The invasive Australian swamp stonecrop, Crassula helmsii, is a perennial amphibious herb originating from Australia and New Zealand. In freshwater wetlands of North-western Europe, this alien plant species is invasive due to its efficient colonization of empty niches. The establishment of dense C. helmsii growth is threatening native biodiversity and functioning of freshwater ecosystems, especially oligotrophic wetlands with high disturbance and nutrient enrichments. As the effects of these potential drivers of ecosystem degradation are generally difficult to determine in the field, we tested the competitive strength of C. helmsii in a greenhouse experiment with two native competitor species of the same habitat type, Pilularia globulifera and Littorella uniflora. Sods dominated by either of the native species, as well as bare soils, were collected from the field and manually infested with propagules of C. helmsii. Settlement and growth of C. helmsii was assessed after five weeks. In addition, the effect of nutrient enrichment by water bird feces on competition was studied by adding waterfowl droppings. C. helmsii was able to settle successfully in all treatments, but P. globulifera and L. uniflora dominance reduced settlement success and growth of C. helmsii. On vegetated sods, the addition of waterfowl droppings had a low effect on the performance of C. helmsii, however, this treatment significantly increased biomass production on bare soils with low nutrient availability. We conclude that both absence of native competitors and eutrophication, including guanotrophication by waterfowl, explain the establishment success and invasiveness of C. helmsii. Given the fact that eradication of C. helmsii is very challenging, our results imply that management should focus on a combination of increasing local species densities and abating eutrophication. This will strongly limit the window of opportunity for invasion of C. helmsii and enhance resistance by native plant communities.

侵入性澳大利亚沼泽景天属景天树（Crassula helmsii）是一种多年生的两栖草本，起源于澳大利亚和新西兰。在西北欧的淡水湿地中，这种外来植物物种因其对空位的有效繁殖而受到入侵。密集的赫氏梭菌生长的建立正威胁着当地的生物多样性和淡水生态系统的功能，特别是营养紊乱和营养丰富的贫营养湿地。由于通常很难在田间确定这些潜在的生态系统退化驱动因素的影响，因此我们在温室实验中使用了两个相同栖息地类型的本地竞争物种Pilularia globulifera来测试了Helmsii的竞争强度。和独花小豆。从田间收集了以任何一种本地物种和裸露土壤为主的草皮，并人工感染了赫氏梭菌的繁殖体。五周后评估赫氏梭菌的沉降和生长。此外，还通过添加水禽粪便研究了水禽粪便对营养的富集对竞争的影响。C. helmsii能够在所有处理中成功定居，但是P. globulifera和L. uniflora优势降低了C. helmsii的定居成功和生长。在有植物的草皮上，添加水禽粪便对黑麦草的性能影响不大但是，这种处理显着增加了养分利用率低的裸露土壤的生物量生产。我们得出的结论是，缺乏本地竞争者和富营养化，包括水禽造成的营养化，都可以解释Helicii的建立成功和入侵性。鉴于消除赫氏梭菌的挑战非常艰巨，因此我们的结果表明，管理应侧重于增加本地物种密度和减少富营养化。这将极大地限制入侵Helmsii的机会之窗，并增强本地植物群落的抵抗力。