Date on Master's Thesis/Doctoral Dissertation

8-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Degree Program

Biology, PhD

Committee Chair

Emery, Sarah

Committee Member

Christian, Natalie

Committee Member

Kolmann, Matt

Committee Member

Mehring, Andrew

Committee Member

Day, Christopher

Author's Keywords

coastal; functional traits; global change; nitrogen; endophyte; plant traits

Abstract

We live in a time of rapid global change with substantial consequences for planet-wide functioning. Local ecosystems reflect this change, yet we struggle to predict their responses. Coastal ecosystems, like dune and interdunal wetlands, have declined rapidly and predicting their responses to global change is essential for future management. Functional traits may be particularly informative as they drive species and ecosystem responses and can provide generalizable findings. This dissertation investigates how global change, especially anthropogenic nitrogen (N) enrichment, interacts with abiotic and biotic factors to affect coastal sand dune and interdunal wetland plant functional traits. First, I used a long-term experiment to investigate the effects of N enrichment and a fungal endophyte on functional traits and productivity of a dominant sand dune species. I found that both N enrichment and the fungal endophyte had individual effects on plant traits but interactively affected productivity. Next, I investigated how these factors affected the functional traits of colonizing species. Even realistic levels of N enrichment promoted the growth of larger, faster growing plants while high levels of N enrichment suppressed functional trait diversity, with implications for ecosystem stability and resilience. The fungal endophyte suppressed N enrichment effects on a community-level root trait, which may indicate that it has indirect effects on belowground functioning. Lastly, I examined the responses of two dominant dune and interdunal wetland plants to key global change drivers. Following a field survey, wetland plant traits varied substantially across a broad gradient, while total N was a significant, though weak, environmental predictor of trait variation in both species. N enrichment increased aboveground growth in both species in a growth chamber experiment, while burial enhanced and suppressed these effects in the dune and wetland species, respectively. While these interactive effects may promote dune stabilization and recovery following storms, they may increase the vulnerability of interdunal wetlands to overstabilization and changing hydrology. I found that interactive effects of abiotic and biotic factors are difficult to predict, yet evaluating responses using plant functional traits could provide generalizable insights into ecosystem responses to global change.

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