Foliar Application of Iron Nanoparticles Improves Chinese Cabbage Growth

Iron deficiency limits plant growth and is usually addressed with iron fertilizers. Iron-based nanomaterials (nZVI, α-FeOOH, α-Fe₂O₃, γ-Fe₂O₃, and Fe₃O₄) show promise as novel alternatives, but the effects of sulfide nano-zero-valent iron (S-nZVI) on crops remain little studied. Thus, this study aimed to synthesize a novel iron-based nanomaterial, S-nZVI, using a one-step method, and to evaluate the effects of S-nZVI and nZVI at concentrations ranging from 5 to 100 mg L^-1 on the physiological and photosynthetic characteristics of Chinese cabbage (Brassica rapa L.). In the study, foliar application of iron nanoparticles increased leaf area, biomass, and photosynthesis, with 50 mg L^-1 the most efficient concentration (S-nZVI > nZVI). Moreover, the photosynthetic rate of the leaves increased significantly (>200%), and carbohydrate accumulation also increased significantly. Additionally, S-nZVI treatment increased leaf iron content by 5.8-fold compared to the control group, likely by enhancing the activity of antioxidant enzymes. However, the 100 mg L^-1 S-nZVI treatment significantly inhibited these physiological and biochemical indicators. Overall, the foliar S-nZVI (50 mg L^-1) enhanced Chinese cabbage growth by alleviating iron deficiency, boosting antioxidant activity, and reducing oxidative stress; further field trials are needed to verify its effectiveness and cost-efficiency.