Plant invasion initiates with the establishment of an alien species population that begins interacting with the existing community in the invaded habitat. Competitive ability may confer advantage to invasive species during establishment. Autopolyploidy has been shown to significantly contribute to successful invasion of China by Solidago canadensis that is native to North America. But how polyploidization improves competitive ability and determines the dominance of invasive species when competing with a plant community in the introduced range remains unclear. Here, we manipulated the initial plant composition of plowed land and subsequently allowed natural colonization by S. canadensis in a five‐year common garden experiment. Diploid, tetraploid and hexaploid populations collected in North America (native range) and East Asia (introduced range) were separately planted and allowed to compete with associated weeds in individual plots. The diversity and compositional variation of the plant communities and the growth characteristics of S. canadensis were investigated in summer and autumn each year. Based on how the community assembled, three outcomes were found: 1) S. canadensis outcompeted local vegetation: tetraploids and hexaploids from the introduced range outcompeted associated weeds and were dominant at equilibrium; 2) S. canadensis coexisted with local vegetation: hexaploids from the native range were competitive but ultimately could not outcompete the local vegetation; and 3) S. canadensis became extinct: diploids from both the native and introduced ranges and tetraploids from the native range went extinct. Concomitantly, diversity was low in the first group and high in the second and third. Therefore, polyploidization contributes to the pre differentiation of competitive ability among native S. canadensis populations, facilitatating the invasion of China by this species. The competitive ability of polyploids was enhanced through possible rapid post introduction evolution after their introduction into China, which could be the crucial factor for successful invasion by S. canadensis.

driven range expansion of a temperate-originated plant to pan-tropic under global change. Ecological Monographs 91(2):e01445.

Solidago canadensis, originating from the temperate region of North America, has expanded southward to subtropical regions through polyploidization. Here we investigated whether freezing tolerance of S. canadensis was weakened during expansion. Measurement of the temperature causing 50% ruptured cells (LT 50 ) in 35 S. canadensis populations revealed ploidy-related differentiation in freezing tolerance. Freezing tolerance was found to decrease with increasing ploidy. The polyploid populations of S. canadensis had lower ScICE1 gene expression levels but more ScICE1 gene copies than the diploids. Furthermore, more DNA methylation sites in the ScICE1 gene promoter were detected in the polyploids than in the diploids. The results suggest that promoter methylation represses the expression of multi-copy ScICE1 genes, leading to weaker freezing tolerance in polyploid S. canadensis compared to the diploids. The study provides empirical evidence that DNA methylation regulates expression of the gene copies and supports polyploidization-driven adaptation to new environments. K E Y W O R D S

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