Data from: Phenotypic plasticity of invasive knotweed across Europe: a distributed common garden experiment

Successful large-scale biological invasions require introduced species to either rapidly adapt to a broad range of - partly novel - environmental conditions, or to possess a high level of phenotypic plasticity. Replicated common garden experiments across the introduced range provide a powerful framework to investigate these complementary mechanisms. To better understand population differentiation, adaptation and plasticity of invasive Japanese knotweed (Reynoutria japonica) in Europe, we compared the performance of knotweed plants from 46 European populations, collected across a 2000 km latitudinal transect, in three common gardens with contrasting climatic conditions, one at the southern edge, one in the center, and one at the northern edge of the species’ European distribution. The plants exhibited strong phenotypic plasticity across the three gardens, with a more acquisitive growth strategy in the southern garden, and a more conservative strategy and change of architecture in the climatically unfavorable north. Although we observed phenotypic selection on several leaf traits, with some differences in selection between the gardens, we found little evidence for population differentiation or local adaptation, i.e., variation in plant performance was not negatively related to climate or geographic distance. Greater plasticity in leaf thickness across gardens was linked to the production of fewer but larger shoots, indicating a trade-off between growth and clonal expansion. In addition, populations from higher latitudes and regions with greater inter-annual temperature variability displayed increased plasticity in shoot volume and shrubbiness, but reduced plasticity in shoot number. Our results suggest that local adaptation has not played a key role in the success of Japanese knotweed in Europe. Instead, its high overall phenotypic plasticity (‘general purpose genotype’), as well as evolutionary fine-tuning of plasticity, may have contributed to the species’ invasion success across a broad range of environments.成功的大规模生物入侵，要求外来物种要么能够快速适应广泛且部分为全新的环境条件，要么具备高水平的表型可塑性（phenotypic plasticity）。在入侵分布范围内开展的重复同质园实验，为探究这两类互补的入侵机制提供了强有力的研究框架。为深入解析入侵欧洲的日本虎杖（Reynoutria japonica）的种群分化、适应性及表型可塑性，我们选取沿2000公里纬度样带采集的46个欧洲种群的虎杖植株，在3个气候条件迥异的同质园中开展性能对比实验：这3个同质园分别位于该物种欧洲分布范围的南缘、中心区域与北缘。供试植株在3个同质园中表现出显著的表型可塑性：在南部同质园中其采取更为快速的资源获取型生长策略，而在气候条件不利的北部同质园中则转为更为保守的生长策略，并伴随株型结构的改变。尽管我们在多个叶片性状上观测到表型选择，且不同同质园间的选择强度存在一定差异，但几乎未发现种群分化或本地适应性的相关证据：即植株性能的变异与气候或地理距离并无负相关关系。叶片厚度在不同同质园间的较高可塑性，与植株产生更少但更粗壮的枝条相关，这表明生长与克隆扩张之间存在权衡关系。此外，来自高纬度地区以及年际温度变异性更高区域的种群，其枝条体积与灌丛化程度的可塑性有所提升，但枝条数量的可塑性则有所降低。本研究结果表明，本地适应性并非日本虎杖在欧洲成功入侵的关键驱动因素。相反，其整体高水平的表型可塑性（‘通用型基因型（general purpose genotype）’），以及对可塑性的进化微调，或许助力该物种在广泛的环境区间内实现入侵成功。