Date of Award


Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biochemistry and Molecular Biology


Mary E. Rumpho

Second Committee Member

Seanna Annis

Third Committee Member

Ahmed Moustafa


Microbial symbiosis affects many aspects of the growth, development, and population structure of organisms on Earth, and has significant implications with regard to plant invasions. Invasive plants cause environmental damage by reducing native species biodiversity, altering habitats, and modifying ecosystem dynamics. Berberis thunbergii DC., a native of Japan, is an invasive plant in parts of North America. The invasive behavior of B. thunbergii in North America is the result of its popularity as an ornamental plant and the ecosystem changes induced upon plant introduction that are characteristic of microbial feedback enhanced growth and fitness. The objectives of this research were focused on studying the interactions between invasive plants and humans, above-ground plant-insect interactions, and plant-microbe interactions in the rhizosphere. A survey of the Maine landscape and nursery industry was used to assess local human contributions to the plant invasion. Microbes involved in growth, development, and population structure of a phytophagous seed predator, Rhagoletis meigenii L. (Diptera: Tephritidae) were investigated. Evidence suggests Proteobacteria are the key microbes that influence plant interactions with R. meigenii. The microbial diversity in the soil ! iii! beneath B. thunbergii was also assessed to characterize the microbes that are likely to have direct interactions with these plants in the native and invaded regions. A high level of variability within the soil microbial community was observed in the invasive range with significant effects of location, surrounding plant canopy cover, and soil chemistry on structuring these communities. Soil microbial communities in the rhizosphere of B. thunbergii were significantly different in structure between the native and introduced region, although members of the phyla Proteobacteria, Acidobacteria, and Actinobacteria were dominant in both the native and invaded regions. These data provide a holistic view of the microbes likely to be involved with plant-soil feedbacks, plant-insect interactions, and the role of human as invasive plant distributors. Future investigation needs to focus on educating horticulture industry professionals about invasive plants, obtaining direct evidence of host-microbe associations, identifying plant induced changes to the soil microbial community structure, and the functions of microbes involved with nitrogen cycling dynamics in the invaded soil.

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