Climate warming and water primroses: Germination responses of populations from two invaded ranges

• Germination capacity of two Ludwigia congeners was tested at 24 and 27 °C.
• Five of the ten tested populations reached final germination percentages >80%.
• Germination patterns of L. hexapetala depend on geographical origin of the seeds.
• The 3 °C warming treatment accelerated the time to germination.
• It also increased germination percentage of L. hexapetala populations from France.

Environmental temperature is the primary regulator of germination. Global climatic warming may substantially change seed dormancy and germination responses of wetland and riparian plant species. The potential for increased germination capacity, seed dispersal and geographic range expansion of invasive plant species is a particular concern relevant to the conservation of native biodiversity. The aim of this study was to compare the germination capacity of Ludwigia hexapetala and Ludwigia peploides subsp. montevidensis from two invaded ranges under 3 °C warming predicted in climate change models. Germination of seeds collected from two invaded ranges was tested in controlled conditions at two air temperature regimes, 24 °C/14 °C and 27 °C/17 °C. Regardless of temperatures, the germination rates of studied species were greater than 80% for L. hexapetala from California, and for two populations of L. peploides from France. Seeds of L. hexapetala from California germinated two-fold more than seeds from France, while L. peploides from California germinated less quickly and at lower rates than two of three populations from France. The variation observed between invaded ranges could be interpreted as an adjustment of the germination responses of water primroses populations due to provenance environmental characteristics. The 3 °C warming treatment accelerated the time to germination of water primrose seeds from California and France, and was a driving factor in final germination percentage for L. hexapetala populations from France. This study confirms that sexual reproduction can contribute to invasiveness of Ludwigia spp. and germination capacity will be maintained with 3 °C temperature warming.