In this study, the effect of environmental stress on the net photosynthesis was investigated under artificially controlled environment. In particular, effects of elevated ambient pressure on the CO2 exchange rate of aseptic medium-cultured plants, Arabidopsis thaliana, were discussed. In addition, the responsiveness of the net photosynthesis for temperature under elevated ambient pressure was investigated. Results showed the net photosynthesis increased under elevated ambient pressure regardless of the temperature. Besides, the responsiveness of the net photosynthesis to temperatures was changed under the elevated ambient pressures. These results suggest the usefulness of the elevated ambient pressure for plant growth.