■淡水生态系统由于其连通性和各种植物扩散载体而容易受到外来大型植物的入侵。这些生态系统经常经历人为的营养富集,有利于有效利用这些资源的入侵物种。繁殖压力(反映引入个体的数量)和栖息地入侵性是入侵成功的关键决定因素。此外,敌人释放假说预测逃离天敌,比如食草动物,允许外来物种投资更多的资源用于生长和繁殖,而不是防御,增强他们的侵入潜力。然而,传播压力的综合影响,食草动物,由于缺乏研究,对入侵外来大型植物和本地大型植物群落之间竞争动态的营养富集还没有得到很好的理解。
■我们进行了全因子中观实验,以探索草食动物的个体和综合作用,营养水平,传播压力,以及外来大型植物Myriophyllumaquaticum入侵成功进入包含Vallisnerianatans的天然大型植物群落的竞争,平顶草,和肉豆蔻。此设置包括不同的M.aquaticum密度(低与高,模拟低和高传播压力),本地蜗牛Lymnaeastagnalis的两个食草动物水平(食草动物与无食草动物),和两种营养条件(低与高)。在没有天然大型植物竞争的情况下,两个密度的Myriophylumaquaticum也分别生长。
■当同时经受高密度种内竞争条件时,入侵的外来大型水生植物M.aquaticum产生的芽和总生物量最高,没有食草动物,和低营养可利用性治疗。此外,在营养丰富的条件下,水分枝杆菌的高繁殖压力显着降低了天然大型植物群落的生长,但是在营养贫乏的条件下没有观察到这种影响。
■这些发现表明,水草分枝杆菌具有适应性特征,使其能够在没有食草动物(支持敌人释放假说)的情况下以及在具有挑战性的环境中蓬勃发展,例如激烈的种内竞争和低养分利用率。此外,研究结果表明,当大量存在时,水生植物能显著抑制天然大型植物群落的生长,特别是在营养丰富的环境中。因此,降低水草的繁殖压力可以帮助控制其传播并减轻其生态影响。总的来说,这些发现强调外来入侵植物的生长和影响在不同的生境条件下可能会有所不同,并且是由生物和非生物因素的相互作用决定的。
UNASSIGNED: Freshwater ecosystems are susceptible to invasion by alien macrophytes due to their connectivity and various plant dispersal vectors. These ecosystems often experience anthropogenic nutrient enrichment, favouring invasive species that efficiently exploit these resources. Propagule pressure (reflecting the quantity of introduced individuals) and habitat invasibility are key determinants of invasion success. Moreover, the enemy release hypothesis predicts that escape from natural enemies, such as herbivores, allows alien species to invest more resources to growth and reproduction rather than defense, enhancing their invasive potential. Yet, the combined impact of propagule pressure, herbivory, and nutrient enrichment on the competitive dynamics between invasive alien macrophytes and native macrophyte communities is not well understood due to a paucity of studies.
UNASSIGNED: We conducted a full factorial mesocosm experiment to explore the individual and combined effects of herbivory, nutrient levels, propagule pressure, and competition on the invasion success of the alien macrophyte Myriophyllum aquaticum into a native macrophyte community comprising Vallisneria natans, Hydrilla verticillata, and Myriophyllum spicatum. This setup included varying M. aquaticum densities (low vs. high, simulating low and high propagule pressures), two levels of herbivory by the native snail Lymnaea stagnalis (herbivory vs no-herbivory), and two nutrient conditions (low vs. high). Myriophyllum aquaticum was also grown separately at both densities without competition from native macrophytes.
UNASSIGNED: The invasive alien macrophyte M. aquaticum produced the highest shoot and total biomass when simultaneously subjected to conditions of high-density intraspecific competition, no herbivory, and low-nutrient availability treatments. Moreover, a high propagule pressure of M. aquaticum significantly reduced the growth of the native macrophyte community in nutrient-rich conditions, but this effect was not observed in nutrient-poor conditions.
UNASSIGNED: These findings indicate that M. aquaticum has adaptive traits enabling it to flourish in the absence of herbivory (supporting the enemy release hypothesis) and in challenging environments such as intense intraspecific competition and low nutrient availability. Additionally, the findings demonstrate that when present in large numbers, M. aquaticum can significantly inhibit the growth of native macrophyte communities, particularly in nutrient-rich environments. Consequently, reducing the propagule pressure of M. aquaticum could help control its spread and mitigate its ecological impact. Overall, these findings emphasize that the growth and impacts of invasive alien plants can vary across different habitat conditions and is shaped by the interplay of biotic and abiotic factors.