Intraspecific negative feedback effects, where performance is reduced on soils conditioned by conspecifics, are widely documented in plant communities. However, the effect of environmental conditions on these feedbacks is rarely investigated and specifically the role of soil fertility on theses feedbacks is poorly understood. Plant-soil feedbacks are an important I hypothesized that site fertility may influence the strength and type of plant-soil feedback experienced by tree seedlings. In addition, my goal for this project was to also investigate correlations between feedback effects and nutrient suppply rates. I conducted a 10 week long greenhouse experiment where I assessed survivorship of black cherry (Prunus serotina) growing in low (~1% full sun) vs. high (~18% full sun) light availability and in non-sterile vs. sterile soils collected under the canopy of conspecific vs. heterospecific adult trees at five sites in Manistee National Forest, Michigan, USA that vary in nutrient availability. All sites are similarly aged and geographically close with their soil fertility associated with particular glacial landforms (with lowest resource conditions at outwash sites and maximum resource availability on moraines).
Results/Conclusions
I found that when seedlings were grown at low light conditions they had lower survival in their own soil in outwash and ice contacts sites associated with low fertility, but actually did better in their own soil at moraine sites associated with higher fertility. In high light conditions, the strength and whether the feedback was negative or positive varied among sites, but with no discernable pattern. When analyzing our results for the survival of black cherry seedlings in low light with the nutrient supply rates from PRS™-probes, I found a strong negative correlation between PSF and iron content in the soil and a positive correlation between PSF and cadmium, with black cherry experiencing lower survival in their own soil at sites with higher iron and lower cadmium content. In high light conditions, black cherry appeared to have lower seedling survival in their own soil at sites with higher lead and aluminum levels. These results will help determine which site factors may be significant in controlling the strength and direction of feedbacks tree seedlings experience in soils under parent trees which is important since these feedbacks can be a mechanism for maintaining species diversity in forest communities.