Forest diversity and plant-soil feedback: The effects of mature trees on seedling survival

Background/Question/Methods

Plant-soil feedbacks (PSFs) are mechanisms by which plants alter the structure, chemistry, and biology of soil and then subsequently influence plant survival and growth. PSFs also have the ability to alter forest composition because the PSFs associated with adult trees could differentially affect the establishment of conspecific (same species) or heterospecific (different species) seedlings. PSFs are facilitated by a variety of microbiota functioning beneficially or deleteriously. One type of PSF is performed by soil fungal pathogens. However, heterospecific seedlings can remain unaffected allowing for the establishment of different species. We seek to answer three main questions: Is seedling survivorship affected by conspecific canopy species-specific soil pathogens?, What are the effects of heterospecific adults?, and what is the relative degree of effect soil pathogens have which may influcen seedling survival accross different species?We conducted a multi-faceted field study in southeastern Michigan last summer comparing seedling mortality under five types of adult tree species which are dominant members of temperate forests. Half of the seedlings were treated with fungicide that excluded specific soil fungal pathogens.

Results/Conclusions

Results indicate that some species of seedlings treated with fungicide survived better under heterospecific adult trees than others when treated with water. For other species, survivorship was higher when fungicide was applied depending on the canopy species. Alternatively, other seedlings experienced higher mortality under conspecific adult trees when treated with fungicide. One seedling species, Quercus rubra (QuRu), experienced increased survivorship under conspecific canopies as well as certain heterospecific canopies such as AcSa when treated. However, QuRu seedlings decreased survivorship under Prunus serotina (PrSe) and QuVe canopies under treatment. Another seedling species, Lariodendron tulipifera (LiTu), expressed a change of survivorship when treated with fungicide. LiTu seedlings under control treatments had greater mortality under Quercus velutina (QuVe) and Q. alba (QuAl) canopies. However, LiTu survivorship increased when fungicide was applied. Control LiTu seedling experienced improved survivorship under Acer saccharum (AcSa) canopies. However, when treated with fungicide, LiTu seedlings under AcSa canopies express significant mortality. These trends suggest that the effect of fungal pathogens may influence tree species diversity and spatial dynamics as they relate to seedling mortality under conspecific /heterospecific fungal pathogens. Thus, pathogenic PSFs may have the potential to shape future forests. This study will help to increase understanding of the impacts of PSFs if we are to predict forest response to human disturbance, invasive species, and climate change.