Comparative toxicological effects of traditional and biodegradable microplastics on pepper (Capsicum annuum L.): physiological and metabolomic insights

Microplastics (MPs), as emerging environmental contaminants, increasingly threaten plant performance in agricultural ecosystems, yet the differential toxicity of traditional and biodegradable MPs remains unclear. Here, we conducted a 60-day soil culture experiment to evaluate the effects of six MPs, four traditional polymers and two biodegradable plastics, on pepper (Capsicum annuum L.) at 0.1 % and 0.5 % (w/w). Growth inhibition occurred in a type- and dose-dependent manner, with non-degradable PP-MPs and PS-MPs exerting stronger effects than biodegradable MPs. PBS-MPs caused the most severe oxidative stress, increasing HO content by 205.4 %. Metabolomic analyses revealed metabolic reprogramming under MPs exposure, with flux shifting from photosynthetic carbon assimilation/glycolysis to the pentose phosphate pathway. Notably, PVC-MPs imposed stronger inhibition on carbon assimilation/glycolysis. Metabolomic analysis further revealed that oxidative stress was closely associated with metabolic reprogramming: biodegradable MPs (PLA, PBS) markedly disrupted aromatic amino acid biosynthesis (e.g., tyramine decreased by 73.8 %), thereby weakening the basis for antioxidant defense, whereas traditional PS-MPs specifically suppressed downstream phenylpropanoid metabolism (e.g., 4-hydroxycinnamic acid and sinapic acid decreased). Collectively, these findings demonstrate that biodegradable and traditional MPs induce phytotoxicity through distinct mechanisms: biodegradable MPs primarily trigger oxidative damage and perturb primary metabolism, whereas traditional MPs preferentially suppress energy metabolism and secondary defense pathways. This study provides mechanistic insights into MPs-induced stress responses in pepper and highlights potential risks of both traditional and biodegradable MPs to agroecosystem health.