Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora

Authors: Grewell, Brenda; Skaer Thomason, Meghan; CASTILLO, JESUS - University Of Sevilla; DRENOVSKY, REBECCA - John Carroll University

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2015
Publication Date: 7/17/2016
Citation: Grewell, B.J., Skaer Thomason, M.J., Castillo, J.M., Drenovsky, R.E. 2016. Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora. Biological Invasions. 18:2175-2187.

Interpretive Summary: Estuaries are areas where rivers meet the sea and a blending of saline tidewater mixes with fresh river flow. These unique brackish ecosystems are among the most productive in the world, supporting unique fish, wildlife and plant species. Large urban areas often border estuaries and people benefit from food, recreation, jobs, shipping commerce and flood protection supported by estuarine ecosystems. Estuaries are also highly invaded systems, and nuisance aquatic species can disrupt coastal biological resources and entire food webs. Cordgrasses are highly aggressive marsh grass species that alter both the physical structure and biological communities of estuaries. Pacific coast estuaries of the western United States are compromised by invasive cordgrasses from Europe and Atlantic marshes of the Americas. Our estuaries and coastal communities are facing multiple impacts from rising sea level and atmospheric temperature, and these factors in turn will impose increased physiological stress on plant species. Little is known about how invasive species will respond to these global environmental changes. Understanding the basic biochemical and physiological responses of invasive cordgrasses to predicted salinity is needed to improve risk assessments and management to curtail the spread and impact of invasive aquatic weeds. To examine functional trait responses to salinity stress and the phenotypic plasticity of key plant traits invasive austral cordgrass Spartina densiflora from southern South America, we collected rhizomes from four invasive populations occurring across 12 degrees of latitude 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. Leaf chemistry, pigments, morphology and physiology all expressed plastic responses to salinity, and significant population differentiation was also observed for several measured plant traits. Growth and allocation measures were less plastic, with the exception of total leaf area. The ability of austral cordgrass to adjust to through phenotypic plasticity of leaf functional traits may support invasive plant growth in response to rising estuarine salinity.

Technical Abstract: 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 is magnifying these abiotic stressors and the physiological stresses they 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. Leaf chemistry, pigments, morphology and physiology all expressed plastic responses to salinity, and significant population differentiation was also observed for several measured plant traits. Growth and allocation measures were less plastic, with the exception of total leaf area. Phenotypic plasticity of leaf functional traits may support invasive plant growth in response to rising estuarine salinity.