Response of Native Grassland Plants to Ageratina adenophora Stress: Seedling Growth Inhibition and Antioxidant Defense

Ageratina adenophora is a highly aggressive weed that originates from central Mexico and Costa Rica. It has invaded and become naturalized across tropical and subtropical regions, posing significant challenges for biodiversity conservation and ecological restoration. While substantial research has revealed its impacts on diverse ecosystems and enhanced understanding of its phytotoxicity, investigations in grassland landscapes remain limited. Consequently, this study focused on Chengjiang County in southwestern China, a region heavily invaded by A. adenophora. Based on a preliminary survey, five grassland plant species that commonly co-occur and compete with it were assessed through seedling growth bioassays and physiological measurements conducted under the treatments of its aqueous tissue extract. The findings revealed that the recipient plants exhibited dynamic changes dependent on concentration. Specifically, there was a negative correlation between the content of malondialdehyde (MDA) and proline (Pro) and seedling height as well as root length (p < 0.05; p < 0.01). This suggests that higher extract concentrations triggered more pronounced stress-related cellular responses, which were concurrently associated with diminished seedling growth. Notably, Saccharum arundinaceum demonstrated the most significant elevation in peroxidase (POD) and catalase (CAT) activities, along with the highest synthetical allelopathic effect (SE) index of −0.36, whereas Rumex hastatus followed with an SE index of −0.38, indicating that S. arundinaceum was the least sensitive to A. adenophora stress. Our research findings elucidate the responses of indigenous grassland plants to A. adenophora, offering valuable insights into the screening of tolerant native grassland species and developing vegetation replacement strategies aimed at restoring invaded grasslands.