Roles of pathogens on replacement of tree seedlings in heterogeneous light environments in a temperate forest: a reciprocal seed sowing experiment

In forest communities, the Janzen–Connell (J-C) hypothesis proposes that species diversity is maintained by non-competitive distance- and/or density-dependent seedling mortality caused by host-specific natural enemies. However, the effects of pathogen associations from nearby conspecifics versus heterospecifics remain unknown in spatially heterogeneous light environments. Seeds of hardwood species Cornus controversa (Cornus) and Prunus grayana (Prunus) were sown beneath 6–7 Cornus and Prunus adults in both the forest understory (FU) and in gaps (Gap) created by felling all woody vegetation near the focal adults. Seedling growth, mortality, killing agents (e.g. pathogens that cause damping-off and leaf diseases), and root infection by arbuscular mycorrhizal fungi (AMF) were investigated. We found strong habitat effects on the expression of soil fungi beneath both tree species. Seedling mortality caused by soil-borne damping-off pathogens was greater in FU than in Gap, and AMF infection, ...