Tidal marshes have a remarkable ability to sustain themselves and maintain the many economic services they provide, including shoreline stabilization and flood protection. However, current trends show thousands of hectares of low-lying coastal wetlands are lost to open water each year, with impacts on fisheries, wildlife habitat, water quality, and adjacent human infrastructure. The ability of a coastal marsh to self-sustain depends largely on the highly productive vegetation generating new organic matter. The objective of this project is to learn how tidal marshes respond to changing coastal conditions. This project examines the influence of atmospheric carbon dioxide, nutrients, plant traits, and water level on the structure and persistence of tidal marsh vegetation. It aims to take advantage of an unparalleled forty-year record of plant, microbe, and soil responses to environmental fluctuations and fertilization to identify the most important factors for marsh survival and coastline integrity. This project will extend a globally unique, AI-ready dataset of plant growth, leaf chemistry, soil chemistry and soil elevation change. It also extends an equally unique archive of genetic samples of plants that enable assessment of the most valuable genotypes for sustaining marshes under variable conditions. These samples and data are a resource for developing biotechnological solutions to marsh restoration and coastal protection. This LTREB project includes three complementary, long-term field experiments that manipulate atmospheric carbon dioxide and nitrogen enrichment in different plant communities, leveraging the inter-annual variability in other critical factors such as water level, salinity, and precipitation. The team will test the hypothesis that changes in water level are the ultimate driver of resilience in coastal wetlands and will cause the two plant species with the highest flood tolerance (native sedge and invasive Phragmites australis) to replace the sp