Higher Ps rate under ECO2 + AO3 and ECO2 + EO3 compared to
ACO2 + AO3 was recorded during the present study. Increments inPs rate of potato (cv. Bintje) up to 40% in response to 720 ppm CO2
(Katny et al., 2005) and 53% in cv. Shepody under ambient + 350
ppm CO2 (Conn and Cochran, 2006) were reported. An increase in
Ci under ECO2 + AO3 and ECO2 + EO3 compared to ACO2 + AO3 may
have reduced RuBP oxygenation and at the same time may have
enhanced RuBP carboxylation, resulting in an increase in Ps rate
(Rao et al., 1995). Morison (1998) suggested that Ci could be the