Successful plant invasions are often explained by adaptation to novel environments. However, invasive species usually occupy broad niches within their native and introduced ranges. A true understanding of microevolution during invasion therefore requires a wide sampling of ranges, ideally with a knowledge of introduction history. We tested for genetic differentiation in herbivore resistance among 128 introduced (European, North American) and native (Chinese, Japanese) populations of the invasive Japanese knotweed (Reynoutria japonica) in two common gardens in the native range. In both common gardens, we found that the resistance traits of the introduced populations differed from most Chinese native populations but not from native populations in Japan, which are the two putative sources of introduction. Compared to Chinese populations, introduced European populations had thicker leaves in both common gardens with a lower C: N ratio but higher flavonoids content in the Shanghai garden. In the native range, variation in herbivore resistance was much more strongly associated with climate of origin than in introduced populations. Our results support that introducing particular resistance phenotypes from Japan played a key role in the invasion of knotweed into Europe and North America. Our study demonstrates how knowledge of introduction history can avoid misinterpretations of observed biogeographic divergence.

Rapid evolution contributes to plant invasion success. Previous studies have rarely considered the coevolution of multidimensional traits in invasive plants. We compared multiple traits related to growth, fecundity, and herbivore palatability of the widespread invader Spartina alterniflora in its native (US) and introduced (China) families across large geographic scales. Of 18 tested variables, ten revealed genetic-based differences between native and introduced ranges, and nine exhibited latitudinal clines within the introduced range. Introduced families compared to natives exhibited superior syndromes with larger growth, higher fecundity, and lower palatability, which were linked to provenance climates and could enhance plant competitiveness and spread. We conclude that within only 40 years since its introduction to China, Spartina has evolved an integrated ecological strategy to enhance invasiveness under climate selective pressure, making it the most successful invader along China’s coast. Our study underscores the importance of considering multivariate traits to understand plant invasion success.

Bryophytes’ remarkable capacity to tolerate extreme abiotic conditions allows us to enhance our understanding of the diversity of molecular mechanisms involved in plant stress response. Here, we used next generation sequencing to study DNA methylation and gene expression changes in plants from four populations of the metallophyte moss Scopelophila cataractae experimentally exposed to either Cd or Cu. These populations previously showed differences in tolerance to both metals, so here, we aimed at uncovering the molecular basis of this phenotypic differentiation. We found no evidence of genetic differentiation among the populations studied. The epigenetic data, however, showed limited but significant population-specific changes in DNA methylation in response to both metals. Exposure to acute Cu stress in the laboratory led to the downregulation of genes involved in heavy metal tolerance in both populations regardless of their tolerance level, but this response was quantitatively higher in the most tolerant. We propose that chronic exposure to varying levels of heavy metals in the field led to potentially non-genetically-based intraspecific differentiation for heavy metal tolerance in S. cataractae. The most tolerant plants invested more in constitutive protection and were more efficient in entering a conservative state when faced with acute Cu stress.

Phenotypic variation in natural populations is crucial for rapid adjustment to challenging environmental conditions such as exposure to heavy metal pollution. Hence, the study of variation in traits related to plant response to heavy metal stress provides valuable insight into the likelihood of a population’s survival. We investigate the patterns and mechanisms of intraspecific phenotypic variation for heavy metal accumulation and tolerance in bryophytes, one of the most resilient yet relatively understudied taxa. Two terrestrial mosses exposed to Cd and Cu in the laboratory, the heavy metal specialist Scopelophila cataractae and the facultative metallophyte Ceratodon purpureus, showed intraspecific differences in tolerance to these metals. Only the heavy metal specialist showed differences in accumulation which in the case of Cu could be associated to preferential relocation towards the stem to protect their main photosynthetic organs. We also report the first evidence for sexual dimorphism for Cd tolerance in C. purpureus (females being more tolerant than males). Our results provide support for high variation in the capacity of bryophytes to respond to environmental challenge despite potentially low levels of genetic variation and lack of previous exposure to stress, as well as evidence for metal-dependent, sex-specific differences in heavy metal tolerance in bryophytes.