Role of traits, plasticity and local differentiation in plant invasions: Comparison of three balsam (Impatiens) species with different invasion status with their native congener

Background/Question/Methods

Species traits, plasticity, and local differentiation are assumed to affect the success of invasive plants, but these factors are mostly studied separately. To compare their role in plant invasions, we used four Impatiens (Balsaminaceae) species occurring in Central Europe: native I. noli-tangere, highly invasive I. glandulifera, less invasive I. parviflora, and potentially invasive I. capensis. By using closely related species coexisting in their habitats we minimized phylogenetic and habitat-related biases. We investigated germination timing, seedling appearance, their frost resistance, response to environmental factors (levels of nutrient availability, water supply, and irradiance) and competition in climatic chambers and an experimental garden, as well as seed banks and micro-site preferences in the field.

Results/Conclusions

We found differences in the performance of species and their populations. The pattern of germination timing of the species studied reflects spring temperatures in the original localities from which the seeds were collected, indicating thus local adaptations. The invasion success of the highly invasive I. glandulifera is supported by early and synchronised emergence of the seedlings, their large plasticity and large adults. Considerable local differentiation was found in juvenile stages of I. parviflora. The native species I. noli-tangere possesses some traits that allow it to persist in localities, such as formation of a short-term seed bank, comparably high frost resistance, ability to exploit high nutrient levels, good performance in shade, and tolerance to low levels of nutrients. Response of the species studied to water levels and simulated canopy shade is in accordance with their different micro-site preferences in the field, indicating that coexistence is possible but limited. The performance of I. capensis was within the scope of the other congeners; this species therefore does not seem to be constrained by micro-site conditions in central Europe and its future invasion cannot be excluded.