Location: Invasive Species and Pollinator Health
Project Number: 2030-22000-029-17-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 15, 2016
End Date: Sep 15, 2021
To assess ecological, ecophysiological and biochemical mechanisms influencing the ecology, growth and spread of invasive cordgrasses (Spartina spp.) and yellow flag iris (Iris pseudacorus) within the Sacramento–San Joaquin Delta - San Francisco Estuary, and other impacted estuarine watersheds with sea level rise. The specific objective is to evaluate potential ecological, ecophysiological and biochemical mechanisms underlying differential tolerances of native and exotic cordgrass congeners and exotic iris to interactive stresses imposed by predicted increases in salinity and inundation regimes in freshwater to saline tidal ecosystems. This research will contribute to an overall evaluation of the capacity of the invasive plant species, naturalized populations, and native – exotic hybrids to maintain fitness and spread in response to climate change. Improved understanding of response thresholds of both aggressive invasive and native plant species is needed for invasive species risk assessments, and development of science-based weed management and ecological restoration strategies in the context of sea level rise.
The research team will identify native and exotic study populations of cordgrasses in San Francisco Estuary, California. In a full factorial experiment, we will subject two cordgrass parental species (native S. foliosa, alien S. densiflora from South America) and a Spartina hybrid formed in San Francisco Bay to four aqueous salinity levels (0, 15, 20, 40 parts per thousand) and three simulated tidal inundation treatments for 36 replicated treatment combinations in a randomized complete block design. Adult plants of a uniform age and size range per taxa will be collected from invaded wetlands, weighed and measured. Rhizomes will be separated and propagated for experiments. Plant growth (maximum shoot height, tiller numbers) will be assessed weekly. Data will be transformed as needed, and analyzed with repeated measures mixed model with species, inundation, salinity, time and their interactions as fixed effects. Random effects will be block and species x inundation x salinity x block. Prior to harvest we will measure apical leaf elongation and salt exudation rates, leaf gas exchange, and leaf water potential of all experimental plants. At harvest, we will measure and calculate shoot and root biomass, leaf area, photosynthetic pigment concentrations, free proline accumulation, glycinebetaine concentration, Leaf Nitrogen, Potassium, and Sodium concentrations, root porosity and nonstructural carbohydrates in storage organs. The effects of salinity, inundation and their interactions on final growth, ecophysiological and biochemical responses will be evaluated with MANOVA and post hoc tests. In Spain, Cooperator will conduct a comparative study to assess the response of Spanish native S. maritima, invasive alien S. densiflora, and their two hybrid populations (from low and high marshes) to salinity in a glasshouse experiment using a randomized complete block design, and measurement and analyses of the response variables described for the first experiment. ARS scientists and Cooperator will conduct a field study in the Delta–San Francisco Estuary to measure plant traits of yellow flag iris that has recently spread to overlap in range with cordgrasses, evaluate environmental conditions correlated with the growth and spread of this associated invasive species with sea level rise, and to acquire propagules for experiments. In the native range in Spain, the Cooperator will conduct a comparative study and will collaborate on evaluation of key quantitative plant traits underlying invasion success across salinity and inundation gradients in the Delta-San Francisco Bay and conduct comparative analyses to environmental characteristics and plant traits of the species in estuarine watershed within the native range of southwest Iberian Pennisula. The research team will collaborate on experiments to develop a predictive understanding of the response of yellow flag iris to sea level rise. Experiments to determine germination thresholds will be evaluated; and a "marsh organ" or comparable approach, positioning replicate experimental plantings across a sea level elevation gradient will be used to evaluate and compare iris response to increasing salinity and tides.