Genetic variability modulates the effect of habitat type and environmental conditions on early invasion success of Ailanthus altissima in Mediterranean ecosystems

At the early stages of an invasion by an exotic species, there are diverse environmental and genetic factors that limit its expansion. Ailanthus altissima is a tree from China and northern Vietnam which has become an invasive species in numerous ecosystems around the word. Our objective was to identify the relative effect of both genetic and environmental factors and how they interact with the emergence and early establishment of this invasive tree under Mediterranean conditions. To achieve this, seed germination and early establishment from different maternal sources were analyzed under contrasted environmental conditions in a series of experiments, using both laboratory and field approaches. Seed germination and early survival were affected by environmental factors such as habitat-type, the percentage of bare soil and climatic conditions (rainfall pulses), although the influence of these factors changed depending on the maternal source. Our study reveals that the genetic component affected not only the performance of A. altissima, it also modulated its response to environmental factors, which seemed to be the main drivers of germination and early establishment for this species. Our results highlight the importance of considering both genetic and environmental factors when studying plant invasion risk and success, and may be helpful in predicting and reducing the spread of this species in Mediterranean ecosystems.