Data from: Climate and rapid local adaptation as drivers of germination and seed bank dynamics of Alliaria petiolata (garlic mustard) in North America

Local differences in climate conditions may facilitate rapid evolutionary changes in introduced plants to optimize timing of germination or ability to survive in seed banks, which may constitute beneficial demographic adaptations during range expansions. Understanding differences in germination requirements and emergence patterns across a species’ range is critical for demographic modelling and potential invasive species control efforts.
We assessed germination responses of Alliaria petiolata using seeds collected from 10 populations spanning much of the North American distribution of the species. We compared germination responses under different stratification regimes in a growth chamber over 2·5 years, and evaluated seedling emergence in a common garden in Ithaca, New York over 13 years. We further evaluated how climate overlap between Ithaca and original collection sites influenced emergence patterns.
In the laboratory, germination of all populations was similar and highest at 4 °C stratification. Seeds exposed to sub-zero temperatures delayed germination and population responses were variable. In the common garden, seedlings from most populations emerged over 13 years, and emergence patterns were strongly influenced by population. Annual emergence was positively correlated with spring temperature and inversely correlated with number of spring days with minimum temperature below freezing. Climate overlap between the common garden and original collection location enhanced germination, but common garden climate conditions over the course of the 13-year experiment and population identity had greater explanatory power.
Synthesis. Laboratory germination tests did not reflect seedling emergence under field conditions. After 150 years of residence time in North America, Alliaria petiolata populations have developed striking differences in their responses to local climates and stratification requirements suggesting that a complex interplay of pre-adaptation, rapid evolutionary changes, and phenotypic plasticity result in locally adapted populations.

气候条件的区域差异可推动外来植物发生快速演化，使其优化萌发时机或种子库存活能力，这一过程在物种分布范围扩张阶段，或可形成有益的种群动态适应策略。解析物种分布区内的萌发需求与出苗模式差异，对种群动态建模及潜在入侵物种防控工作均具有关键意义。

本研究以覆盖蒜芥（Alliaria petiolata）北美大部分分布区的10个种群的种子为材料，评估其萌发响应。我们在人工气候箱内设置不同层积处理条件，开展了为期2.5年的萌发响应对比实验，并在纽约州伊萨卡的同质园实验圃中开展了为期13年的幼苗出苗监测。此外，我们还分析了伊萨卡与原始采集点之间的气候重叠度如何影响出苗模式。

实验室实验结果显示，所有种群的萌发率均以4℃层积处理下最高，且不同种群间萌发率差异不大；经亚低温处理的种子萌发进程延迟，且不同种群的响应存在显著差异。同质园监测结果表明，多数种群的幼苗可在13年的实验周期内出苗，且出苗模式受种群来源的影响极强。年出苗率与春季气温呈正相关，与春季最低气温低于0℃的天数呈负相关。同质园与原始采集点之间的气候重叠度可提升萌发效果，但13年实验期间同质园的气候条件以及种群来源，对出苗模式的解释力更强。

综合结论：实验室萌发实验无法反映野外条件下的幼苗出苗情况。蒜芥在北美定居已有150年之久，其不同种群对本地气候与层积需求的响应已产生显著差异，这表明预适应、快速演化与表型可塑性之间的复杂互作，共同塑造了具有本地适应性的种群。