Portland State University. Department of Environmental Sciences and Resources
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources
Environmental Sciences and Resources
Plant physiology -- Oregon, Plant physiology -- California, Fresh water -- Oregon, Fresh water -- California
1 online resource (2, viii, 153 pages)
Many rooted macrophytes form a dense canopy on the water surface that is detrimental to aquatic organisms, water quality, navigation, and recreation. Control of invasive macrophytes may be improved when management activities are linked to the plant's biology. The purpose of this research was to evaluate seasonal changes in the morphology, growth rates, allocation patterns and photosynthetic responses of a clonal submersed macrophyte. Egeria densa Planch. (Hydrocharitaceae) is highly invasive in the USA where it forms dense surface canopies in freshwater ecosystems. Using E. densa the following hypotheses were evaluated: (1) flowering stems have reduced capacity for vegetative growth as flowers preclude the formation of vegetative buds, (2) there are seasonal low points in total nonstructural carbohydrates (TNC) and nitrogen (N) that could be identified to improve control, (3) establishment success of stem fragments increases with stem length, and (4) photosynthetic rates are higher during the summer. These hypotheses were evaluated in situ and under greenhouse conditions using E. densa from coastal populations in Oregon and California. Results indicate that flower production does not preclude bud or root formation, resulting in continued growth of ramets during flowering. Longer stem fragments established more successfully than shorter stem fragments. Floated stems rapidly grew adventitious roots and showed no signs of decay despite floating in tap water for 13 weeks. Seasonal low points in TNC and N concentration were identified; however, they were inconsistent between years and among plant parts, suggesting low points may not reliably predict vulnerable periods in the plant's life cycle. Higher photosynthetic rates were measured during the summer with a stronger correlation with degree day than temperature, indicating seasonal light history is important in photosynthetic responses. Growth rates were higher in California, possibly due to increased light availability or higher water temperature. Overall, E. densa from both populations grew within its optimal temperature range (14° to 25 °C) and as an evergreen. These data may be used to model the plant's response to changes in the environment, predict its ability to spread to nearby waterways, and improve management by linking control activities to the biology of the plant.
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Pennington, Toni Garrett, "Seasonal Changes in Allocation, Growth, and Photosynthetic Responses of the Submersed Macrophyte Egeria densa Planch. (Hydrocharitaceae) from Oregon and California" (2007). Dissertations and Theses. Paper 5981.