Superior effects of root-applied Fe 2 O 3 nanoparticles synthesized from safflower seeds on growth and photosynthesis in safflower

Iron (Fe) is vital for plant growth and metabolism, and green synthesis provides an eco-friendly approach to produce nanoparticles (NPs) using plant extracts. In this study, iron oxide NPs (Fe2O3NPs) were greenly synthesized from safflower (Carthamus tinctorius) seed extract and characterized for their structural, optical, and biological properties. UV–Vis analysis revealed a peak at 351.8 nm, while FTIR confirmed Fe-O bonding and surface functionalization by phytochemicals. The NPs exhibited an average size of 281.4 nm, a zeta potential of −19.9 mV, and predominantly spherical morphology. Antifungal assays demonstrated strong inhibitory activity against Fusarium oxysporum (20.83 ± 0.09 mm) and Alternaria solani (20.33 ± 1.00 mm). Subsequently, Fe2O3NPs were applied to safflower at increasing concentrations via foliar spraying and root nutrient solution, and chlorophyll fluorescence was measured every two days over 7 days. Foliar applications of 60 mg/L and higher negatively affected PSII activity from day one, restricting electron flow toward PSI, with the effect intensifying over time. Conversely, high root-applied concentrations (100–400 mg/L) markedly reduced photosynthetic efficiency, whereas 60 mg/L root application enhanced photosynthetic performance from the first day. On day 7, growth and Fe accumulation in shoots and roots indicated that foliar application more strongly enhanced growth and photosynthetic activity, while low root-applied concentrations promoted development. Overall, these findings highlight the critical roles of both NP concentration and application method in regulating the physiological and photosynthetic responses of safflower, providing insights for the sustainable use of Fe2O3NPs in crop management.