Morphological and reproductive responses of coastal pioneer sedge vegetation to inundation intensity

Coastal plants have unique adaptability to cope with strong hydrological stresses in tidal wetlands. A fundamental understanding of the establishment and maintenance of coastal plants is needed for conservation and restoration. In the Yangtze Estuary, the plasticity of the morphological and reproductive traits of a pioneer Scirpus species (sedge), in terms of phenotypic growth, biomass allocation, and sexual and asexual reproductive traits, was investigated with increasing flooding intensity (elevation gradient) in a tidal flat. The varying response extents (thresholds) of plant zonation and morphological and reproductive traits to multiscale environmental heterogeneity were also assessed. Our results showed that plant colonization and performance at coastal frontiers are sensitive to the microtopography of elevation and reflect the ecological adaptability at both the landscape and individual scales. Sedge species typically exhibit morphological and reproductive flexibility across the inundation intensity. The plants allocated more biomass to belowground tissues in response to decreasing elevation. The elevation thresholds for the yield of reproductive organs were higher (2.38–2.50 m based on the local Wusong datum) than those for morphology (2.05–2.14 m). The thresholds for the yield of asexual reproductive organs shifted to a lower elevation by approximately 0.15 m relative to that of the sexual reproductive organs. The increasing corm: spike ratios of plants with longer inundation durations also indicated this reproductive plasticity. This study revealed that the combination of morphological and reproductive responses of pioneer sedges contributed to survival and colonization at the foremost coastal flat. Our results are useful for developing restoration strategies for the native Scirpus species on China's coast.