Nickel (Ni) is an essential metallic micronutrient for optimal plant growth and development, regulator of essential metabolic processes, but its interaction with other essential nutrients can result in differences in the absorption of these nutrients, which can disrupt the ionic balance. The objective of this research was to evaluate the physiological performance and growth of soybean plants subjected to Ni levels applied via soil under Fe (iron) excess, determining the behavior of redox metabolism, gas exchange, and photosynthetic pigments. The experiment was conducted in a completely randomized design with a factorial 2 × 3, with two Fe levels, defined as control Fe (35.7 μM) and excess Fe (357 μM), and three Ni levels (0.2, 1.0, and 3.0 mg kg−1). Results revealed that Fe toxicity caused significant reductions for leaf dry matter (LDM) and stem dry matter (SDM), but Ni applied to the soil provided increases of 8% and 22% in LDM and SDM. Treatment with toxic Fe caused reductions in photosynthetic pigments in soybean plants. However, 3.0 mg kg−1 Ni caused increases (p < 0.05) of 10%, 12%, 10%, and 36% for chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids. Plants treated with 3.0 mg kg−1 Ni and exposed to Fe stress had boosted the antioxidant system, increasing catalase (14%) and ascorbate peroxidase (16%), while the oxidative damage occasioned by Fe excess in was reduced 6% and 3% in malondialdehyde and hydrogen peroxide, as compared to Fe excess +0.2 mg kg−1 Ni. Therefore, the Ni application via soil under experimental conditions was found to be a possible mitigator of the phytotoxic effects caused by Fe excess in soybean plants.
Pereira et al. (2026) studied this question.