Nanoparticles in nature are created by various natural biological and non-biological processes or human activities. Silver nanoparticles (Ag) are the most widely used nanoparticles in many medical, industrial, and consumer products. Therefore, Ag are expected to be widely distributed in the environment, affecting the living organisms. Also, the increasing entry of these nanoparticles into the soil may induce adverse effects on soil microbial activities and plants. This study was conducted in a completely randomized design with the aim of investigating the effects of Ag on soil microbial activity and some physiological traits of the maize plants. Silver nanoparticles, at nine levels of 0, 10, 50, 100, 250, 400, 600, 800, and 1000 µg/g soil, were added to pots containing maize plants with 4 replicates. Before harvesting the plants, fresh leaf samples were used to test the catalase enzyme activity. After 40 days of growth, the plants were harvested, oven-dried, and weighted. Silver concentration in the plant shoot and root were also measured. Soil samples were taken from the pots, air-dried, and stored at room temperature for measuring microbial respiration and mineralization rate of arginine. The results showed that the application of Ag decreased ( P 0.05) the arginine ammonification rate and microbial biomass carbon of the soil compared to those of the control. The addition of Ag had no significant effect on the soil basal respiration except for the 10 µg/g concentration, which slightly increased the basal respiration. The plants treated with 250 and 1000 µg/g of Ag showed significantly ( P 0.05) reduced shoot dry weight. Silver nanoparticles also significantly ( P 0.05) increased the activity of the catalase enzyme and the concentration of Ag in the shoots and roots of the plant. According to the results, Ag have some adverse effects on the soil microbial community and also cause oxidative stress in maize plants. Keywords : silver nanoparticles, corn plant, soil microbial activity, catalase enzyme.
