Temperature-dependent seedling development in native and alien herbaceous plants and associations with naturalization extent.

BACKGROUND AND AIMS: Temperature-dependent responses during early seedling development may contribute to variation in naturalization among herbaceous plants, yet experimental evidence remains limited. We compared how temperature affected leaf development in 123 dicotyledonous species native or alien to Central Europe and tested whether species-level temperature-dependent developmental metrics were associated with reported global naturalization extent. METHODS: We recorded the timing of appearance of the first five true-leaf stages (D1-D5) and calculated leaf appearance rate (LAR) in 64 native and 59 alien species grown at seven constant temperatures (10-34 °C). We tested the effects of temperature and alien status in 10,015 seedlings using Bayesian phylogenetic mixed models. We then derived three species-level developmental metrics, namely, Max LAR, temperature at Max LAR (T-max-LAR), and observed developmental temperature range (TWobs) and tested for differences between alien and native species and associations with naturalization extent, accounting for life history and seed mass. KEY RESULTS: Temperature strongly affected both the timing and rate of early leaf development. Alien species did not clearly differ from native species in the timing of first true-leaf appearance but showed modestly higher LAR from 22 to 34 °C. Max LAR was modestly higher in alien species and lower in perennials and larger-seeded species, while T-max-LAR and TWobs were similar in alien and native species. Greater naturalization extent was associated with higher Max LAR and wider TWobs, but not with T-max-LAR. CONCLUSIONS: Early post-germination development was strongly dependent on temperature, making this stage particularly relevant under climate warming. Although differences between alien and native species were modest, they became more evident at warmer temperatures and may thus become more important as temperatures experienced during recruitment increase. Associations with reported naturalization extent further suggest that temperature-dependent early development could become more relevant to naturalization of alien plants under a warming climate.