Adaptive responses to water stress in phalaris arundinacea, an invasive wetland grass

Background: Phalaris arundinacea (reed canarygrass) is a very successful invasive plant in North American wetlands, significantly impacting several ecosystem proceses. Although less common in occurrence, invasions in upland sites have also been reported. To cope with diverse or variable environments, many invasive plants have high phenotypic plasticity for morphological and physiological traits that are thought to confer higher fitness. Our objectives were to characterize plasticity of response for a number of drought stress traits and compare the responses of Phalaris genotypes collected from upland and wetland sites. To address these objectives, we conducted a greenhouse study of upland- and wetland-collected Phalaris genotypes grown in wet and dry soil conditions. The number of tillers, root:shoot ratio, specific leaf area, and concentrations of several amino acids responded in the expected, adaptive direction to growth in the dry soil treatment. Characterizing the adaptive plastic responses to abiotic stresses in invasive plants can help us understand ways in which they respond to novel environments and provides a starting point for detailed mechanistic studies of how the plastic responses of specific traits may improve fitness of invasive plants across many environments.