<p>Values are mean±SD, error bars represent standard deviation (sample size, n = 12 for I and II, n = 16 for III, IV and V). Lower letters represent significant difference at p<0.05 among TiO<sub>2</sub> NPs treatments under the same CO<sub>2</sub> conditions; Upper letters represent significant difference at p<0.05 between super-elevated CO<sub>2</sub> and normal CO<sub>2</sub> conditions at the same TiO<sub>2</sub> NPs concentration.</p