The effects of increasing salinity levels on Sulla carnosa photosynthesis are mainly of stomatal nature

Sulla carnosa Desf. plants were subjected to 0, 100, 200, and 300 mM NaCl for 40 days. Leaf and stem growth as well as root and leaf water contents were not affected even at 300 mM NaCl, confirming the halophytic nature of this species. An accumulation of Na+ in roots and at a higher magnitude in leaves together with a decline in K+ concentrations suggest that Na+ involvement in osmotic adjustment as a cheap osmoticum. This typical halophytic response together with the reduced transpiration rate by stomata closure may explain the ability of S. carnosa to maintain its water status. Interestingly, the stomatal limitations of photosynthetic activity did not affect Fv/Fm, F0, and PSII energy distribution to photochemical process [Y(II)], regulated non-photochemical quenching [Y(NPQ)], and non- regulated non-photochemical quenching [Y(NO)], which suggests a high ability of this halophyte to cope with the energy expected to exceed the demand for its photosynthesis.