Ontogenetic Shifts in Mycorrhiza-Mediated Neighborhood Effects Among Multi-Stemmed Species in a Subtropical Forest

Although plant–mycorrhizal fungi associations play critical roles in maintaining species diversity within forest communities, the influence of tree ontogeny in mediating these effects on species diversity remains poorly understood. In this study, we integrated tree census data with information on the mycorrhizal types and sprouting ability of multi-stemmed species from a subtropical forest to assess how mycorrhiza-mediated neighborhood interactions affecting survival vary across ontogenetic stages (sapling, juvenile and adult stages) and how these effects correlate with sprouting ability. Our results revealed pervasive ontogenetic shifts in mycorrhiza-mediated neighborhood effects on tree survival for multi-stemmed species. AM heterospecific neighbors consistently exerted positive effects on tree survival across all life stages. In contrast, ErM heterospecific neighbors significantly influenced survival only at the sapling stage, whereas EcM heterospecific neighbors had significant effects during the juvenile and adult stages. When focal individuals were classified by mycorrhizal type, AM focal plants were significantly influenced by three types of mycorrhizal heterospecific neighbors, with the effect of AM heterospecific neighbors at the sapling stage being significantly greater than those of EcM or ErM heterospecific neighbors. Notably, AM heterospecific neighbors were critical predictors of survival for EcM focal plants during both the juvenile and adult stages, while AM and EcM heterospecific neighbors jointly the enhanced survival of ErM focal plants during the adult stage. Moreover, the effects of both AM and EcM heterospecific neighbors increased significantly with the sprouting ability of multi-stemmed species, particularly at the sapling stage. Our study highlights the importance of incorporating tree ontogeny and mycorrhizal symbiosis types into the assessment of factors contributing to species coexistence among long-lived organisms.