Symbiotic associations such as those observed between many plants and soil bacteria are key players in the success or failure of a newly introduced species to its non-native habitat. However, such interactions are often categorized as fixed and unchanging factors working similarly and predictably across populations and varying environmental conditions. Species interactions are often dependent on the environment in which they occur. The Mitigation-Exacerbation Continuum recognizes that the relationships between plant hosts and their microbiota can be far more complex than this, shifting from either parasitic to mutualistic taxa in the presence of stress. For example, bacteria in the soil may increase plant invasion success by mediating or reducing the effects of stress on its host. Conversely, they could decrease invasion success by exacerbating or worsening the pressures of a stressful environment. This study aims to test the predictions laid out by this novel framework using native and invasive populations of a widely distributed legume species, Medicago polymorpha, and its most common rhizobia symbionts. To do this, we conducted a greenhouse study that manipulates plant genotype, rhizobia presence, and local nutrient environment to test host-microbe interactions across a range of benign, intermediate, and stressful conditions.
Results/Conclusions
Plants grown in the greenhouse study showed signs of variation across genotypes. Overall, the invasive range plants had higher growth and fruit production, relative to native range plants. Genotypes also displayed variable responses to nutrient environments in terms of size and fitness. The results from this study help fill in the gaps of knowledge we currently possess in regard to the function, stability, and invasive potential of many plant communities. Moreover, the results from this experiment could have great implications for controlling the spread of invasive species that escape from agriculture into surrounding natural communities more effectively.
