Recruitment & Plant-Soil Feedback: The Effects of Mature Trees on Seedling Survival

Abstract

Plant-soil feedbacks (PSFs) are mechanisms by which plants alter the structure, chemistry, and biology of soil which then influences plant survival. Over time, PSFs have the ability to alter forest composition because the soil biota associated with adult trees differentially affects the establishment of conspecific or heterospecific seedlings. Greenhouse studies have shown that host-preferred pathogens act as a type of PSF that can potentially infect different species of seedlings. We conducted a field study over two summers comparing the survival of four seedling species underneath three adult tree species in a temperate forest. We applied fungicide to the soil surrounding half of the seedlings in order to exclude the most common fungal pathogens. We found that initial stem height and soil moisture significantly influenced seedling survival for all species. Possibly due to unusually extreme drought, we observed great variability in survival rates, and so we found no statistically significant differences between our test and control groups. However, we were able to quantify the effects of the pathogenic fungal community associated with specific tree canopies on the survival of conspecific and heterospecific seedlings. We found indications of conspecific seedling-canopy species interaction which affected survival, although this varied among species. Prunus serotina seedlings treated with fungicide experienced a ~92% increase over the average survival of seedlings under control conditions. Comparisons found that under control conditions, all seedling species were negatively affected by the fungal communities associated with P. serotina canopies except for E. umbellata. Conversely, fungal communities associated with A. saccharum canopies tended to have the weakest affect for all native species. Overall, we found that 2 seedlings treated with fungicide tended to experience increased survival, though the relative degree of effects varied. In summary we did not observe strong changes in PSF effects between treatments of conspecific canopies on seedlings survival but we were able to detect differential survival probabilities due to the fungal community which may contribute to the coexistence of these species.