Phylogenetic relatedness confers competitive advantage of alien plants over natives under biotic stress

Plant invasions are increasingly being influenced by the complex interplay of global change factors (GCFs), notably biotic and abiotic stresses. However, how abiotic and biotic stresses affect the competitive performance of alien and native plants, as well as how phylogenetic relatedness regulates it, remains unclear. To test this, we selected six alien and six native confamilial plant species and grew them under abiotic (nutrient limitation) and biotic (enemy herbivory) stress treatments at three levels of plant interactions (no, intraspecific and interspecific). Herbivory more strongly reduced the biomass of native species than alien ones. Furthermore, under herbivory, alien species accumulated more biomass under interspecific competition than intraspecific competition, whereas natives exhibited no such difference. Meanwhile, alien plants had a greater positive correlation between biomass and phylogenetic distance than natives. We found that biotic stress favors aliens, particularly when they compete with distantly related plants. Our findings demonstrate that alien plants possess a competitive advantage over natives via biotic interactions, which is modulated by their phylogenetic distance. This advantage likely disrupts the coexistence of alien and native species, thereby facilitating the invasion of alien plants into biotically stressful environments.