Alien species in urban areas have a large effect on overall species diversity. A suitable metric of flora’s response to environmental change is functional diversity (FD) that refers to the multivariate space of species’ trait compositions, reflecting their ecological niches. We studied how FD changed over 320 years of urbanization in the city of Halle (Saale), Germany. Selected functional traits (related to stress-tolerance, reproduction, competitiveness and phenology) were examined for the difference in FD between native and alien plant species, the latter specifically for archaeophytes, neophytes and invasive species. Functional diversity for each trait was calculated using Rao’s Q index followed by a linear model to test for changes in Rao’s Q over time between the groups. Over the 320 years, overall FD remained constant despite species turnover, but FD significantly increased for neophytes and invasive species compared to native species. Plant height was the only trait showing increase in FD as main effect, while for the other traits examined FD decreased over time. Considering invasive species separately, the majority of traits exhibit a significant increase in FD except for seed mass where it decreased. Finally, FD of multiple functional traits combined decreased over time. This can be due to homogenization of functional trait between native and alien species, as a consequence of habitats becoming more similar and subsequent habitat filtering. Our results demonstrate that during the last three centuries, urbanization influenced plant FD in various ways and may contribute to future uniformity of urban floras and greater invasiveness.

城市地区的外来物种对总体物种多样性影响很大。功能区系（FD）是植物对环境变化做出反应的合适度量，它是指物种特征组成的多元空间，反映了它们的生态位。我们研究了德国哈雷市（Saale）在320年的城市化过程中FD的变化。检查了选定的功能性状（与胁迫耐受性，繁殖，竞争力和物候有关）的本地植物物种与外来植物物种之间的FD差异，后者专门针对古生植物，新植物和入侵物种。使用Rao's Q指数和线性模型计算每个性状的功能多样性，以测试两组之间Rao's Q随时间的变化。在320年的时间里，尽管有物种更新，但总体FD保持恒定，但与原生物种相比，新生植物和入侵物种的FD显着增加。株高是唯一显示FD增加的主要性状，而对其他性状而言，FD随时间下降。单独考虑入侵物种，除种子质量下降外，大多数性状均表现出FD显着增加。最后，多种功能性状的总FD随时间降低。这可能是由于生境变得更加相似并随后进行了生境过滤而导致的本地和外来物种之间的功能性状均质化。我们的结果表明，在过去的三个世纪中，城市化以各种方式影响着植物的FD，并可能有助于未来城市植物区系的统一和更大的入侵性。