Soil-mediated competitive mechanisms that drive species displacement and coexistence in the Holcus invasion

Although invasive plants have been studied extensively, the specific mechanisms by which they are able to dominate a system and impact native flora remain unclear. Moreover, we lack explanatory mechanisms accounting for invasion processes that result in displacement of some native species yet coexistence with others. I explored the ecological and evolutionary effects of soil-mediated interactions in the Holcus lanatus L. (Velvetgrass) invasion of the California coastal prairie. In particular, experiments examined Holcus’ effect on soil nutrients and microbial community and subsequent effects on native plant competition. Where possible, potential variation between different portions of the active Holcus invasion were incorporated into the study. Results indicate that soil nutrients and soil microbial communities significantly differ in sites invaded by Holcus compared to uninvaded sites. When grown in soil ‘trained’ by Holcus, coexisting native species differ in growth and competitive ability in comparison to displaced native species.