Germination ecology of Phytolacca americana L. in its invasive range

Invasive species are a worldwide problem, and the germination process is useful to understand the characteristics that allow alien species to be invasive and their projected response to global climate change. Phytolacca americana is one of the most invasive plants in Italy, and we tested, for different populations (from different altitudes) how light, temperature, and cold stratification affect seed germination. According to our analyses, P. americana produces an exceptionally high number of seeds that may potentially survive in soil for extended periods. Seeds subjected to cold stratification and exposed to warmer temperatures, both in light and darkness, exhibited faster germination, with a higher germination rate and a shorter T50. Seeds collected at the highest elevation (337 m a.s.l.) have germinated in all tested thermal conditions, albeit with a lower germination percentage and a longer T50 compared with seeds collected at lower elevations (5 and 50 m a.s.l.) and tested under warm and moderate temperatures. In general, P. americana seems to adapt to moderate-warm temperatures (at low elevations) and moderate-cool temperatures (at highest elevations) and appears to increase germination with seeds exposed to cold stratification. These results, in a scenario of climate change, show that the invasiveness of P. americana may increase in the future.