Plant material, growth conditions and treatment conditions
Triticum aestivum L. ‘Chinese spring’,Oryza sativa L. ‘Japonica’, and Glycine max L. ‘William 82’ are model plants of wheat, rice and soybean, for their genomes have been published, respectively (Goff et al ., 2002; IWGSC, 2018; Schmutzet al ., 2010). The seeds were cultured in the plastic pots of 9 cm in diameter filled with mixture of vermiculite and peat soil. Thirty-day-old seedlings were transferred from culture room to open top chambers (OTCs, height 2.4 m, diameter 2.6 m). The open-top chambers (OTCs) were built and the gas dispensing system was conducted based on the previous method (Uprety, 1998). In this experiment, six chambers were used for two O3 levels, with three provided with elevated O3 (EO, 100 ppb) and the other three with charcoal filtered air served as the control (CF, <20 ppb). The injected O3 was produced by electrical discharge using ambient air by an O3 generator (CF-KG1, Shanmeishuimei Ltd., Beijing, China). During fumigation period, O3concentration was monitored above the plant canopy by ozone monitor (Model 106-L, 2B Tech. Inc., USA). According to the record of O3 monitor, O3 generator was regulated to maintain the objective concentration.