The photosynthetic pathway of Crassulacean acid metabolism (CAM) is important for plants in stressful environments. Portulaca is one of the few genera that exhibit C 4-CAM photosynthetic transition under drought, but its timeline and ecophysiological changes during C 4-CAM transition under salinity are still lacking. Here, we monitored CAM activity in the leaves of P. grandiflora (strong CAM) and P. molokiniensis (weak CAM) under salinity and drought conditions and investigated their recovery after stress. According to the day/night fluctuation of traits related to CAM activity, CAM photosynthesis was initiated in P. grandiflora under high salinity and severe drought on day 6 and under medium salinity and moderate drought stress on day 8. Additionally, CAM photosynthesis was initiated in P. molokiniensis under high salinity on day 12 and under severe drought on day 10, and medium salinity and moderate drought on day 16. After stress, these plants decreased CO 2 uptake, Rubisco activity, chlorophyll fluorescence and soluble protein. We also found day/night changes in proline and malondialdehyde in P. grandiflora under both stresses, while P. molokiniensis remained unaffected. Root length, root volume and root surface area of P. grandiflora responded only under severe drought during C 4-CAM transition, while P. molokiniensis responded under high salinity and severe drought. During recovery, P. grandiflora completely switched from CAM to C 4 within a week, but only after one week in P. molokiniensis under moderate and severe drought and within two weeks in P. grandiflora, but only after two weeks in P. molokiniensis under high salinity. The results defined the transition and recovery phases of Portulaca based on their ecophysiological traits, which revealed the mechanisms underlying the adaptation during the C 4-CAM transition and to predict responses of C 4 plants to increasing drought and salinity under future climate change.