Salinity and inundation effects on Iris pseudacorus: implications for tidal wetland invasion with sea level rise

Authors: Grewell, Brenda; GALLEGO-TEVAR, BLANCA - University Of Seville; GILLARD, MORGANE - University Of California, Davis; Futrell, Caryn; REICHOLF, REBECCA - John Carroll University; CASTILLO, JESUS - University Of Seville

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2021
Publication Date: 6/30/2021
Citation: Grewell, B.J., Gallego-Tevar, B., Gillard, M.B., Futrell, C.J., Reicholf, R., Castillo, J.M. 2021. Salinity and inundation effects on Iris pseudacorus: implications for tidal wetland invasion with sea level rise. Plant and Soil. https://doi.org/10.1007/s11104-021-04997-8.
DOI: https://doi.org/10.1007/s11104-021-04997-8

Interpretive Summary: Coastal ecosystems are threatened by biological invasions and climate change. Estuaries are characterized by a gradient of tidal conditions ranging from highest salinity and tidal inundation ranges at the coast, to freshwater tidal conditions with reduced tidal range at the inland extent of ocean influence. Biological communities in these ecosystems are adapted to local estuarine conditions. Salinity and inundation stress levels on organisms are rapidly increasing in estuaries around the world due to ongoing climate change, through alteration of precipitation amounts and patterns, and by concomitant sea level rise. Changing salinity and inundation conditions interact with exotic species, favoring or reducing biological invasions However, little is known about how exotic plant invasions will respond to these ecosystem-level changes and current risk assessments may not be adequate for effective weed management decisions. Yellow flag iris (Iris pseudacorus L.; Iridaceae) is a perennial macrophyte native to Europe, North Africa and western Asia, which is often used as an ornamental aquatic plant in garden and ponds worldwide and has escaped cultivation and invaded natural wetlands. An invasive population of yellow flag iris is established in the expansive freshwater tidal wetlands of California’s inland Sacramento-San Joaquin Delta. The assumption has been that the species is limited to freshwater conditions. However, spread into the greater San Francisco Bay-Delta Estuary (SFE) has recently occurred. This article reports the results of a greenhouse experiment to investigate the responses of yellow flag iris to increasing salinity, inundation and their interaction. Plants were propagated from seed, and the experiment focused on the pre-reproductive juvenile life stage critical to establishment, survival and spread of the invasion. We analyzed 34 plant traits categorized into four functional groups (biomass production and allocation, leaf morphology, leaf chemistry, belowground storage and gas exchange), and their responses to three salinity levels (0.5, 17 and 35 ppt), two inundation depths (-5 and -45 cm below water surface) and their combinations. Results indicate the juvenile iris plants are highly vulnerable to increasing salinity. Even a mid-range brackish salinity concentration (17 ppt) was sufficient to induce maximum negative response effects on yellow flag iris compared to freshwater conditions. While the species showed tolerance to inundation, increasing salinity limited the capacity of the exotic iris to acclimate to greater inundation. Pre-reproductive plants of yellow flag iris are vulnerable to salinity and tidal range increases that accompany climate change-induced sea level rise. Efforts to eradicate and control expansion of invasive populations in estuaries should focus on rapid response of newly colonizing populations in freshwater tidal locations, since the successful establishment and growth of juvenile I. pseudacorus is best supported in these benign environments.

Technical Abstract: Aims: We investigated the responses of invasive Iris pseudacorus to salinity, inundation and their interaction. We hypothesized that I. pseudacorus would show poor tolerance to salinity and high tolerance to inundation, yet we expected deleterious effects in response to the interaction of these stresses. Methods: We analyzed 34 plant traits categorized into four functional groups (biomass production and allocation, leaf morphology, leaf chemistry, belowground storage and gas exchange) to three salinities (0.5, 17 and 35 ppt), two permanent inundations (-5 and -45 cm deep) and their combinations. These traits were recorded in a greenhouse experiment for pre-reproductive plants of three I. pseudacorus populations invading intertidal wetlands in San Francisco Bay-Delta Estuary. Results We detected that exotic I. pseudacorus is highly vulnerable to increasing salinity during pre-reproductive life stage. Even a mid-range brackish salinity concentration (15 ppt) was sufficient to induce maximum negative response effects on I. pseudacorus compared to freshwater conditions. Increasing salinity limited the capacity of I. pseudacorus to acclimate to increasing inundation. Conclusions: Pre-reproductive plants of I. pseudacorus are vulnerable to increasing salinity and tidal range effects of sea level rise due to climate change. Efforts to eradicate and control the invasion of I. pseudacorus in estuaries should focus on rapid response of newly colonizing populations in freshwater tidal locations, since the successful establishment and growth of juvenile I. pseudacorus is best supported in these benign environments.