It has been recognized widely that sequestration of atmospheric CO2 by terrestrial ecosystems can contribute significantly to the stabilization of atmospheric CO2. The carbon sequestration potential of crop lands should be considered as a modest but non-negligible contribution to climate change mitigation. Salinity is one of the most important environmental factors limiting crop production of marginal agricultural soils in many parts of the world. In our research, several physiological analyses were performed in atmospheric CO2, in daylight, both in normal conditions and with salinity (40 mm NaCl). Crops like melon or pepper showed significantly lower photosynthetic rates when they were grown in saline conditions. Also, the total chlorophyll content and carbon percentage were lower in the salinity-treated plants of these species. For lettuce, treated plants showed a significant decrease in photosynthetic rates and chlorophyll content, but there were no differences in carbon content. On the other hand, there were no significant differences in the values of total chlorophyll content, photosynthetic rate, or carbon content for tomato and watermelon plants when control and NaCl-treated plants were compared. The mineral composition data showed greater increases of sodium in both roots and leaves of melon and pepper when plants were treated with NaCl compared with the rest of the species. In conclusion, tomato and watermelon seem to be more efficient in CO2 fixation than the other crops of this experiment and this seems to be related to their greater salinity tolerance.