Intraspecific plant-soil feedback in four tropical tree species is inconsistent in a field experiment

Soil microbes can influence patterns of diversity in plant communities via plant-soil feedbacks. Intraspecific plant-soil feedbacks occur when plant genotype causes variation in soil microbial composition, resulting in differences in the performance of seedlings growing near their maternal plants versus seedlings growing near non-maternal conspecific plants. How consistently such intraspecific plant-soil feedbacks occur in natural plant communities is unclear, especially under variable field conditions. We conducted an in situ experiment with four native tree species on Barro Colorado Island (BCI), Panama. Seedlings of each species were transplanted beneath their maternal tree or another conspecific tree in the BCI forest. Mortality and growth were assessed at the end of the wet season (~4 months post-transplant) and at the end of the experiment (~7 months post-transplant). Differences in seedling performance among field treatments were inconsistent among species and eroded over time. Effects of field environment were detected at the end of the wet season in two of the species: Virola surinamensis seedlings had higher survival beneath their maternal tree than other conspecific trees, while the opposite pattern was found in Ormosia macrocalyx. However, these differences disappeared by the end of the experiment. Our results suggest that intraspecific plant-soil feedbacks may not occur consistently under field conditions in tropical tree species and may have a limited role in determining seedling performance in tropical tree communities. Future studies are needed to elucidate the environmental and genetic factors that determine the incidence and direction of intraspecific plant-soil feedbacks in plant communities.

Methods
In an in-situ field experiment on Barro Colorado Island, Panama, we collected biomass, growth, and survival data on experimental seedlings of four tropical tree species.