Do fungal pathogens follow the Janzen-Connell hypothesis?

Background/Question/Methods

The Janzen-Connell hypothesis predicts that the high biodiversity in tropical forests is explained by the strong filter created by herbivores and plant-pathogens in the establishment of conspecific seedlings. However, recent studies have also indicated that tropical tree species may vary in their susceptibility to Janzen-Connell dynamics, but the mechanisms that cause this variation are poorly understood. Protium (Burseraceae) is a genus with high richness and abundance in the tropical Americas, especially in Amazonia. Protium species develop a great diversity of chemical compounds in their leaves that have demonstrated –most of them—to repel herbivores. We investigated the links between root specialized metabolites and the colonization of belowground pathogens. We sampled roots from 20 seedlings of the 31 species of Protium in the Reserve Allpahuallo-Mishana, Iquitos, Peru. From every seedling we split the roots in two for parallel analysis of fungal communities and secondary metabolite characterization. Fungal communities were characterized by DNA extraction and amplification of the ITS2 region of the nuclear ribosomal RNA operon. Low molecular weight metabolites were analyzed using GCMS and untargeted metabolomic approaches. Additionally, total phenolic and saponin root contents was quantified.

Results/Conclusions

Preliminary results indicate a high diversity of fungi associated with the roots of individual species, with high variability both within and across species. This is matched by similarly high diversity and variability in composition of secondary metabolites. While our analyses are still in process, our predictions are that (a) we will find a negative correlation between higher metabolite diversity and the abundance of fungal pathogens; and (b) that secondary metabolite diversity will positively correlate with local abundance of individual tree species.