Beneficial or detrimental? How nickel application alters the ionome of soybean plants

The use of nickel (Ni) in agriculture may represent one of the most significant cases of plant hormesis ever reported, as plants exhibit both positive and negative responses depending on the level of exposure to this element. For a more comprehensive understanding of this effect, the next step is to conduct studies on the dynamics of preexisting chemical elements in the system (ionomic profile), especially when introducing Ni as a novel nutrient for the plants. This micronutrient is of particular interest to the fertilization of leguminous plants, such as the soybean, due to its additional effects on the biological nitrogen fixation process. This study thus evaluated the influence of five doses of Ni (0.0, 0.5, 1.0, 3.0, and 9.0 mg of Ni kg(-1)) on the ionomic profile of soybean genotypes using modern quantification techniques. The results revealed that the addition of Ni reduced the concentration of cationic micronutrients manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu), while it increased the concentration of macronutrients nitrogen (N) and magnesium (Mg). The application of Ni also resulted in a reduction of the potentially toxic element aluminum (Al). Correlations were also observed for these elements, indicating that Ni could be a controlling agent in elemental absorption and translocation. The ionome of the leaf tissues exhibited the most significant alterations, followed by the grains, nodules, and roots. Exogenous agronomic doses of Ni proved beneficial for the growth and production of soybean plants, although a genotypic effect was observed. The treatment with 9.0 mg of Ni kg(-1), resulted in a new ionomic profile related to toxicity, demonstrating suboptimal plant development. Thus, the application of Ni in appropriate doses had a significant impact on the ionomic profile of soybeans, improving plant development and implying resistance to potentially toxic elements such as Al.