Nickel boots antioxidant defense and nutrient uptake, reducing deleterious effects on biomass in soybean plants copper-stressed

Copper (Cu) accumulation in soils often results from industrial activities, illegal mining, and Cu-based fungicide use, inhibiting chlorophyll biosynthesis, impairing photosynthesis, causing oxidative stress, and suppressing the defense system. On the other hand, nickel (Ni) is an element relevant in leguminous plants and essential to nitrogen metabolism. Therefore, this research evaluated the effects of Ni supplies on Cu-stressed soybean plants, analyzing the nutrient contents, chlorophyll pigments, gas exchange, antioxidant enzymes, and stress indicators. The research was conducted in a completely randomized design with a factorial 2x3, with two Cu levels, defined as Cu control Cu (100 mg kg−1) and Cu excess (500 mg kg−1), and three Ni levels (0.2, 1.0, and 3.0 mg kg−1). Results revealed that Ni supplies improved the nutritional status in plants under Cu excess, with better responses with 3 mg kg−1 Ni. Plants treated with Ni and exposed to Cu stress had boosted the antioxidant system, increasing catalase (21 to 37%) and ascorbate peroxidase (43 to 66%). when compared to the same treatment with lower Ni supply and Cu excess (0.2 mg kg−1 Ni + 500 mg kg−1 Cu). Ni treatment mitigated the negative impacts induced by Cu stress on photosynthetic pigments, photosynthesis, and biomass. Therefore, our results validate the benefits related to Ni application in soybean plants Cu-stressed.