Abstract: Few studies have explored plant responses to all of CO₂ scenarios including 430-480, 580-720, 720-1000 and more than 1000 μmol·mol^-1 which will be by 2100 predicted by the IPCC (Intergovernmental Panel on Climate Change). In this study, one-year-old seedlings of Schima superba were exposed to ambient air and three elevated CO₂ concentrations of 550, 750, 1000 μmol·mol^-1 to investigate the changes of gas exchange parameters, photosynthetic pigment contents, and biomass by using Open Top Chambers during growing season. The results showed that net photosynthetic rate was increased by 32.7%, 66.7%, and 82.7%, and intercellular CO₂ concentration was increased by 60.3%, 126.2%, 223.9% at 550, 750, and 1000 μmol·mol^-1, respectively. The improvement in net photosynthetic rate under elevated CO₂ concentrations decreased as affected by non-stomatal factors (such as decreased leaf N content) after longer fumigation time. Stomatal conductance and transpiration rate increased under all elevated CO₂ concentrations from May to July, while there was no significant difference between 1000 μmol·mol^-1 and ambient treatments from August to October. The reduction of the contents of chlorophyll a, chlorophyll b, carotenoids, and N in leaves under 750 and 1000 μmol·mol^-1 was higher than that under 550 μmol·mol^-1. Biomass under the treatments of 550 and 750 μmol·mol^-1 increased by 79.2% and 48.9%, respectively, but decreased under 1000 μmol·mol^-1. Therefore, it would be beneficial for S. superbato fix the increasing CO₂ in atmosphere and preserve water in body under elevated CO₂ concentrations. These benefits would increase the adaptability of S. superba seedlings to arid environments and enhance biomass accumulation under CO₂ concentrations of 550 and 750 μmol·mol^-1.

Key words: CO₂ enrichment, OTC, gas exchange parameter, photosynthetic pigment, biomass.