Ridge crest versus swale: contrasting plant-water relations and performance indexes in two understory plant species in a coastal maritime forest

Coastal-ridge plains are progradational landforms composed of elevated ridges and low-lying swales. The transitions between ridges and swales are steep, promoting dynamic shifts between xeric and mesic systems. Two understory plants that co-occur in ridge plains of North American mid-Atlantic maritime forests are Sabal minor and Ilex vomitoria. As coastal-ridge plains foster varying amounts of surface and sub-surface water driven largely by topography, the purpose of this study was to evaluate plant-water relations and chlorophyll a fluorescence in these two species. Ridge plants had lower leaf-and xylem-water potentials, lower osmotic potential (I. vomitoria), and lower symplastic water content (S. minor). Although there were no differences in potential- and effective-quantum yields, there were decreases in fluorescence performance index for ridge I. vomitoria and swale S. minor. While the data support potential water-stress conditions in ridge plants of both species, the data also suggest that I. vomitoria and S. minor use different physiological processes to tolerate hydrologically dynamic ridge-swale maritime forests.