Influence of Nickel on Urease Activity and Nitrogen Dynamics in Maize (Zea mays) Under Saline Conditions

Nickel (Ni) is a vital micronutrient that significantly contributes to essential plant functions, including normal growth, enzymatic activities, and nitrogen metabolism. Soil urease activity can markedly decrease under saline conditions, and both plants and soil organisms necessitate Ni for the effective assimilation of urea. This study investigates the effects of varying levels of Ni supplementation (0, 25, 50, and 100 mg kg-1) under saline soil conditions on soil and plant urease activity, biomass yield, chlorophyll content, nitrogen (N) content, and nitrate assimilation. Thermal imaging was employed to assess plant stress by measuring leaf temperature. Results showed that the 25 mg kg-1 Ni treatment notably improved soil urease activity, leading to enhanced nitrogen uptake and biomass production. This Ni dose also resulted in the lowest leaf temperature in maize, indicating reduced stress. Low Ni levels increased nitrate reductase (NR) activity, nitrate content, and free amino acids in maize, while sharply reducing ammonium accumulation, suggesting that Ni promotes plant growth by regulating nitrogen assimilation. However, the 100 mg kg-1 dose caused toxicity in maize. All Ni concentrations decreased plant urease activity, indicating decreased urea uptake from the soil. Overall, these findings suggest that low doses of Ni support nitrogen metabolism and plant performance by regulating urease activity in both soil and plants, while higher doses have toxic effects.