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Keywords:

  • Biological invasions;
  • common garden experiment;
  • comparative study;
  • invasive plants, phenotypic plasticity;
  • shade avoidance;
  • shade treatment;
  • tolerance

Abstract

Aim  Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non-invasive species differ in presumably adaptive plasticity.

Location  Europe (for native species); the rest of the world and North America in particular (for alien species).

Methods  We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non-shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance.

Results  Invasive species had higher shoot–root ratios, tended to have longer leaf-blades, and produced more biomass than congeneric non-invasive species both under shaded and non-shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade-induced responses, which are widely considered to be adaptive, did not differ between invasive and non-invasive species.

Main conclusions  We conclude that high biomass production across different light environments pre-adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured.