1. In shallow lakes, submerged macrophytes can stabilise clear‐water conditions and prevent phytoplankton blooms. Nutrient enrichment can promote their abundance. Above critical thresholds in water nutrient concentrations, however, submerged macrophytes have collapsed in many lakes worldwide with negative consequences for important ecosystem functions. The mechanisms behind this decline are complex and subject to debate.
2. We conducted mesocosm and laboratory experiments to investigate the top‐down effect of invasive herbivorous snails (Pomacea canaliculata) on native submerged macrophytes (Vallisneria natans) under low and moderate nutrient treatment. We tested whether effects of nutrient addition to the water column on snail herbivory were influenced by shading by phytoplankton and epiphyton, macrophyte elemental tissue content and snail nutrient release.
3. We found that herbivorous snails had strong negative top‐down effects on macrophytes, which were amplified by nutrient enrichment in the water column leading to higher macrophyte consumption rates. In moderate nutrient treatment, macrophyte consumption was faster and snails grew better than in low nutrient treatment. Additionally, snail treatments had higher nitrogen concentrations in the water leading to a negative feedback loop.
4. Our results suggest that snail herbivory may increase the chance for macrophyte collapse and shifts of shallow lakes to turbid states, and this effect occurs at lower snail densities when nutrient concentrations increase. Shallow lakes are thus severely at risk from projected increases in nutrient loading and spread of invasive herbivorous molluscs.

中文翻译：

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浅水湖泊处于危险之中：营养性富集通过侵入性草食蜗牛增强自上而下的控制

1. 在浅水湖泊中，淹没的大型植物可以稳定清水条件，并防止浮游植物开花。营养丰富可以促进它们的丰度。但是，超过水养分浓度的临界阈值，淹没的大型植物在世界各地的许多湖泊中倒塌，对重要的生态系统功能产生负面影响。这种下降背后的机制是复杂的，尚有争议。
2. 我们进行了中观和实验室实验，研究了在低和中度养分处理下侵袭性草食蜗牛（Pomacea canaliculata）对天然淹没植物（Vallisneria natans）的自顶向下作用。我们测试了浮游植物和附生植物的遮荫，大型植物元素组织含量和蜗牛养分释放是否影响了向水草中添加养分对蜗牛食草的影响。
3. 我们发现草食蜗牛对大型植物具有强烈的自上而下的负面影响，水柱中的养分富集进一步放大了大型植物的食用率。在中等营养水平下，与低营养水平相比，大型植物的消耗更快，蜗牛生长更好。此外，蜗牛处理后水中的氮浓度较高，从而导致负反馈回路。
4. 我们的研究结果表明，蜗牛的食草性可能增加大型植物崩溃和浅湖向浑浊状态转变的机会，当营养物浓度增加时，这种影响发生在蜗牛密度较低的情况下。因此，预计营养物负荷的增加和侵入性草食性软体动物的扩散会严重威胁浅湖。