Germination dynamics and seedling frost resistance of invasive and native Impatiens species reflect local climatic conditions

Invasion of some alien plants is considered to be associated with inter-population differentiation and adaptations to local conditions. To obtain an insight into these processes it is convenient to compare invasive plants with their native congeners. The intra-specific differentiation during invasion was studied using four Impatiens (Balsaminaceae) species in Central Europe: native Impatiens noli-tangere and three aliens (highly invasive Impatiens glandulifera, less invasive Impatiens parviflora and potentially invasive Impatiens capensis). Differentiation in traits important for the establishment (germination; seedling emergence; seedling frost resistance) was measured in a laboratory and an experimental garden using seed collected from five natural populations of each species. Frost resistance of I. capensis, currently invasive in Western Europe, was within the scope of other congeners and it does not seem to be a barrier to spread of the species into Central Europe. Among-population differences were found within all species except I. capensis. In I. noli-tangere, I. glandulifera and I. parviflora the differences were related to the climatic characteristics in early spring at the source localities, which indicates that individuals may be adapted to local conditions. The differences found between the populations of I. noli-tangere, I. glandulifera and I. parviflora are likely to reflect the frost sensitivity of the species. In the highly frost-sensitive I. parviflora differentiation was found both in germination and frost resistance of individual populations. In I. glandulifera the differences among populations in frost sensitivity depended on temperature at the seed source and corresponded to the pattern of emergence of seedlings in the garden. In the native I. noli-tangere, the differences among populations in the time of germination depended on temperature at the seed-source locality. Since local adaptations were indicated both in native and invasive species studied, they are unlikely to provide the invasive Impatiens species with an advantage against the native congener, at least in terms of the traits investigated.