A multi-nutrient nanocomposite enhances UV stress tolerance and modulates nutrient accumulation in lettuce

This study introduces a novel multielement (Zn-Mg-Mn-Fe) nanocomposite that serves both as a UV-protective agent and a nutrient delivery system for Lactuca sativa (lettuce). Plants were grown indoors in a potting soil-like mix, under artificial lighting (from light emitting diodes, LEDs) or under LED+UV radiation to simulate excessive sunlight exposure (light stress). Lettuce was treated with foliar applications of the nanocomposite at 100 mg/L, 200 mg/L, and 300 mg/L, with 1 mL applied per plant during the fifth week of growth (a total of 0.1, 0.2 or 0.3 mg of the composite respectively per plant). Plants were exposed to UV radiation (360–400 nm) for 10 hours daily over two weeks. The 300 mg/L treatment significantly enhanced photosynthetic efficiency and plant growth, increasing chlorophyll content (66.7% ± 3.5), leaf area (45% ± 2.1), and dry biomass (43.68% ± 1.8) compared to untreated and ionic controls. It also mitigated UV-induced stress, reducing UV-induced damage scores by 73% compared to controls and lowering stress markers, with flavonoid production reduced to 30.5% ± 2.3 of control levels and SOD activity reduced to 25.8% ± 1.8 of control levels. The composite’s-controlled nutrient release mechanism facilitated rapid Mg uptake (220 mg/kg dry weight in leaves within 4 days) and sustained delivery of Zn, Mn, and Fe over a 7–10-day period. Long-term nutrient uptake analysis showed increases in Mn (55.3% ± 3.2), Mg (47.8% ± 2.7), and Fe (62.5% ± 4.1). Enhanced P (28.5% ± 2.2) and K (35.7% ± 3.1) accumulation further boosted the nutritional quality of edible tissues. Additionally, the nanocomposite demonstrated the unique ability to convert harmful UV radiation into visible light, providing dual benefits of UV protection and enhanced photosynthetic activity. These findings highlight the potential of this multi-functional nanocomposite as a sustainable solution to improve crop resilience, optimize nutrient delivery, and combat environmental stress in agricultural systems.