Dissertation Research: Constraints on Invasion by a Nitrogen-fixing Woody Shrub and Consequences for Resident Grassland Species

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0073068D'AntonioInvasions by wood shrubs (particularly those that fix nitrogen) into grasslands have received much attention, yet we do not understand the role that N-fixation plays in the invasion process. In particular, we do not know what constraints may be imposed by soil-borne mutualists on fixation efficiency, nor the degree to which nutrient limitation of the resident community contributes to the competitive advantage of N-fixation. This research will investigate three questions that address constraints on a nitrogen-fixing shrub's ability to invade a coastal California grassland habitat, and the consequences of that fixation for resident species interactions: (1) How does the success of colonization by broom into grassland habitat change with nutrient limitation of the resident species? (2) How does availability or quality of Rhizobium innoculum affect this species" ability to invade and fix nitrogen? (3) How does enrichment of soil by N-fixation affect species interactions? Coastal California grasslands offer an ideal opportunity to perform this research because they lack a significant native N-fixing component, are themselves nitrogen limited, and are currently experiencing dramatic invasions by several introduced N-fixing shrubs.