In tropical monodominant forests, ectomycorrhizal adult trees are hypothesized to support high conspecific seedling survival through their ectomycorrhizal fungi. However, we found that seedling share only half of their ectomycorrhizal fungi with conspecific adults, harbor a large portion of previously undescribed ectomycorrhizal fungal taxa, and their fungal communities become more dissimilar over time to those on sympatric adult trees. Seedlings may not depend on support from local adults as much as previously thought.
Ectomycorrhizal tree species may benefit from positive plant–soil feedbacks, where soil environments near adult trees enhance conspecific seedling growth and survival. In tropical monodominant forests, seedling survival is particularly important, as seedling banks help maintain stand-level dominance over generations. Positive plant–soil feedbacks may be mediated by diverse ectomycorrhizal fungal communities, which improve nutrient acquisition of heavily shaded seedlings. Despite the potential importance of these fungi, little is known about ectomycorrhizal fungal community development on seedlings of tropical monodominant trees. In Guyana, we sequentially monitored percent colonization and species composition of ectomycorrhizal fungi on an even-age cohort of seedlings of the tropical monodominant tree Dicymbe corymbosa (Fabaceae subfamily Detarioideae). Ectomycorrhizal fungi found on D. corymbosa seedlings over a 12-month period of early development were compared to those of conspecific adults and four other ectomycorrhizal tree species in the region. Species turnover was high (80%) between 6- and 12-month-old seedlings, though the /russula-lactarius, /clavulina, and /tomentella-thelephora lineages were species-rich on seedlings at all ages. The number of ectomycorrhizal morphotypes per seedling increased with age, but extent of fungal colonization did not. Seedling ectomycorrhizal fungi were shared with sympatric conspecific adults (55%) and, to a lesser extent, regional heterospecific adults (27%), but numerous species were previously unrecorded for Guyana. Over their development D. corymbosa seedlings did not rely strictly on adult trees for their mycobionts but appeared to foster unique assemblages of ectomycorrhizal fungi.