Multiple Potential Stressors and Dieback of Phragmites australis in the Mississippi River Delta, USA: Implications for R
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GENERAL WETLAND SCIENCE
Multiple Potential Stressors and Dieback of Phragmites australis in the Mississippi River Delta, USA: Implications for Restoration James T. Cronin 1
&
Joseph Johnston 1 & Rodrigo Diaz 2
Received: 29 April 2020 / Accepted: 10 August 2020 # Society of Wetland Scientists 2020
Abstract In 2016, widespread dieback of Phragmites australis was reported in the Mississippi River Delta (MRD), Louisiana. We conducted two common-garden experiments to investigate several potentially important factors associated with this dieback: scale insects, water depth, fertilization and P. australis genetics (three lineages: Gulf, Delta and invasive EU). Predictions tested were scale abundance is lower in high water, at low fertilization, and for EU; plant biomass is negatively impacted by scales, high water and high fertilization; and EU suffers the least damage from the three potential stressors. Scale abundance was 41% lower in high water and decreased 2.7 fold as fertilization increased. Also, EU had 1.5–2.6 times fewer scales than Gulf, but had similar scale abundance to Delta. Impacts of scales, water depth and fertilizer on plant biomass depended strongly on lineage. Scales reduced biomass of Delta, EU and Gulf by 38%, 32% and 10%, respectively. In comparison, biomass was 30% higher for EU, 46% lower for Gulf and unchanged for Delta in high versus low water. Finally, at high fertilization levels, Gulf produced 57% more biomass than EU. Owing to its greater tolerance to scales and high water, EU may be most suitable for use in restoration of the MRD. Keywords Dieback . Herbivory . Fertilization . Nipponaclerda biwakoensis . Scale insects, water depth
Introduction The fragility of coastal wetlands and marsh ecosystems is clearly evident from the relatively common occurrence of widespread dieback of dominant or foundation plant species. Dieback is typically characterized by stunted growth of stems, premature senescence of leaf tissue, the presence of dead meristematic tissue, and increased patchiness in the distribution of plants, usually over broad spatial scales (Mendelssohn and McKee 1988; Armstrong et al. 1996b; Clevering 1997; van der Putten 1997; Alber et al. 2008; Gigante et al. 2011). Dieback has occurred with salt-marsh cordgrass (Spartina Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-020-01356-8) contains supplementary material, which is available to authorized users. * James T. Cronin [email protected] 1
Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
2
Department of Entomology, Louisiana State University, Baton Rouge, LA 70803, USA
alterniflora Loisel = Sporobolus alterniflora; Poaceae) in the USA (Mendelssohn and McKee 1988; McKee et al. 2004; Alber et al. 2008; Elmer et al. 2013), common reed (Phragmites australis (Cav) Trin. ex Steud.; Poaceae) throughout Europe (van der Putten 1997; Brix 1999) and in China (Li et al. 2013), seepweed (Suaeda salsa L.) in China (He et al. 2017), and mangrove for
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