Temporal fluctuations in water levels are important ecological driving forces in shallow aquatic ecosystems. Alterations to fluviometric levels are even more conspicuous after the construction of dams, and aquatic macrophytes respond with anatomical and morphological adaptations to such changes. We performed an experiment to analyse the anatomical responses of two common Neotropical species of emergent macrophytes (Polygonum ferrugineum and P. acuminatum) to water-level fluctuations. The experiment simulated three water-level variations: constant low water, constant deep water and fluctuating water levels (0.8-m oscillation/6 days; commonly caused by dam operation). We measured anatomical responses of roots (perimeter and number of the intercellular spaces), stems (perimeter and number of the intercellular spaces and cortical thickness) and leaves (palisade and lacunous parenchyma thickness). Water level affected all anatomical traits we measured and all increased when plants remained submerged (high-depth treatment). Compared with P. ferrugineum, P. acuminatum had higher values of both perimeter of the intercellular space in the roots and number of intercellular spaces in the stems. These results indicate that water-level fluctuations influence the anatomy of both species and that, compared with P. ferrugineum, P. acuminatum has greater plasticity and better tolerates submersion. These responses may be explained by the different survival strategies of each species when growing under submersion. Thus, our results reflect the different selective pressures from water levels experienced by these two species during their evolution.

中文翻译：

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蓼属两种挺水植物的解剖学响应水位波动的差异变化

水位的时间波动是浅水生态系统的重要生态驱动力。大坝建成后，水流测量水平的变化更加明显，水生大型植物对这种变化做出解剖学和形态学适应。我们进行了一项实验来分析两种常见的新热带植物新热带物种（Polygonum ferrugineum和P. acuminatum）的解剖学反应。) 到水位波动。实验模拟了三种水位变化：恒定低水位、恒定深水位和波动水位（0.8 米振荡/6 天；通常由大坝运行引起）。我们测量了根（细胞间隙的周长和数量）、茎（细胞间隙的周长和数量以及皮质厚度）和叶（栅栏和腔隙薄壁组织厚度）的解剖学反应。水位影响了我们测量的所有解剖特征，并且当植物保持在水下（深度处理）时，水位都会增加。相比P. ferrugineum，P.尖锐湿疣根中细胞间隙的周长和茎中细胞间隙的数量都具有较高的值。这些结果表明，水位波动影响这两个物种的解剖结构和，比P. ferrugineum，P.尖锐湿疣具有较大的可塑性和更好的容忍淹没。这些反应可能是由每个物种在淹没下生长时的不同生存策略来解释的。因此，我们的结果反映了这两个物种在进化过程中经历的来自水位的不同选择压力。