Defense Date
2026
Document Type
Thesis
Degree Name
Master of Science
Department
Biology
First Advisor
Dr. Donald Young
Abstract
Shrub expansion across Atlantic and Gulf coasts has been observed for decades, mirroring global trends of woody encroachment. Morella cerifera, an evergreen nitrogen-fixing shrub, is the most extensive woody species spreading across the mid-Atlantic coast. Yet low salt tolerance combined with reliance on rainwater-charged freshwater lenses leave the species vulnerable to saltwater intrusion and drought on barrier islands, both of which are expected to become more extreme with climate variability. Although much is known about mechanisms leading to M. cerifera expansion, knowledge gaps remain regarding effects of these climate-linked stressors on coastal shrub hydraulic traits–like sap flux–which may lend insight into how M. cerifera communities will respond to ongoing stress. Given the coupling of woody cover and barrier island sediment dynamics, quantifying physiological tolerance in M. cerifera is important in projecting barrier island resilience over time. My study assessed physiological responses in M. cerifera to short-term salt and drought stress in glasshouse conditions. 1 m tall shrubs were divided among three treatments–control, drought exposure, and salt exposure–and administered three stress trials over two months (Oct-Nov 2025) (n = 4). Treatments occurred approximately once every two weeks when average daytime cloud cover did not exceed 50%. Plants were watered every two days under control conditions. Drought exposure consisted of withholding a single scheduled watering, and salt exposure consisted of a single watering with saline water (5, 10, and 15 ppt for trials 1-3). Stress exposures were followed by a return to the control watering regime on day 3 to assess recovery. Midday stomatal conductance, leaf water potential, and normalized sap flux were quantified for 5 days beginning immediately before treatment. Midday stomatal conductance, leaf water potential, and normalized sap flux were
significantly affected by drought, typically 1-2 days after exposure, before recovering to match or exceed measurements from control shrubs. Conversely, significant effects of salt were observed in sap flux readings after exposure to 15 ppt saline water, occurring four days after exposure. Morella cerifera is able to withstand short term (i.e., 3 days) salinity events up to 15 ppt without long-term physiological consequences as may be expected with increased storms and sea level rise. Future studies will include analogous field measurements to determine if experimental physiological responses are observed in the less controlled barrier island environment.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-8-2026