The Janzen-Connell hypothesis proposes that host-specific natural enemies could maintain high tree species diversity by reducing seedling survivorship near conspecific adults and/or at high conspecific seedling densities. Negative feedback between plant and soil communities could be an important mechanism of such non-competitive distance and density-dependent (NCDD) mortality. In a greenhouse experiment, we assessed: 1) lifespan and growth responses of Acer rubrum, Acer saccharum, Fraxinus americana and Quercus rubra seedlings to extracts taken from soils that had been cultured by adults of each of these species; 2) whether these relationships were influenced by the species and density of seedlings culturing the soil prior to extraction; 3) host-specific soil pathogens as the mechanism creating these plant-soil feedbacks; and 4) whether low light availability increased species vulnerability to these pathogens.
Results/Conclusions
Species-specific feedbacks between adult trees (but not seedlings) and the soil influenced lifespan and/or growth for all species, but contrary to the Janzen-Connell hypothesis, not all species benefited from escaping conspecific cultured sites. Instead seedlings for some tree species were harmed more in soils cultured by heterospecifics than conspecifics. For instance, F.