OUP accepted manuscript

NaCl stress affects stomatal behavior and photosynthesis, by a combination of osmotic and ionic components, but it is unknown how these components affect stomatal and photosynthetic dynamics. Tomato (Solanum lycopersicum) plants were grown using a reference nutrient solution (Control, EC: 2.3 dS m -1), a solution containing additional macronutrients (osmotic effect; EC: 12.6 dS m -1), or a solution with additional 100 mM NaCl (osmotic and ionic effects; EC: 12.8 dS m -1). Steady-state and dynamic photosynthesis along with leaf biochemistry were characterized throughout leaf development. The osmotic effect decreased steady-state stomatal conductance, while speeding up stomatal responses to light intensity shifts. After 19 days of treatment, photosynthetic induction was reduced by the osmotic effect, which was attributable to lower initial stomatal conductance due to faster stomatal closing rate under low light. Ionic effects of NaCl were barely observed in dynamic stomatal and photosynthetic behavior, but led to a reduction in leaf photosynthetic capacity, CO2 carboxylation rate and stomatal conductance in old leaves after 26 days of treatment. With increasing leaf age, rates of light-triggered stomatal movement and photosynthetic induction decreased across treatments. We conclude that NaCl impacts dynamic stomatal and photosynthetic kinetics by osmotic effects and reduces photosynthetic capacity by ionic effects.