Interactions between Plants and Microbes: A Mechanism for Invasion of Exotic Grasses in
California?
Michelle Y. Chang
Mentor: Katharine N. Suding
The intent of this study was to detect plant-microbial feedbacks occurring in a grassland
community of exotic and native patches. The mechanisms of how exotic plants invade native
ecosystems have long been studied. Yet scientists have just begun to study microbial factors that
may facilitate invasion through plant-microbial feedbacks. In Southern California, patches of
native perennial grasses have persisted despite widespread invasion of annual exotic grasses. We
investigated plant-microbial feedbacks in favor of natives as a potential mechanism of resistance
to invasion, as well as the effects of increased nitrogen and/or drought. We grew two exotic
annual grasses, Bromus diandrus and Hordeum murinum and a native perennial grass, Nassella
pulchra in soils inoculated with microbial community from their “home” soil and in soils
inoculated with microbes from “foreign” soil in ambient, nitrogen, and drought conditions. We
found negative feedbacks in N. pulchra and B. diandrus, but no effect on H. murinum. With
nitrogen, N. pulchra did significantly better in home inoculated soils than in foreign soils, which
may suggest that N-deposition aids natives in resisting invasions. Drought caused no effect
across species, indicating that drought may negate plant-microbial feedbacks. These findings
suggest that not only are biotic plant-microbial feedbacks present and affected by drought and
nitrogen, but that feedbacks are species specific.