Understanding the ecosystem-level effects of stiltgrass: does it set the stage for its own success?
Justin Wright, Duke University

Understanding the ecosystem-level effects of stiltgrass: does it set the stage for its own success?

Plant secondary compounds frequently play an important role in plant invasions by influencing interactions between invading plants and other components of the ecosystem including herbivores, soil microbes, and competitors. Microstegium has been documented to have effects on a number of aspects of the ecosystem that are surprising given its physiology and life history, and may point to the presence of unusual secondary chemistry. This talk brings together evidence from the published literature with data from research currently in progress to evaluate the hypothesis that the ecosystem-level effects of Microstegium may be due to its secondary chemistry. First, we show that while Microstegium shows low rates of herbivory compared to co-existing native vegetation, this level of herbivory is not significantly lower than other native grasses. Combined with recent papers showing significant herbivory and fungal pathogens on Microstegium, we conclude that if Microstegium contains secondary compounds, they are insufficient to prevent consumption by native organisms. Secondly we evaluate the effects of leaf extracts of Microstegium on the functioning of soil microbial communities. Consistent with previous studies, we find that Microstegium appears to alter the function of soil communities, but that the effects of secondary chemistry in the leaf leachate seemed to be less important than whole-plant effects. Finally, we follow-up on a recent study showing that leaf-leachate from Microstegium significantly reduces germination in radish seeds by testing the effects of Microstegium on germination rates of tree seedlings. We find that leaf-extracts do have significant effects on the germination and growth rates of some, but not all tree species. We argue that further study of Microstegium’s secondary chemistry, including identifying particular chemicals present and determining what factors affect the production of secondary compounds will be a productive route for understanding some of the intriguing ecosystem-level impacts of this invasive species.