Although phylogenetic distance between native and exotic species has a close link with their interactions, it is still unclear how environmental stresses and species interactions influence the relationship between phylogenetic distance and biological invasions. Here we assessed the effect of invader–native phylogenetic distance on the growth of the invader (Symphyotrichum subulatum) under three levels of drought (no, moderate, or intense drought). Under no drought, interspecific competition between close relatives was the dominant process and native communities more closely related to the invader showed higher resistance to invasion, supporting Darwin's naturalization hypothesis. In contrast, under intense drought, facilitation between close relatives by mutualism with arbuscular mycorrhizal fungi (AMF) became more important, and the invader became more successful in their more closely related native communities, supporting the preadaptation hypothesis. The colonization rate of AMF of the invader was higher in more closely related native communities regardless of the drought treatment, but it was only positively related to invader biomass under intense drought. Therefore, the shift of species interactions from competition to facilitation may be ascribed to the promotion of AMF to invasion occurring under intense drought, which leads to the effect of closely related natives on the invader shifting from negative to positive. Our results provide a new angle to resolve Darwin's naturalization conundrum from the change of species interactions along a stress gradient, and provide important clues for invasion management when species interactions change in response to global climatic change.

中文翻译：

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物种相互作用的变化调和了达尔文的归化难题

尽管本地和外来物种之间的系统发育距离与它们之间的相互作用有着密切的联系，但目前尚不清楚环境胁迫和物种相互作用如何影响系统发育距离与生物入侵之间的关系。在这里，我们评估了入侵者-本地系统发育距离对入侵者生长的影响（Symphyotrichum subulatum) 在三个干旱级别（无、中度或强烈干旱）下。在没有干旱的情况下，近亲之间的种间竞争是主导过程，与入侵者关系更密切的土著社区表现出更高的入侵抵抗力，支持达尔文的归化假说。相比之下，在严重干旱下，近亲之间通过与丛枝菌根真菌 (AMF) 的共生关系变得更加重要，入侵者在其关系更密切的本地社区中变得更加成功，这支持了预适应假说。无论干旱处理如何，入侵者 AMF 的定殖率在更密切相关的本地群落中更高，但它仅与强烈干旱下的入侵者生物量正相关。所以，物种相互作用从竞争到促进的转变可能归因于AMF促进了强烈干旱下的入侵，这导致密切相关的本地人对入侵者的影响从消极转变为积极。我们的研究结果为解决达尔文的物种相互作用沿应力梯度变化的归化难题提供了一个新的角度，并为物种相互作用随全球气候变化而变化时的入侵管理提供了重要线索。