Effect of γFe2O3 nanoparticles on photosynthetic characteristic of soybean (Glycine max (L.) Merr.): foliar spray versus soil amendment

There is an urgent need to address comprehensive biosafety issues associated with the use of Fe2O3 nanoparticles (IONPs). The present study was performed to investigate the effect of 6-nm IONPs and citrate-coated IONPs (IONPs-Cit) on photosynthetic characteristics and root elongation during germination of Glycine max (L) Merr. Plant physiological performance was assessed after foliar and soil IONPs fertilization. No adverse impacts at any growth stage of the soybeans were observed after application of IONPs. The Fe2O3 nanoparticles produced a significant positive effect on root elongation, particularly when compared to the bulk counterpart (IOBKs) suspensions of concentrations greater than 500 mg L−1. Furthermore, IONPs-Cit significantly enhanced photosynthetic parameters when sprayed foliarly at the eight-trifoliate leaf stage (P < 0.05). The increases in photosynthetic rates following spraying were attributed to increases in stomatal opening rather than increased CO2 uptake activity at the chloroplast level. We observed more pronounced positive effects of IONPs via foliar application than by soil treatment. This study concluded that IONPs coated with citric acid at IONPs to citrate molar ratio of 1:3 can markedly improve the effectiveness of insoluble iron oxide for Fe foliar fertilization.