Salinity and tidal inundation induce physiological stress in vascular plant species and influence their distribution and productivity in estuarine wetlands. Climate change-induced sea level rise may magnify these abiotic stressors and the physiological stresses they can cause. Understanding the potential of invasive plants to respond to predicted salinity increases will elucidate their potential niche breadth. To examine potential phenotypic plasticity and functional trait responses to salinity stress in the invasive cordgrass Spartina densiflora, we collected rhizomes from four invasive populations occurring from California to Vancouver Island, British Columbia on the Pacific Coast of North America. In a glasshouse common garden experiment, we measured plant traits associated with growth and allocation, photosynthesis, leaf pigments, and leaf chemistry and calculated plasticity indices across imposed salinity treatments. Fifteen of 21 leaf chemistry, pigment, morphological and physiological traits expressed plastic responses to salinity. When averaged across all measured traits, degree of plasticity did not vary among sampled populations. However, differences in plasticity among populations in response to salinity were observed for 9 of 21 measured plant traits. Leaf chemistry and adaxial leaf rolling trait responses demonstrated the highest degree of plasticity, while growth and allocation measures were less plastic. Phenotypic plasticity of leaf functional traits to salinity indicates the potential of S. densiflora to maintain invasive growth in response to rising estuarine salinity with climate change
