Changes in water availability in coastal wetlands resulting from increased storm surge intensity and sea level rise may alter local plant community composition leading to decreased species diversity and shifts in community composition, especially at the upper end of coastal wetland gradients where species are less likely to be salt tolerant. Understanding the physiological response of species to salt water flooding will contribute to a mechanistic understanding of potential community changes as a result of storm surges and sea level rise. We hypothesized that individuals subjected to storm surges would experience decreased xylem water potential and decreased leaf chlorophyll contents as a result of increased soil salinity and aboveground exposure to salt water, and that these responses would be most pronounced in plant communities located in upper elevations of wetlands. We compared mid-day and pre-dawn water potentials and leaf chlorophyll content in experimentally surged plots before surging and 1 day after surging, and in control and surged plots 42 days after surging in a freshwater marsh and an upstream pine savannah on Eglin Air Force Base on the Florida coast. The most common species sampled in the pine savannah plots were Cyrilla racemiflora, Quercus minima, and Ilex glabra; in the marsh plots Eriocaulon decangulare, Cladium mariscus, Hypericum fasciculatum , and Phelypteris palustris were the most common
Results/Conclusions
Pre-dawn water potentials 1 day post-surge were lower for all species sampled in the pine savannah plots, although differences were only significantly lower for C. racemiflora and I. glabra, and for P. palustris in the freshwater marsh plots; after 42 days, there were no differences in pre-dawn water potentials between surged and control plots regardless of location. Leaf chlorophyll content was significantly lower for most species in the pine savannah plots 1 day post surge, but higher 42 days post-surge. In the marsh plots, chlorophyll content decreased in P. palustris 1 day after the surge, but increased after 42 days post-surge. Lower post-surge pre-dawn water potentials in the pine savannah indicate decreased soil water availability, which did not occur in the marsh. Similar mid-day water potentials suggest that lower water availability and disruption of the photosynthetic apparatus by salt water in surged plots may force earlier stomatal closure to avoid more negative water potentials at mid-day. Although these effects were ephemeral, longer term exposure to saline conditions and prolonged surges may result in more permanent effects for some species.
