Climate change effects shift distributions of grass species that stabilize coastal sediments and offer protection to inland communities. Coastal species are sensitive to climate change as they are influenced by both atmospheric and oceanic drivers (i.e. changes in temperature, precipitation, and sea level rise). To understand the tolerance of coastal grasses to climate change stressors, our objective was to compare the physiological responses of two dominant grassland species (Spartina patens and Fimbristylis castanea) under saline flooding conditions. Field collected plants were subjected to varying levels of salinity (0, 5, 10, 15, and 20 g L-1) for six weeks. Measurements were taken for functional traits and physiological responses, which included stomatal conductance (gs), electron transport rate (ETR), water potential (ψ), specific leaf area (SLA), tissue chlorides, and biomass. As S. patens is a dominant species across multiple habitats in coastal ecosystems compared to F. castanea, we hypothesized that S. patens would exhibit physiological tolerance to a wider range of salinity concentrations.
Results/Conclusions
Both species exhibited physiological responses to increased salinity. Although water relations (gs and ψ) exhibited a significant species x treatment interaction (p < 0.0001), reduced values at higher salinity concentrations did not indicate severe water stress. ETR was reduced in both species at higher salinity concentrations with the lowest values exhibited by F. castanea at 20 g L-1. SLA was significantly higher in S. patens (p < 0.0001), but there was not a significant treatment effect (p = .05). Tissue chlorides were significantly higher due to salinity treatment in F. castanea (p < 0.0001), with tissue chloride levels doubling S. patens at 20 g L-1. Salt excretion was visible in S. patens. Even at the highest levels of salinity, both species maintained photosynthetic ability, with F. castanea exhibiting higher stress at 20 g L-1 and subsequent reductions in biomass. Overall, Spartina patens was more tolerant to the highest levels of salinity than F. spadicea. This outcome reflects the varied distribution of S. patens. As sea-level rises in coastal communities, our results demonstrate that S. patens is highly responsive to effects associated with climate change and will continue to be an important species in shaping coastal communities.