Inhibition by NaCl of Net CO2 Fixation and Yield of Cucumber

Abstract

Cucumber (Cucumis sativus L. cv. Fidelio) grown in sand culture in the greenhouse was trickle-irrigated with nutrient solution containing 0, 10, or 50 m m NaCl. Gas exchange of Individual leaves was measured by a portable infrared gas analyzer et saturating photosynthetic photon flux. Salt at 10 m m had no detectable effect on plant performance, but exposure to 50 m m NaCl caused net CO 2 fixation to decline by 33% and 48% in the eighth and ninth oldest leaves, respectively. Stomatal conductance and transpiration rate were also reduced (≈ 50%) In these leaves. These differences, as well as lower leaf water potentials, were associated with a 60% reduction in fruit fresh weight. The relationship between net CO 2 fixation and intercellular (substomatal) CO 2 concentrations was determined for individual, attached leaves of plants with roots exposed to various concentrations of NaCl in hydroponics. With 50 and 100 m m NaCl, a nonstomatal contribution to the inhibition of photosynthesis at the chloroplast level was Indicated by strong inhibition of CO, fixation at a saturating CO 2 concentration. Salt-induced inhibition of CO 2 fixation was associated with accumulation of Na+ and Cl-, and lower K+ in the individual leaves examined.