Salinity and Simulated Herbivory Influence Spartina alterniflora Traits and Defense Strategy
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SHORT COMMUNICATION
Salinity and Simulated Herbivory Influence Spartina alterniflora Traits and Defense Strategy Serina Sebilian Wittyngham 1 Received: 18 June 2020 / Revised: 10 September 2020 / Accepted: 25 September 2020 # Coastal and Estuarine Research Federation 2020
Abstract Sea level rise is expected to push saline waters into previously fresher regions of estuaries, and higher salinities may expose oligohaline marshes to invertebrate herbivores typically constrained by salinity. The smooth cordgrass, Spartina alterniflora (syn. Sporobolus alterniflorus), can defend itself against herbivores in polyhaline marshes, however it is not known if S. alterniflora’s defense varies along the mesohaline to oligohaline marsh gradient in estuaries. I found that S. alterniflora from a mesohaline marsh is better defended than plants from an oligohaline marsh, supporting the optimal defense theory. Higher salinity treatments lowered carbon content, C:N, and new stem biomass production, traits associated with a tolerance strategy, suggesting that salinity may mediate the defense response of S. alterniflora. Further, simulated herbivory increased the nitrogen content and decreased C:N of S. alterniflora. This indicates that grazing may increase S. alterniflora susceptibility to future herbivory via improved forage quality. Simulated herbivory also decreased both belowground and new stem biomass production, highlighting a potential pathway in which herbivory can indirectly facilitate marsh loss, as S. alterniflora biomass is critical for vertical accretion and marsh stability under future sea level rise scenarios. Keywords Functional traits . Plant defense strategy . Resistance . Salt marsh . Tolerance
Introduction Tidal marshes are responsible for ecosystem services that contribute to human well-being including carbon sequestration, erosion control, and nutrient cycling (de Groot et al. 2012; Costanza et al. 2014). Tidal marshes occur along natural salinity gradients within estuaries and are typically categorized by their salinity regime (e.g., oligohaline 0 to 5 ppt, mesohaline 5 to 18 ppt, and polyhaline 18 to 30 ppt) (Odum 1988; Montagna et al. 2013). In the Chesapeake Bay region, accelerated sea level rise is a threat to tidal marshes (Najjar et al. 2010). Average sea level rise in this region is ~ 3.80 mm
Communicated by R. Scott Warren Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12237-020-00841-x) contains supplementary material, which is available to authorized users. * Serina Sebilian Wittyngham [email protected] 1
Virginia Institute of Marine Science, William & Mary, 1370 Greate Road, Gloucester Point, VA 23062, USA
yr−1, which is 3–4 times higher than the global mean of ~ 0.98 mm yr−1 (Sallenger Jr. et al. 2012; Boon and Mitchell 2015). A marsh’s ability to keep pace with sea level rise depends on sediment size and supply (Kirwan et al. 2010), and vegetation stem density and biomass production, both aboveand belowground (Leonard and Luther 1995; Elsey-Qui
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