Invasive species are widely recognized as one of the primary direct contributors to biodiversity loss worldwide. Consequently, it is of global importance to understand the mechanisms underlying their invasion success.

Reynoutria japonica, also known as Japanese knotweed, is native to eastern Asia and is a highly invasive plant species in Europe and North America. The invasion of the species brings substantial damages to infrastructure and ecosystems, however, mechanisms of its high invasiveness are not fully understood.

In a study published in New Phytologist, an international team including researchers from where Japanese knotweed is native (China and Japan) and introduced (Germany and USA) investigated plants from large populations of this global plant invader, and elucidated the reasons behind its invasion success.

The growth and clonal reproduction of 128 Reynoutria japonica populations, 55 native-range populations (Japan and China) and 73 introduced-range populations (North America and Europe), were compared in two common gardens, one at Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and the other at Fudan University, both in China.

In terms of most characteristics, there was no significant difference between the introduced plants and those from the presumed native Japanese populations. Reynoutria japonica plants from all four ranges demonstrated almost equivalent aboveground biomass in both gardens. Interestingly, plants from China were taller and had fewer ramets than those from Japan, North America, and Europe, highlighting the broader differences within the native range of this species.

Besides, both introduced North American and European populations exhibited greater plasticity in terms of the number of ramets compared to the native Chinese populations, and they were more plastic in number of ramets than putative source populations in response to growing conditions of our common garden sites, suggesting an evolutionary shift towards increased clonality in the introduced ranges.

These findings indicated that the invasion success of Reynoutria japonica may be attributed to the introduction of a highly clonal genotype (general-purpose genotype) from Japan, and a build on post-introduction evolutionary shift of higher clonality.

“Our study demonstrates that the introduction of certain genotype and an evolutionary shift towards greater plasticity in clonality could have contributed to the large-scale colonization of Reynoutria japonica in new environments. It provides a good example for investigating mechanisms behind the phenotypic divergence of invasive plants across large biogeographic distribution,” said Dr. LIAO Zhiyong from XTBG, one correspondence author of this study. 

A photo of Reynoutria japonica population in the introduced range Europe. (Image by Dr. Madalin Parepa)