This study illustrates the important role of soil fungi in tree population dynamics of temperate forests. In general, when a particular plant species dominates an area of land, it attracts species that feed on it. In an experiment conducted in this study, the roots of surviving seedlings had 60% fewer lesions when they were planted beneath a tree species different than their own, compared to when they were planted beneath a member of their own species, “potentially because of increased root damage by antagonists” [Bennett 2017: 2].
However, seedlings inoculated by ectomycorrhizal (EM) fungi, which forms a protective sheath around its host’s roots and also efficiently transferring nitrogen to its host,
had 840% higher survival and 75% lower lesion densities than those of uninoculated seedlings when planted beneath conspecifics [members of the same species], but inoculation had no effect beneath heterospecifics [members of another species]. In contrast, AM seedlings did not benefit from pre-inoculation, nor did pre-inoculation affect lesion densities, regardless of transplant location [Bennett 2017: 2].
Mycorrhizal fungi colonize plant roots, where they transfer nutrients to hosts in exchange for sugar produced through photosynthesis. Ectomycorrhizal fungi form a sheath around tree roots, while arbuscular mycorrhizal (AM) fungi colonize tree roots by penetrating root cell walls. In this study, as noted above, trees with EM fungi symbionts appear to be better protected from pathogens than are AM trees when growing amongst others of their own species. This dynamic affects the population dynamics of the forest by facilitating larger stands of EM trees, while inhibiting the clustering of AM trees.
In summary, “These results suggest that mycorrhizal type, through effects on plant-soil feedbacks, could be an important contributor to population regulation and community structure in temperate forests” [Bennett 2017: 1].