Impacts of Rhizobium inoculation and Fe3O4 nanoparticles on common beans plants: a magnetic study of absorption, translocation, and accumulation processes

We have carried out a systematic investigation on the impact of Fe₃O₄ nanoparticles (NPs) and Rhizobium inoculation on nodulation and growth of common bean plants (cv. Red Guama, Phaseolus vulgaris). Three distinct treatments were conducted on the common bean plants: (i) exposure to Fe₃O₄ NPs; (ii) Rhizobium inoculation; and (iii) a combined treatment involving Fe₃O₄ NPs + Rhizobium inoculation, with non-treated plants as controls. Temperature and magnetic field dependence of magnetization, M(T, H), measurements were performed on both the soil, and dried organs of the plants including roots, nodules, stems, and leaves. M(T, H) analyses indicated a systematic increase in magnetization across organs of plants treated with Fe₃O₄ NPs and combined Fe₃O₄ NPs + Rhizobium. We have found the magnetic contribution, generally related to Fe content in the soil and plant organs, significantly increased in plants exposed to Fe₃O₄ NPs, further indicating absorption, translocation, and accumulation of Fe₃O₄ NPs in the areal parts of the plants. Plants treated with Fe₃O₄ NPs and combined Fe₃O₄ NPs + Rhizobium exhibited Fe₃O₄ NPs accumulation in all organs with increasing concentrations of 69.7 to 74.1 N_NPs/g in roots, 5.6 to 7.7 N_NPs/g in stems, and 3.1 to 5.5 N_NPs/g in leaves, respectively. The iron concentration in nodules was found to be close to 65 N_NPs/g. No appreciable difference in the absorption index AI of roots between plants treated with Fe₃O₄ NPs (~ 1.73%) and Fe₃O₄ NPs + Rhizobium (~ 1.79%) has been observed. The translocation index TI increased by ~ 46% in plants treated with Fe₃O₄ NPs + Rhizobium (6.9%) compared to Fe₃O₄ NPs (4.3%). Treated plants showed improved symbiotic performance including nodule leghaemoglobin and iron content, number of active nodules per plant, and nodule dry weight. The best result was obtained using the combined treatment of Fe₃O₄ NPs + Rhizobium. This study provides evidence that M(T,H) measurements constitute a valuable tool in monitoring the uptake, translocation, and accumulation of Fe₃O₄ NPs in plant organs of common bean plants.