Salt Tolerance Assessment of Aquatic and Wetland Plants: Increased Salinity Can Reshape Aquatic Vegetation Communities

Salinization is a great threat to wetlands and freshwater ecosystems. Increased salinity can disturb native aquatic vegetation and provide an empty niche for invasion of non-native species. To understand the fate of aquatic flora under increased salinity levels, 14 dominant wetland species with different growth forms (submersed, amphibious, floating-leaved, emergent and woody/tree) were exposed to increased salinity conditions. The objective was to assess the salt tolerance threshold for each species and model their performance in response to a salinity gradient ranging from 0.2 to 20 parts per thousand (ppt). Plant growth and survival rate were analyzed using a nonlinear regression model to project sublethal salinity concentrations that would reduce biomass and visual quality of each species by 50% (LC50). Results showed that a few non-native species (alligatorweed: Alternanthera philoxeroides (Mart.) Griseb., torpedograss: Panicum repens L., and Brazilian peppertree: Schinus terebinthifolius Raddi) survived 20 ppt salinity, whereas all other native and non-native species perished at salinity below 10 ppt. Increased salinity can suppress salt-sensitive native plants and increase the opportunity of invasion for salt-tolerant non-native species. This suggests that alligatorweed, torpedograss and Brazilian peppertree pose a more significant threat to the ecosystem if salinity levels continue to increase in freshwater ecosystems and exacerbate the encroachment of non-native species into native plant communities.