Concentration-Dependent Effects of Artemisia annua Aqueous Extract on Seed Germination, Seedling Growth, and Physiological Responses of Solanum rostratum

This study examined the concentration-dependent effects of an aqueous extract of Artemisia annua on seed germination and seedling morphological and physiological traits in the invasive plant Solanum rostratum. The extract was also subjected to preliminary chemical profiling using LC–MS/MS. Seed germination was examined in Petri dishes at 50, 100, 150, 200, and 250 g L−1, whereas seedling responses were examined in independent plug cells at 100, 150, 200, 250, and 300 g L−1. Distilled water served as the control in both experiments. Widely targeted LC–MS/MS profiling of the 300 g L−1 extract yielded 9987 putative metabolite annotation entries across ten superclasses, with phenylpropanoids, alkaloids, and terpenoids, constituting the three largest superclasses by number of annotation entries. Seed germination was suppressed at all tested concentrations and completely inhibited at ≥150 g L−1. Seedling responses were concentration-dependent: several morphological indices increased at 100–150 g L−1 while gas-exchange performance declined, whereas morphological inhibition became increasingly evident at ≥200 g L−1. Net photosynthetic rate, stomatal conductance, and transpiration rate declined with increasing extract concentration and were significantly lower under all extract treatments than in the control. Chlorophyll a and chlorophyll b contents initially increased and then decreased, with both peaking at 150 g L−1. Carotenoid content increased across the concentration gradient, whereas intercellular CO2 concentration exceeded the control only at ≥200 g L−1. Electrolyte leakage and the contents of malondialdehyde, H2O2, and proline generally increased with extract concentration, with the highest values observed at 300 g L−1. Catalase activity was significantly lower than that of the control at ≥200 g L−1. At high concentrations, morphological inhibition coincided with reduced photosynthetic performance, changes in antioxidant enzyme activities, and increased indicators of oxidative stress and membrane damage. These findings provide laboratory evidence of the phytotoxic potential of A. annua aqueous extract but do not establish its efficacy or safety under field conditions.