2.1. Experimental Conditions

Faisalabad, the Manchester of Pakistan, is a famous industrial hub and is well-known for the food and textile industry. At 184 m above sea level, it is situated between longitude 73°E and latitude 31.15°N. The present study was conducted to evaluate the impact of ascorbic and silicic acid foliar application on mung bean under an elevated O₃ level. Twelve mung bean varieties, NM-28, 13-1, 19-19, 20-21, 121-25, 51, 54, 92, 98, 2006, 2011, and NM 2016, were investigated in the present study, and seeds were collected from NIAB, Faisalabad. Plants were grown in pots under controlled conditions of glass house (average temperature, i.e., 30 °C, and relative humidity, i.e., 49%) with four sets and three replications. Seeds were sterilized with 0.2% HgCl₂ before sowing. Three weeks after germination, 10 mM ascorbic acid and 0.1 mM silicic acid (selected from pretrial experiment) were applied as foliar spray with 0.1% Tween-20 as a surfactant (Figure ​Figure11).

Experimental setup for the current study showing the experiment site (A), ambient O₃ level (B), elevated O₃ level (C), elevated O₃ and ascorbic acid (D), and elevated O₃ and silicic acid (E).

The soil was analyzed for initial physiochemical characteristics using a homogenized soil sample (pH 7.71), and the analytical results are shown in Table 1. A hydrometer was used to determine the soil texture.⁴⁹ For the basic soil organic matter calculation, the Walkley–Black methodology was used.⁵⁰ The complete and bioavailable concentrations of selected metals lead (Pb), zinc (Zn), cadmium (Cd), and iron (Fe) were assessed by digesting the soil in a particular ratio of HNO₃ and HClO₃⁵¹ in addition to employing ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) to extract the samples.⁵²

The O₃ gas was produced with the help of an O₃ generator (AOT-MD-500 model). Pure oxygen was used as a source of gas. This O₃ generator is an electrical device that feeds oxygen gas and converts this oxygen into O₃ gas. A system was set up for O₃ exposure in a glass house consisting of (1) an O₃ generator, (2) a UV photometry O₃ analyzer (model: 0342e), (3) an oxygen cylinder, and (4) an oxygen delivery pipe that links the O₃ generator with the oxygen cylinder. Plants were fumigated with an elevated O₃ level of 120 ppb except for the control. Continuous 4 h of O₃ monitoring was done with an O₃ analyzer (model: 0342e). The elevated O₃ level was maintained for 15 days. Normal air was considered a control treatment.