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Achene traits involved in the water dispersal of the invasive Fallopia × bohemica complex: Variability and dispersal strategies
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International audience. Secondary dispersal of terrestrial plant species through watercourses increases the dispersal range of floating seeds but their exposure to water may also challenge their viability and colonisation potential. Many terrestrial invasive species benefit from watercourses to extend their invasive range because water exposure can favour seed germination and early survival of seedlings for species sensitive to dry conditions and water flow enhances their dispersal distance downstream. Floatability, germination rate and survival after water exposure are seed traits involved in water dispersal and their variability may lead to different dispersal strategies. To address the question of the variability of achene traits involved in dispersal, we experimentally measured these three traits for Fallopia × bohemica achenes collected from 10 different stands. The floatability of achenes varied between stands from 2.5 to 5 days and their germination in water extended this period to 20 days through the emergence of floating seedlings. Germination proportions also differed between stands from 0.3 to 0.95 and were negatively related to the median germination time. Seedling survival after planting in soil was affected by their exposure time. This effect differed between stands, but a short germination time did not explain a better survival of some stands. These results show that achenes may differ in their dispersal potential in terms of floatability, as well as tolerance of seedlings to water exposure during dispersal. This study also highlights the fact that achenes of some stands present a combination of traits particularly adapted to long distance dispersal through watercourses, which can contribute to the extension of the invaded area.
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