Invasive aquatic plants constitute a great problem in many freshwater systems. Although many studies have addressed the potential threats of invasion by exotic species in aquatic ecosystems, few studies have considered the interactions (competition, facilitation, coexistence) between exotic aquatic plants of similar growth form in invaded communities. Our aim was to investigate experimentally the effect of density in monocultures and the effect of neighbour identity and plant density on a focal species in mixed cultures. We used Elodea canadensis, Egeria densa and Lagarosiphon major as model species and conducted two experiments, one in a monoculture and another in a mixed culture following an additive design. Individuals were planted in pots with several treatments based on the identity and density of neighbour species. Our results demonstrated that the development of an invasive submerged plant could be influenced either positively (facilitation) or negatively (competition or inhibition) by the presence of more than one neighbour species of different densities. An increase in density significantly stimulated competition intensity, although the effect of density on the performance of the invader also depended on neighbour identity. A facilitative effect of E. canadensis on the apical growth of E. densa was established. However, despite these results, the competitive outcome also depended on other environmental factors (e.g. underwater radiation), not on plant density and neighbour identity alone.

中文翻译：

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密度和邻居对相似生长形式的入侵植物之间相互作用的影响

在许多淡水系统中，入侵性水生植物构成了一个很大的问题。尽管许多研究已经解决了外来物种入侵水生生态系统的潜在威胁，但很少有研究考虑到入侵社区中具有相似生长形式的外来水生植物之间的相互作用（竞争，促进，共存）。我们的目的是通过实验研究密度在单一文化中的影响以及邻居身份和植物密度对混合文化中的焦点物种的影响。我们用伊乐藻，水蕴草和Lagarosiphon重大作为模型物种，并进行了两个实验，一个是在单培养中，另一个是在添加设计后的混合培养中。根据邻近物种的身份和密度，将个体种植在盆中并进行多种处理。我们的研究结果表明，存在一种以上密度不同的邻近物种，可以对入侵性淹没植物的发育产生积极（促进）或消极（竞争或抑制）影响。密度的增加极大地刺激了竞争强度，尽管密度对入侵者性能的影响也取决于邻居的身份。加拿大E.ensis对E. densa根尖生长的促进作用建立了。但是，尽管取得了这些结果，但竞争结果还取决于其他环境因素（例如水下辐射），而不仅取决于植物的密度和邻居身份。