DISSERTATION RESEARCH: Synthesizing the Mass-ratio and Novel-trait Hypotheses to Explain Variability in the Impact of Plant Invasions on Coupled C and N Cycling

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Invasive plant species can have significant detrimental effects on ecosystem services that sustain ecosystem and human health. These impacts, however, are highly variable and hard to predict, raising difficulties for policy makers deciding how to allocate finite resources to address plant invasions. This project aims to understand factors that drive variability in the impact of one of the most widespread invasive plant species in the eastern US, Microstegium vimineum (Japanese stiltgrass) on carbon and nitrogen cycling. Specifically, the project will investigate the relative importance of two hypotheses that describe variation in invader impacts: first, that species have greater impacts where they are most abundant; and second, that species have greater impacts where they function most differently from the resident vegetation with respect to the ecosystem process of interest. Investigators will use a combination of observational studies and field manipulations to test these hypotheses, and a modeling approach to link drivers of variability in invader impacts to biogeochemical processes that control nutrient fluxes from plant litter across varying soil environments. The modeling approach will explore invader characteristics and abundances that limit or promote its impact on carbon and nitrogen cycling. By combining observational, experimental and modeling approaches, this research will provide a unique and powerful synthesis that will both inform the management of this species and address key questions of basic ecological interest.Determining the role that individual species play in controlling ecosystem processes is one of ecology?s grand challenges as global distribution of organisms shift due to human activity. This project addresses how individual invasive plant species can impact critical ecosystem processes that have a strong influence on global climate, soil fertility, ecosystem productivity, and ecosystem resilience. This research will produce novel information on how the impacts of non-native species invasions on ecosystem functions are mediated by the individual and interactive effects of coexisting species. Such information will improve general theory on consequences and mechanisms of non-native species invasions under different conditions, and will advance our ability to predict when and where biological invasions will have the greatest effects. This research will result in broader impacts in three key areas. First, the project will provide excellent experience and broad training for an undergraduate student each academic year of the project and will substantially improve a PhD student?s research. Second, the PIs will disseminate their research findings to land managers, other ecologists, and the general public through a web site, web blog, public presentations, and publications. Third, the project will provide important information for predicting where and under what conditions invasive species will have the greatest impacts. Specifically, the focal species, Microstegium, is one of the most common invasive plants in eastern deciduous forests where it has significant community and ecosystem impacts. Improving the ability of land managers to efficiently target invasive removal and restoration efforts will greatly enhance conservation and management efforts in the eastern U.S.