Is there evidence of local adaptation of Phragmites australis to water level gradients and fluctuation frequencies?

Greater differences in hydrologic conditions are expected between coastal and inland wetlands with global climate change. Local adaptation has been considered as a significant driver of intraspecific differentiation in heterogeneous habitats. The common reed Phragmites australis is a cosmopolitan wetland species with high genetic variability and adaptability. In our study, reeds collected from coastal and inland wetlands were subjected to three stable water level gradients and two fluctuation frequencies in a common garden experiment. We measured their aboveground and belowground biomass, height, density, stem diameter, leaf water potential, specific leaf area, and photosynthetic parameters. Our results showed that P. australis exhibited high tolerance to stable and fluctuating water levels up to 30 cm depth. Increased shoot elongation rate and water-use efficiency promoted the establishment of P. australis in flooding habitats. The common reeds in the high-frequency water level fluctuation had a shorter shoot height and a lower shoot density than those in the low-frequency one. The coastal populations performed better under high (30 cm) and low (0 cm) water levels than the inland populations, which preferred shallow water (15 cm). The adaptation strategies of coastal and inland reeds to fluctuation frequencies were no different. We concluded that local adaptation might occur in P. australis populations due to different water levels rather than fluctuation frequency in coastal and inland wetlands. Our findings could provide a theoretical basis on the effects of flooding on intraspecific variation of wetland plants in future environmental change scene.