Janzen-Connell patterns can be induced by fungal-driven decomposition and offset by ectomycorrhizal fungi accumulated under a closely related canopy

1. Seedlings near a conspecific adult might suffer increased mortality due to pressure from enemies such as belowground pathogenic fungi (Janzen-Connell Hypothesis), however variation exists among taxa such that some experience low levels of mortality. We hypothesized that seedlings close to adults might profit, rather than suffer, from belowground fungi, notably from mycorrhiza or decomposers, in particular near large adult trees and under a closely related canopy.
2. We planted oak seedlings in a temperate forest at different distances from adults and followed seedling mortality, budburst (early budburst permitting photosynthesis during the best light conditions) and leaf herbivory. We applied fungicide on half of the seedlings for 2 years to identify the net effect of belowground fungi on seedlings. We quantified seedling mycorrhization and fungal-driven decomposition of a neighbourhood-specific and an unspecific substrate, local oak leaves and cellulose, respectively. Finally, we r...