Master's Theses



Degree Name

Master of Science (MS)


Invasion by nonnative plants is particularly prevalent in wetlands. While the ecological patterns in wetland plants are well known, it is less well known how flooding-related soil conditions influence the physiological success of introduced species in wetlands. In chapter 1, effects of flooding were measured in invasive common reed (Phragmites australis), reed canary grass (Phalaris arundinacea), Johnson grass (Sorghum halepense), and native prairie cordgrass (Spartina pectinata). The four species were kept at four levels of flooding (deep flooding, medium flooding, low flooding, and dry conditions), and their responses were measured after 7 and 28 days of treatment using by a Li-Cor LI-6400 photosynthesis and fluorescence system. Measurements included light harvesting abilities, CO2 fixation rates, leaf carbon isotope ratios, and root anaerobic enzyme activities. CO2 fixation and light harvesting abilities in Phragmites were maximized at deep flooding conditions whereas they were maximized in Phalaris at medium flooding conditions. Light harvesting abilities in Sorghum were maximized at deep flooding conditions after 7 days. However, at 28 days most of the Sorghum had died. Native Spartina had the lowest light harvesting and CO2 fixation abilities after 7 days of flooding. After 28 days of flooding, light harvesting abilities of Spartina were maximized at deep flooding levels, but the rates were lower than Phragmites. In chapter 2, flooding-sensitive Sorghum halepense and flooding-tolerant Phragmites australis (n=5) were flooded to 8 cm depth or kept dry for 7 days. Transpiration, stomatal conductance, boundary layer conductance, and vapor conductance were measured for each. Transpiration was significantly higher in drained treatments compared to flooded treatments for Sorghum. However, transpiration was significantly higher in flooded treatments compared to drained treatments for Phragmites. Thus, there was a significant species x treatment interaction in transpiration. A similar interaction was detected in both stomatal and vapor conductances. Phragmites had increased stomatal conductance when flooded, which indicated a high physiological tolerance to waterlogged soils. This allowed Phragmites to photosynthesize under waterlogged conditions and to be successful as wetland invaders. Further information on the conditions that maximize stomatal opening for Phragmites can help management efforts. By contrast, stomatal conductance in Sorghum was decreased under flooding, indicating a greater sensitivity to flooding. The sampled population of Sorghum is therefore not a threat to invade chronically flooded soils based on these results. Additional work will be needed to test the ability of Sorghum to acclimate to wet environments. Increased photosynthesis rates under flooded conditions, especially in short-term flooding, might help invasive grasses to invade wetland settings.


Dr. Brian Maricle

Date of Award

Spring 2010

Document Type



© 2010 Elizabeth Waring


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