We studied a mesotrophic and a hypertrophic Mediterranean coastal lagoon, both of which had been simultaneously subjected to a nutrient input reduction for 9 yr. We compared these 2 lagoons to an oligotrophic coastal lagoon. Using bioassays comprising 24 h incubations with added phosphorus and/or ammonium, we investigated the response of the phytoplankton communities to nutrient enrichment during summer in terms of biomass, size class structure, abundance and growth. For nitrogen and phosphorus, we identified which nutrient limited phytoplankton growth, and what strategies of nutrient exploitation the communities adopted to cope with these limitations. Ultraphytoplankton dominated the 3 communities, but it differed in composition among the lagoons. Green algae dominated in the hypertrophic lagoon, whereas the mesotrophic lagoon presented a higher diversity of phytoplankton groups. Picocyanobacteria and small diatoms were the most abundant groups in the oligotrophic lagoon, although they accounted for less biomass than green algae. The communities of the mesotrophic and the hypertrophic lagoons strongly responded to the nutrient pulse, showing that the re-oligotrophication trajectories of these lagoons were still very vulnerable to occasional eutrophication events. On the other hand, the oligotrophic lagoon marginally responded to the enrichment, indicating its adaptation to nutrientdepleted conditions. We observed a shift along the eutrophication gradient, from a co-limitation by N and P in the oligotrophic and the mesotrophic lagoons to a single and strong N limitation in the hypertrophic lagoon. Each community demonstrated specific use of internal, external or recycled nutrient pools under experimentally induced limitation.

中文翻译：

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浮游植物利用不同富营养化状态并参与再贫营养化过程的沿海泻湖中的营养物质的策略

我们研究了中营养型和肥厚型地中海沿海泻湖，这两个泻湖同时经历了 9 年的营养输入减少。我们将这两个泻湖与一个贫营养的沿海泻湖进行了比较。使用包含添加磷和/或铵的 24 小时孵化的生物测定，我们研究了浮游植物群落对夏季期间生物量、大小等级结构、丰度和生长的营养富集的响应。对于氮和磷，我们确定了哪种养分限制了浮游植物的生长，以及社区采取了哪些养分开发策略来应对这些限制。超浮游植物在3个群落中占主导地位，但泻湖之间的组成不同。绿藻在肥厚的泻湖中占主导地位，而中营养泻湖则呈现出更高的浮游植物群多样性。Picocyanobacteria 和小硅藻是贫营养泻湖中最丰富的群体，尽管它们的生物量比绿藻少。中营养和肥厚泻湖的群落对营养脉冲做出强烈反应，表明这些泻湖的再贫营养化轨迹仍然非常容易受到偶尔的富营养化事件的影响。另一方面，贫营养泻湖对富集反应微乎其微，表明它适应了营养耗尽的条件。我们观察到沿富营养化梯度的转变，从贫营养和中营养泻湖中 N 和 P 的共同限制到肥厚泻湖中单一和强烈的 N 限制。