DISSERTATION RESEARCH: The role of rhizobial mutualisms in the establishment and colonization of non-native acacia species in California

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Plants that harbor nitrogen-fixing bacteria, such as alfalfa and soybean, are an important natural source of soil fertility. The bacteria also increase the growth of their host plants, and some wild plants with N-fixing bacteria become highly invasive; they spread and crowd out other species when introduced by humans to a new region. This project will test the hypothesis that the invasiveness of these introduced plants is determined by their ability to form relationships with the N-fixing bacteria in their new habitats, or by whether their own N-fixing bacteria have been introduced along with them. Researchers will compare the species of trees and shrubs in the genus Acacia that have been introduced to California from Australia. Some of these species have spread widely, while others have not become invasive. The project will use molecular genetic techniques to distinguish native, Californian, N-fixing bacteria from introduced, Australian bacteria, and test whether the more invasive species are more able to harbor Californian bacteria, have more Australian bacteria, or depend less upon N-fixing bacteria for their own growth.Australian Acacias have become invasive in the U.S. and around the world, threatening agricultural lands and areas of conservation concern, and reducing water supplies. Results from this project will help managers control the spread of these trees and of other N-fixing, invasive plants. Researchers will actively disseminate results to habitat restoration programs near San Francisco and San Diego. The project will also train a Ph.D. student and two undergraduates and develop presentations for K-12 students in Louisiana.