Responses of Four Peatland Emergent Macrophytes to Salinity and Short Salinity Pulses

Sea-level rise intensifies saltwater influx into coastal wetlands causing osmotic stress and probably changing vegetation composition. To determine especially the impact of salinity pulses that occur during flooding events, Typha latifolia, Carex acutiformis, Schoenoplectus tabernaemontani and Phragmites australis were exposed to different salinity regimes consisting of control (permanently freshwater and permanently brackish water) and alternating freshwater and brackish water with different exposure durations (2 days brackish - 2 days fresh; 4 days brackish - 4 days fresh; 2 days brackish - 4 days fresh). Plant height, leaf area, chlorophyll fluorescence, root:shoot ratio and photosynthetic pigments were measured. Salinity suppressed the growth of T. latifolia resulting in shorter height, smaller mean leaf area and higher root:shoot ratio. Carex acutiformis had smaller mean leaf area and higher root:shoot ratio. Photosynthetic pigment and chlorophyll fluorescence of both species were not affected. Shorter but frequent salinity pulses (alternate 2 days brackish - 2 days freshwater, and 2 days brackish - 4 days freshwater) decreased the leaf area of T. latifolia while C. acutiformis was not affected. Salinity and salinity pulses did not affect the height and root:shoot ratio of P. australis and S. tabernaemontani. Phragmites australis showed signs of successful acclimation through decreased chlorophyll a:carotenoid ratio and high fluorescence Delta yield at low and high irradiance. Our results imply that with increasing seawater influx into coastal peatlands, T. latifolia and C. acutiformis may experience growth retardation or may even be replaced by S. tabernaemontani or P. australis since they are more resilient against salinity and frequent salinity pulses.