Damask rose waste-derived biochar enhances polyethylene microplastic tolerance in Borago officinalis L. by strengthening antioxidant defense and preserving photosynthetic performance

Introduction The widespread presence of microplastics in agricultural soils is increasingly recognized as a major environmental constraint affecting plant performance and crop productivity. In the present work, we explored whether biochar produced from distillery residues of Damask rose ( Rosa damascena ) could lessen the harmful effects of polyethylene microplastics (PE-MPs) on European borage ( Borago officinalis L.). Methodology The experiment was carried out in two sequential stages. An initial screening trial compared five DRW-B application rates (0, 0.75, 1.25, 2.5, and 5% w/w). The 2.5% rate had the highest mean for four of the five growth traits and was selected as the most promising tested rate for the subsequent PE-MP experiment. In the second stage, the selected biochar rate was tested in combination with five PE-MPs concentrations (0, 10, 50, 100, and 500 mg kg −1 ). Results Exposure to PE-MPs caused pronounced reductions in plant growth and physiological performance. Compared with the control, root length, dry biomass, leaf area, total chlorophyll, and carotenoid content declined by 80%, 74.4%, 70.6%, 69.9%, and 72.8%, respectively. At the same time, indicators of cellular damage increased markedly, as reflected by a 3.7-fold rise in malondialdehyde concentration and a fivefold increase in electrolyte leakage. Incorporation of biochar at 2.5% (w/w), however, substantially moderated these negative responses. Plants grown in biochar-amended soil showed stronger antioxidant activity, including higher ascorbate peroxidase, guaiacol peroxidase, and phenylalanine ammonia-lyase activities, together with greater anthocyanin accumulation. The enhancement of these protective mechanisms helped limit oxidative injury, maintain photosynthetic function, and preserve pigment concentrations under microplastic stress. DRW-B substantially moderated these adverse responses; At the highest PE-MP concentration, DRW-B increased dry biomass by 106.1% and Fv/Fm by 65.4%, while reducing MDA and electrolyte leakage by 14.7% and 13.5%, respectively, compared with the corresponding treatment without biochar. Conclusion The research indicates that biochar derived from Damask rose processing waste can serve as an effective amendment for reducing PE-MP-induced stress in B. officinalis . By strengthening multiple antioxidant defense pathways, this sustainable by-product offers a practical option for supporting the cultivation of medicinal plants in soils affected by microplastic contamination.