Does CO₂ ameliorate phytotoxic effects of O₃? A study case on their interactive effects on physiology, and yield of potato (Solanum tuberosumL. Cv. Kara) plants

Potato (Solanum tuberosum L. cv. Kara) was grown in Open‐Top Chambers (OTCs) in Northern Egypt at ambient (ca 350 ppm) or doubled CO₂ (ca 690 ppm) either in charcoal‐filtered air (15 nl l‐1) or in non‐filtered ambient air (78 nll‐1 O₃) to investigate the changes in physiology and yield under long‐term elevated CO₂ and/or O₃ throughout 100 days. Ambient O₃ level reduced net photosynthetic rates, number and weight of tubers by 18 per cent, 41 per cent and 21 per cent, respectively, whereas elevated CO₂ caused the opposite effect where it increased the same parameters by 44 per cent, 37 per cent and 20 per cent, respectively. Significant O₃ x CO₂ interactions were detected. However, O₃ caused an increase in GR and POD by 18 per cent and 35 per cent, respectively, while CO₂ caused an increase in POD only by 46 per cent, and there was no effect of O₃ and/or CO₂ on other enzymes. The results of this study are discussed in relation to predicted atmospheric changes.