Rapid adaptive evolution and phenotypic plasticity are two mechanisms that often underlie invasiveness of alien plant species, but whether they can co-occur within invasive plant populations under altered environmental conditions such as nitrogen (N) enrichment has seldom been explored. Latitudinal clines in plant trait responses to variation in environmental factors may provide evidence of local adaptation. Here, we inferred the relative contributions of phenotypic plasticity and local adaptation to the performance of the invasive plant Ambrosia artemisiifolia under different soil N levels, using a common garden approach. We grew A. artemisiifolia individuals raised from seeds that were sampled from six invasive populations along a wide latitudinal cline in China (23°42' N to 45°43' N) under three N (0, 5, and 10 g N m-2 ) levels in a common garden. Results show significant interpopulation genetic differentiation in plant height, number of branches, total biomass, and transpiration rate of the invader A. artemisiifolia across the N treatments. The populations also expressed genetic differentiation in basal diameter, growth rate, leaf area, seed width, root biomass, aboveground biomass, stomatal conductance, and intercellular CO2 concentration regardless of N treatments. Moreover, plants from different populations of the invader displayed plastic responses in time to first flower, hundred-grain weight, net photosynthetic rate, and relative biomass allocation to roots and shoots and seed length under different N treatments. Additionally, individuals of A. artemisiifolia from higher latitudes grew shorter and allocated less biomass to the roots regardless of N treatment, while latitudinal cline (or lack thereof) in other traits depended on the level of N in which the plants were grown. Overall, these results suggest that rapid adaptive evolution and phenotypic plasticity in the various traits that we quantified may jointly contribute to invasiveness of A. artemisiifolia under different levels of N availability. More broadly, the results support the idea that phenotypic plasticity and rapid adaptive evolution can jointly enable invasive plants to colonize a wide range of environmental conditions.
快速适应进化和表型可塑性是阐释外来植物入侵的两个机制，但是它们是否可以在变化的环境条件下(比如氮富集)同时作用于入侵种群，这方面的研究还不多。植物性状对环境因子变化响应的纬度趋势可能提供了局域适应的证据。本文采用同质园实验的方法，探究表现可塑性和局域适应对入侵植物豚草(Ambrosia artemisiifolia)在不同土壤氮水平下表现的相对贡献。我们沿中国纬度梯度(23°42′ N-45°43′ N)收集六个豚草入侵种群的种子，分别设置三个氮水平(0，5以及10 g N m−2 )种植在同质园中。结果表明，在不同的氮水平下，入侵豚草的株高、分枝数、总生物量和蒸腾速率存在显著的种群间遗传差异。在三种氮处理水平下，基径、生长速率、叶面积、种子宽度、根生物量、地上生物量、气孔导度和胞间二氧化碳浓度在种群间也存在遗传分化。在不同的氮处理下，来自不同种群的豚草植株在开花时间、百粒重、净光合速率、根冠比以及种子长度上表现出可塑性响应。此外，在所有氮处理水平下，来自更高纬度种群的豚草个体株高较小，分配到根部的生物量较少，而其他性状的纬度差异取决于氮处理水平。总之，研究结果表明，我们测量的各种性状中的快速适应性进化和表型可塑性可能联合作用，共同促进豚草在不同的氮水平下的入侵。广而言之，研究结果支持表型可塑性和快速适应性进化可以共同促进入侵植物在不同环境条件下定殖。.
Keywords: N addition; common garden; common ragweed; plant invasion; plasticity; population differentiation.
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