Nitrogen-Fixing Plants and Invasions: A Mechanistic Approach to Community Impacts

Abstract

Biological invasions are a major component of global environmental change, with widespread and often unpredictable impacts on natural systems. Invasive nitrogen-fixing plants are particularly compelling in this context because they can alter the availability of a key limiting resource—nitrogen—thereby changing the conditions under which plant species interact in invaded systems. These species have the potential to reshape ecological interactions by modifying the resource environment that structures them. In this thesis, I synthesize existing literature to examine how invasive nitrogen-fixing plants influence plant communities, focusing on plant–plant interactions underlying changes in biodiversity, density, and species composition. I categorize the primary facilitative and competitive interactions that emerge following nitrogen enrichment by invasive nitrogen-fixing species, and then extend this approach by considering how these interactions co-occur within invaded communities. Across studies, the balance of facilitation and competition often shifts depending on environmental context, invader abundance, recipient community composition, and stage of invasion. I further explore how these invasion-associated interactions intersect with successional processes, highlighting potential avenues for how the effects of invasive nitrogen-fixers may change as communities develop over time. Overall, this synthesis shows that community-level impacts of invasive nitrogen-fixing plants are best understood as the outcome of multiple, interacting processes.