Date of Award

Spring 2009

Document Type

Restricted Thesis

Terms of Use

© 2009 Marissa Lee. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

José-Luis Machado

Abstract

Japanese Stiltgrass (Microstegium vimineum) is the most invasive grass in the southeastern US. Shade tolerance and rapid nutrient acquisition are believed to be central to its invasibility. However, the underlying mechanisms that facilitate M. vimineum nutrient acquisition are unclear. Two experiments were conducted in growth chambers to examine whether M. vimineum form symbiotic associations with arbuscular mycorrhizal fungi (AMF) and thus confer a competitive advantage for nutrients. M. vimineum was grown (1) in pre-invaded field soil (Orig) and sterilized pre-invaded field soil (Stm) to determine the plant-soil feedback and (2) in the sterilized soil with a mixture of AMF inocula (Stm+AM) to determine the AM effect. Two additional treatments of N addition (Orig+N) and AMF inoculum addition (Orig+AM) to pre-invaded field soils were used to examine nutrient release effects from soil sterilization and baseline mycorrhizal activity in the field soil, respectively. M. vimineum was found to be highly mycorrhizal with infection rates of 38-71%. Compared to growth in the field soil (control), M. vimineum biomass increased 4.4-fold in the sterilized soil and 5.4-fold in sterilized soil with mycorrhizae 64 days after germination from seed. Morphological differences were also observed. With added AMF inoculum, the presence of branches and aerial roots increased 1.5 and 4.7-fold for plants grown in the field soil and 1.4 and 6.7-fold for plants grown in the sterilized soil. Mycorrhizal stimulation of branch and aerial root formation may serve as another mechanism by which M. vimineum can quickly take over new territory. Future studies on invasive plant-microbial interactions, such as this one, will continue to build our theoretical understanding of plant invasions and inform management strategies.

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