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.

预计海平面上升会将咸水推入以前较新的河口区域，而较高的盐度可能会使低盐沼暴露于通常受盐度限制的无脊椎动物中。光滑的草食草互花米草（Spartina alterniflora）（Sporobolus alterniflorus）可以防御多盐水沼泽中的草食动物，但是尚不知道互花米草的防御作用是否沿着中盐到低盐度沼泽地变化。我发现互花米草来自中盐沼沼泽的植物比来自低盐沼沼泽的植物具有更好的防御能力，从而支持了最佳防御理论。较高的盐度处理降低了碳含量，C：N和新茎生物量的产生，这些特性与耐性策略相关，表明盐度可能介导了互花米草的防御反应。此外，模拟食草动物增加了互花米草的氮含量并降低了C：N 。这表明放牧可通过改善草料质量来增加互花米草对未来草食动物的易感性。模拟的草食动物也减少了地下和新茎生物量的产生，突显了一种潜在途径，其中草食动物可以间接促进沼泽地流失，如互花米草。 在未来海平面上升的情况下，生物质对于垂直积聚和沼泽稳定至关重要。