Effects of elevated CO2 and water stress on physiological responses of Perilla frutescens var. japonica HARA

The aim of the present study was to investigate the interactive effects of expected environmental constraints, specifically elevated CO2 and drought conditions, on the physiological responses of Perilla frutescens var. japonica Arum. Perilla frutescens var. japonica ‘Arum’ was exposed to 700 μmol mol−1 of CO2 under both well-watered and water-stressed conditions. Photosynthetic rate was higher under elevated CO2 conditions. Stomatal resistance increased while transpiration rates declined, which suggests that water-use efficiency rose under elevated CO2 conditions. Under water-stressed conditions, elevated CO2 concentrations induced much higher stomatal resistance than ambient CO2 levels. This result implies that elevated CO2 concentrations might increase plant sensitivity to water stress, thereby providing plants with increased protection against drought. Furthermore, elevated CO2 concentrations alleviated drought-induced photosynthetic decline in the early stages of drought, although this effect was not sustainable. Water stress also elevated ascorbate peroxidase (APX) activity but had little effect on glutathione reductase activity. Water stress-induced APX activity was much lower under elevated CO2 conditions compared to ambient CO2 levels. Therefore, elevated CO2 concentrations might increase plant resistance to water stress. Moreover, there is a possibility that increased ethylene evolution under elevated CO2 conditions could improve the capacity of plants to scavenge reactive oxygen species by enhancing APX activity.