Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Advisor

Dyck, Larry

Committee Member

Riley , Melissa B

Committee Member

Wells , Christina

Committee Member

McInnis , Tom

Abstract

Reservoirs in upstate South Carolina are subject to erosion and vegetation has been placed to help stabilize banks, but soils are nutrient-poor and have high bulk densities. Panicum virgatum L. (switchgrass) has been planted in several sites, and it is hypothesized that over time, changes in microbial activity and soil quality will occur in response to the planting. As vegetated sites aged, acid phosphomonoesterase, nitrate reductase, and dehydrogenase activity increased. Low values of nitrogen fixation and substrate-induced respiration were measured at all sites with no statistical differences between sites. Fatty acids indicative of Gram negative bacteria were found in vegetated sites and the diversity of fatty acids increased in vegetated sites indicating more diverse microbial communities.
Switchgrass plants may experience periods of flooding resulting in ethylene production. Switchgrass plants were placed in a modified Hoagland's solution and treated with an ethylene producer and ethylene inhibitor to determine morphological responses. Ethylene treatment resulted in increases in the number of adventitious roots. No effects were observed on aerenchyma development, shoot elongation, root length, average root diameter, root system volume, or root surface area. Switchgrass therefore does not appear to be sensitive to ethylene which may be produced in response to flooding resulting in no effect on switchgrass growth.
Serratia ficaria, an ACC deaminase bacterium, was isolated from lakeshore soils and then added to switchgrass seeds/young plants to determine its effect as a plant growth-promoting bacterium (PGPB) under three different water regimes. Treatments inoculated with bacteria had increased root to shoot ratios in unflooded and completely submerged water regimes, but the opposite was true for crown-flooded treatments. Shoot growth was fastest in inoculated treatments, except for completely submerged treatments, where values were not statistically different between inoculated and uninoculated groups. The bacterium was beneficial when there is no water stress, but became detrimental when water levels rose until submergence.
Overall switchgrass appears to increase microbial activity and diversity over time, has limited response to ethylene due to flooding and is able to grow in soils with minimal nutrients making it a good plant for use in lakeshore stabilization along Lake Hartwell.

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Plant Biology Commons

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