Metallic nanoparticles and magnetic pellets synergistically optimize growth, antioxidant defense, and visual quality of Portulaca oleracea L. in urban vertical green walls

Background Establishing medicinal and groundcover species like Portulaca oleracea L. in urban green walls requires innovative approaches to overcome restrictive environmental conditions. This study evaluated the morphophysiological, biochemical, and antioxidant responses of purslane grown in an outdoor green wall to the individual and interactive effects of metallic nanoparticles (silver: N1; titanium dioxide: N2; and combined: N3) and Magnet Pellet treatments (Level 1: M1; Level 2: M2; and control: M3). Results The interaction between nanoparticles and Magnet Pellet significantly influenced most of the evaluated plant traits. Combined applications markedly enhanced canopy coverage, survival duration, and visual quality compared with the control. Under the significant NPs × Magnet Pellet interaction, the N1M1 treatment combination yielded the highest growth index (25,000 cm 3 ), representing a 595% increase over the lowest-performing combination (N3M3: 3,598 cm 3 ). The maximum root surface area (99.27 cm 2 ) and root dry weight (1.96 g) were recorded under the N3M1 treatment. While the application of silver nanoparticles alone (N1M3) caused the highest proline accumulation (1.60 mg g⁻ 1 fresh weight) indicating an emergency adaptive response to nanoparticle-induced stress—the addition of M1 (N1M1) significantly reduced proline concentration to 1.40 mg g⁻ 1 fresh weight, redirecting metabolic energy toward vegetative growth. The N2M1 treatment produced the most balanced vegetative performance, achieving the highest total chlorophyll content (9.73 μg mg⁻ 1 ), maximum total biomass (22.96 g), and highest total soluble proteins, while minimizing lipid peroxidation (malondialdehyde: 0.17 μmol g⁻ 1 fresh weight). Furthermore, Magnet Pellet application improved relative water content, reduced electrolyte leakage, and optimized the activities of superoxide dismutase and guaiacol peroxidase. Maximum phenolic accumulation (5.08 mg g⁻ 1 fresh weight) occurred in N2M3. Conclusions In green wall engineering, high biomass production, prolonged leaf greenness, and delayed cellular senescence are crucial characteristics. The synergistic application of titanium dioxide nanoparticles and Magnet Pellet Level 1 (N2M1) effectively mitigates stress and boosts overall physiological performance. This combination is recommended as a highly effective and innovative nutritional strategy to ensure long-term aesthetic quality, plant health, and durability in urban vertical green infrastructures.