Tree diversity modifies distance-dependent effects on seedling emergence but not plant-soil feedbacks of temperate trees

摘要

Negative plant-soil feedbacks can impair seedling survival near conspecific trees and may enhance forest diversity. However, the reciprocal aspect of this relationship, the influence of tree diversity on the strengths of plant-soil feedbacks is unknown. We examined whether tree diversity can affect plant-soil feedbacks of two common temperate tree species, beech (Fagus sylvatica) and sessile oak (Quercus petraea). Soils were collected from adjacent to beech and oak trees growing in a manipulative tree diversity field experiment and used as inocula in a greenhouse experiment to determine whether increasing tree diversity could moderate the strengths of plant-soil feedbacks. We also compared plant-soil feedback responses between Q. petraea and F. sylvatica to test the hypothesis that stronger negative feedbacks contribute to the relative rarity of Q. petraea. Negative plant-soil feedbacks on seedling emergence were observed for both tree species. Emergence increased with increasing distance of the soil inocula from established trees in the field, but only for inocula taken from the low-diversity treatment (monocultures) and irrespective of the inoculum source (i.e., from conspecific vs. heterospecific trees). In contrast, tree diversity had no influence on the biomass responses of seedlings for either tree species. Quercus petraea seedlings experienced negative plant-soil feedbacks in their biomass responses which cascaded up to higher trophic levels, i.e., leaf pathogen infection. Fagus sylvatica biomass responses suggested positive plant-soil feedbacks, supporting the hypothesis that the abundance of this species is less limited by interactions with natural enemies. Our results suggest that distance-dependent seedling emergence in temperate forests may depend on the diversity of tree communities and that plant-soil feedbacks may cascade up to higher trophic levels and change with the life history stage of the seedlings involved. An increased focus on the surrounding communities would help to judge the importance and context-dependency of plant-soil feedbacks as a mechanism for stabilizing forest diversity.