While saltmarsh communities are endangered in many parts of the world due to anthropogenic impact, the risk of invasion by exotic plants is considered to be low because of their saline conditions. However, in urban areas, saltmarshes receive high nutrient freshwater input through stormwater discharge. We tested if invasion of saltmarsh by exotic plant species was facilitated by increased nutrients and reduced salinity associated with urban stormwater input. In a manipulative glasshouse experiment, we grew saltmarsh communities under four treatments: high salinity–low nutrients (control), high salinity–high nutrients, low salinity–low nutrients and low salinity–high nutrients. We then invaded the saltmarsh communities with four common invasive exotic plants. Their survival rates were monitored weekly for seven weeks before final harvesting. All exotic species showed significantly higher survival in the ‘low salinity’ treatment compared to the ‘high salinity’ treatment. There was variability among species, with three of four having low survival rates (0–3%) under ‘high salinity’ conditions, while survival of Protasparagus aethiopicus was reduced to only 53–59%. Our findings suggest that under natural conditions of saltmarshes, the establishment of exotic plant seedlings is restricted. Additional freshwater increased the survival of invading exotic species significantly, whereas adding nutrients increased biomass production but not necessarily survival of exotics. However, the results can be highly species dependant as shown by the unexpected salinity tolerance of P. aethiopicus. Reduction in salinity of saltmarsh due to stormwater input facilitates invasion by exotic plant species that would otherwise be unable to tolerate the highly saline environment.

中文翻译：

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淡水输入推动了盐沼社区外来植物的入侵成功

虽然由于人为影响，盐沼群落在世界许多地方都处于濒危状态，但由于其盐碱地条件，外来植物入侵的风险被认为很低。然而，在城市地区，盐沼通过雨水排放获得高营养的淡水输入。我们测试了与城市雨水输入相关的养分增加和盐度降低是否会促进外来植物物种对盐沼的入侵。在一个操作温室实验中，我们在四种处理下种植盐沼群落：高盐度-低营养（对照）、高盐度-高营养、低盐度-低营养和低盐度-高营养。然后，我们用四种常见的外来入侵植物入侵了盐沼社区。在最终收获前的七周内每周监测它们的存活率。与“高盐度”处理相比，所有外来物种在“低盐度”处理中的存活率显着提高。物种之间存在差异，在“高盐度”条件下，四个中的三个具有低存活率（0-3%），而Protasparagus aethiopicus减少到只有 53-59%。我们的研究结果表明，在盐沼的自然条件下，外来植物幼苗的建立受到限制。额外的淡水显着增加了入侵外来物种的存活率，而添加养分增加了生物量生产，但不一定增加了外来物种的存活率。然而，正如P. aethiopicus出乎意料的盐度耐受性所示，结果可能高度依赖于物种。由于雨水输入导致盐沼盐度的降低促进了外来植物物种的入侵，否则这些物种将无法忍受高盐度环境。