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In this investigation, the effect of salt stress on <i>Portulaca oleracea</i> L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in CO₂ assimilation (A) at the beginning of salt exposure (day 3). However, the leaf water potential (ψ_w), the substomatal concentration of CO₂ (Ci), the maximum quantum yield of photosystem II (Fv/Fm), and the proline and malondialdehyde (MDA) content remained unchanged. Exposure to 300 mM NaCl caused a decrease in gs from day 3 and a decrease in water potential, CO₂ assimilation, and Fv/Fm from day 9. There was a large increase in proline content and a significantly higher MDA concentration on days 6 and 9 of salt stress compared to the control group. After 22 days of exposure to 300 mM NaCl, there was a transition from the C4 cycle to crassulacean acid metabolism (CAM), manifested by a rapid increase in substomatal CO₂ concentration and negative CO₂ assimilation values. These results document the tolerance of <i>P. oleracea</i> to a lower level of salt stress and the possibility of its use in saline localities.