Semester of Graduation

Spring 2025

Degree

Master of Science (MS)

Department

Department of Oceanography & Coastal Sciences

Document Type

Thesis

Abstract

Phragmites australis is a widespread wetland plant species with numerous haplotypes, several of which are highly invasive. In low-lying coastal marshes of Louisiana, the Delta-type (haplotype M1) dominates across a wide range of salinity and flooding environments. This suggests that Phragmites may be highly adaptable to diverse environmental conditions and that there may be a genetic component, as seen in other coastal wetland plant species. While non-native Phragmites haplotypes are targeted for control and removal in many areas, they are considered beneficial for marsh stabilization and contributing to elevation gain in coastal Louisiana, where several areas experience rapid land loss. To investigate intraspecific variation in Phragmites tolerance to flood and salinity stress, I examined exposure of Delta-type Phragmites to salinity and water levels (2019 – 2024) across the Louisiana coast using a large network of monitoring sites. Five populations that differed in flooding and salinity conditions were selected and a field survey of the source populations and a controlled greenhouse experiment were conducted to test intraspecific variation in salinity and flooding tolerance. Replicate plugs from the five Phragmites populations were subjected to flooding (50 and 100% time flooded above the surface) and salinity treatments (0, 10, 25, 40 ppt) for 75 days. In addition to physiological and morphological measurements, I collected leaves for metabolomic and transcriptomic analysis to determine what mechanisms the plants are using in response to these stressors. By the end of the experiment, photosynthetic rates differed among treatments. Thus, populations responded similarly to treatment conditions with respect to carbon fixation. Rockefeller, which had the greatest pre-exposure to salinity and flooding in its field environment had the greatest number of live stems and aboveground biomass production while the population pre-exposed to low salinity MRD Pass-a-Loutre the lowest. Understanding how to control and promote Phragmites relies on knowledge of its tolerance to environmental conditions and the potential use of populations with different adaptations to abiotic stress. Results from the present study suggest that populations of Delta-type Phragmites from more flood and salinity stress sites possess genetic adaptations that allow them to thrive under severe flood and salinity stress.

Date

4-3-2025

Committee Chair

Tracy Quirk

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