Water level fluctuations (WLF), one of the most affected ecological drivers by climate change, are dominant forces controlling submerged macrophyte performance and distribution in freshwater ecosystems. Submerged macrophytes are prominent components of shallow lakes, predicting their response to WLF is therefore crucial for the management and conservation of these valuable and vulnerable ecosystems. We conducted an experiment in 15 outdoor mesocosms to explore the influence of WLF on the performance of Vallisneria spinulosa. We subjected V. spinulosa to WLF of two amplitudes and two frequencies, with stable water level as a control, and measured variations in 20 traits related with growth, sexual and asexual reproduction and resource allocation. Generally, compared with the control plants, fluctuations in water level adversely affected macrophyte biomass and growth, but increased both height and specific leaf area, which are helpful for adaptation of V. spinulosa to high-water level periods. Changes in the WLF frequency had little effect on the growth and reproduction of V. spinulosa plants apart from their leaf mass. In contrast, increased amplitude not only inhibited aboveground and root growth of V. spinulosa, but also decreased investment in sexual reproduction by influencing fruit production. V. spinulosa held a relatively stable allocation to overwintering asexual propagules in response to both components of WFL, which can maintain a capacity for clonal propagation following WLF. Moreover, as WLF amplitude increased, V. spinulosa invested a higher fraction of resources to belowground mass at the expense of their allocation to leaf mass. Our results suggest that shifts in WFL and especially magnified WLF amplitude due to climate change, may severely affect the growth and reproduction of submerged macrophytes with implications for other biota and the ecological state of shallow lakes.

中文翻译：

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水生植物苦草生长、繁殖和资源分配的变化：水位波动幅度和频率的影响

水位波动 (WLF) 是受气候变化影响最大的生态驱动因素之一，是控制淡水生态系统中沉水植物表现和分布的主要力量。淹没的大型植物是浅湖的重要组成部分，因此预测它们对 WLF 的反应对于管理和保护这些有价值和脆弱的生态系统至关重要。我们在 15 个室外中层环境中进行了一项实验，以探索 WLF 对苦木性能的影响。我们将 V. spinulosa 置于两个振幅和两个频率的 WLF 中，以稳定的水位作为对照，并测量了与生长、有性和无性繁殖以及资源分配相关的 20 个性状的变化。一般来说，与对照植物相比，水位波动对大型植物生物量和生长产生不利影响，但增加了高度和比叶面积，这有助于 V. spinulosa 适应高水位时期。除了叶片质量外，WLF 频率的变化对 V. spinulosa 植物的生长和繁殖几乎没有影响。相比之下，振幅的增加不仅抑制了刺五花的地上和根系生长，而且通过影响果实产量降低了对有性繁殖的投资。V. spinulosa 对越冬无性繁殖体的分配相对稳定，以响应 WFL 的两个组成部分，这可以在 WLF 后保持克隆繁殖的能力。此外，随着 WLF 幅度的增加，V. spinulosa 将更高比例的资源投入到地下物质中，而牺牲了它们在叶片中的分配。我们的研究结果表明，WFL 的变化，尤其是由于气候变化而放大的 WLF 幅度，可能会严重影响沉水植物的生长和繁殖，并对其他生物群和浅湖的生态状态产生影响。