Microplastics (MPs) are ubiquitous in freshwater ecosystems and their accumulation has been considered an emerging threat. Early research on the effects of MPs on macrophytes primarily focused on the toxicological impacts on individual macrophytes, with several studies suggesting that lower concentrations of MPs have little impact on macrophytes. However, the ecological implications of lower MP concentrations on macrophyte communities remain largely unexplored. Here, we experimented to assess the effects of lower concentrations including 25 mg/L, 50 mg/L, 75 mg/L, and 100 mg/L of polyethylene (PE) microplastics on Spirodela polyrhiza and Lemna minor, and their community. Our results also indicated that PE concentrations below 100 mg/L had no significant effect on relative growth rate, specific leaf area, Chlorophyll a, Chlorophyll b, Chlorophyll a + b, carotenoid, malondialdehyde (MDA), catalase, and soluble sugar of monocultural S. polyrhiza. However, a lower concentration of PE significantly decreased the MDA of monocultural L. minor and significantly affected the comprehensive index of S. polyrhiza. These findings suggested that lower concentrations of PE can influence interactions between macrophytes maybe due to the cumulative effects of many weak interactions. Additionally, our study showed that 75 mg/L and 100 mg/L PE additions decreased the competitive balance index value of two macrophytes under mixed-culture condition. This result implied that the ecological influence of lower concentration MPs on macrophytes may manifest at the community level rather than at the population level, due to species-specific responses and varying degrees of sensitivity of macrophytes to PE concentrations. Thus, our study emphasizes the need to closely monitor the ecological consequences of emerging contaminants such as MPs accumulation on macrophyte communities, rather than focusing solely on the morphology and physiology of individual macrophytes.

中文翻译：

---

低浓度聚乙烯微塑料可以通过许多弱相互作用的综合作用来影响自由漂浮的大型植物相互作用：不可忽视的生态影响


微塑料 （MP） 在淡水生态系统中无处不在，其积累一直被认为是一种新出现的威胁。关于 MP 对大型植物影响的早期研究主要集中在对单个大型植物的毒理学影响上，几项研究表明，较低浓度的 MP 对大型植物的影响很小。然而，较低的 MP 浓度对大型植物群落的生态影响在很大程度上仍未得到探索。在这里，我们实验评估了较低浓度（包括 25 mg/L、50 mg/L、75 mg/L 和 100 mg/L 聚乙烯 （PE） 微塑料对多根螺旋藻和小藻及其群落的影响。结果表明，PE 浓度低于 100 mg/L 对单作多根茎的相对生长速率、比叶面积、叶绿素 a、叶绿素 b、叶绿素 a + b、类胡萝卜素、丙二醛 （MDA）、过氧化氢酶和可溶性糖没有显著影响。然而，较低浓度的 PE 显著降低了单一栽培小栔子的 MDA，并显著影响了多根沙门草的综合指数。这些发现表明，较低浓度的 PE 可以影响大型植物之间的相互作用，这可能是由于许多弱相互作用的累积效应。此外，我们的研究表明，在混合培养条件下，75 mg/L 和 100 mg/L PE 添加降低了两种大型植物的竞争平衡指数值。这一结果表明，由于物种特异性反应和大型植物对 PE 浓度的不同程度的敏感性，较低浓度 MP 对大型植物的生态影响可能表现在群落水平而不是种群水平。 因此，我们的研究强调需要密切监测新出现的污染物（如 MPS 在大型植物群落上的积累）的生态后果，而不是仅仅关注单个大型植物的形态和生理学。