Figure legends
Fig.1 Effects of elevated [O3] on CO2 assimilation rate (A sat) (A), stomatal conductance (gs) (B), ratio of CO2 concentration in intercellular and ambient (Ci/Ca) (C) and transpiration rate (E) (D) of wheat, rice and soybean. Columns in the figure represent means ± SE (n =6) and two asterisks (**) on bars indicate significant differences between charcoal filtered air (CF) and elevated [O3] (EO) treatment for each crop at the 0.01 level.
Fig. 2 Effects of elevated [O3] on activities of superoxide dismutase (SOD) (A), peroxidase (POD) (B), and catalase (CAT) (C) and hydrogen peroxide (H2O2) (D) in wheat, rice and soybean leaves. Columns in the figure represent means ± SE (n =3). One asterisk (*) and two asterisks (**) on bars indicate significant differences at the 0.05 and 0.01 level between charcoal filtered air (CF) and elevated [O3] (EO) treatment for each crop, respectively.
Fig. 3 Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) for the three crops. A: PCA analysis between sample groups. B-D: PLS-DA score plots of the metabolite profiles of different crops in treatment and control groups. B: Tae, wheat; C: Osa, rice; D: Gma, soybean.
Fig. 4 Differential metabolites. (A) The common or specific different metabolites in three species under elevated O3. (B-D) Classification of differential metabolites under O3 stress according to chemical groups identified in three species wheat (B), rice (C) and soybean (D).
Fig.5 KEGG enrichment analysis of differential metabolites in wheat, rice, and soybean (P <0.05). Tae, wheat; Osa, rice; Gma, soybean.
Fig. 6 Overview of metabolite changes in wheat exposed to O3. A schematic view of different metabolic pathways in which metabolites were affected by O3 is shown. The increased metabolites are marked in red and the decreased onesare marked in blue . Abbreviations: G6P, glucose-6-phosphate; F6P, fructose-6-phosphate; 3PGA, 3-phosphoglycerate; PEP, phosphoenolpyruvate; HMP, hexose monophosphate pathway; MEP, methylerythritol 4-phosphate; MVA, mevalonic acid; TCA, tricarboxylic acid cycle; IPP, isopentene pyrophosphate; DMAPP, dimethylallyl pyrophosphate; GPP, geranylpyrophosphate; FPP, farnese pyrophosphate; GGPP, geranylgeranyl pyrophosphate.
Fig. 7 Overview of metabolite changes in rice exposed to O3. A schematic view of different metabolic pathways in which metabolites were affected by O3 is shown. The increased metabolites are marked in red and the decreased ones are marked in blue. Abbreviations: G6P, glucose-6-phosphate; F6P, fructose-6-phosphate; 3PGA, 3-phosphoglycerate; PEP, phosphoenolpyruvate; HMP, hexose monophosphate pathway; MEP, methylerythritol 4-phosphate; MVA, mevalonic acid; TCA, tricarboxylic acid cycle; IPP, isopentene pyrophosphate; DMAPP, dimethylallyl pyrophosphate; GPP, geranylpyrophosphate; FPP, farnese pyrophosphate; GGPP, geranylgeranyl pyrophosphate.
Fig. 8 Overview of metabolite changes in soybean exposed to O3. A schematic view of different metabolic pathways in which metabolites were affected by O3 is shown. The increased metabolites are marked in red and the decreased ones are marked in blue. Abbreviations: G6P, glucose-6-phosphate; F6P, fructose-6-phosphate; 3PGA, 3-phosphoglycerate; PEP, phosphoenolpyruvate; HMP, hexose monophosphate pathway; MEP, methylerythritol 4-phosphate; MVA, mevalonic acid; TCA, tricarboxylic acid cycle; IPP,  isopentene pyrophosphate; DMAPP, dimethylallyl pyrophosphate; GPP, geranylpyrophosphate; FPP, farnese pyrophosphate; GGPP, geranylgeranyl pyrophosphate.
Fig. 9 The expression level of genes coding key enzymes. Columns in the figure represent relative expression ± SE of three biological samples. A: Rhe gene coding citrate (Si)-synthase (EC2.3.3.1); B: The gene coding ATP citrate synthase (EC2.3.3.8); C: The gene coding isocitrate dehydrogenase (EC1.1.1.41); D: The gene coding oxoglutarate dehydrogenase (EC1.2.4.2); E: The gene coding aspartate transaminase (EC2.6.1.1).