (EcM) root colonization, root-associated fungal communities, and soil inorganic nitrogen content were measured. Results Both coniferous seedling performance and EcM colonization were facilitated when grown in the soil microbial legacies of shrubs and trees rather than herbs. Correspondingly, soil microbial legacy favored root-associated EcM Ascomycetes and EcM fungi with ‘short-distance’ exploration type. The soil microbial legacies of trees induced a greater relative abundance of Wilcoxina, while those of herbs and shrubs resulted in greater abundances of Trichophaea , Geopora , and Hebelom a (belonging to ‘short-distance’ exploration type). Notably, the relative abundances of ‘short-distance’ explorers were positively correlated with root biomass. Conclusions Soil microbial legacy may affect tree seedling establishment and modify plant performance across successional stages by regulating the colonization, composition, and exploration type of root-associated fungi.