Effect of salinity stress on photosynthesis and related physiological responses in carnation (Dianthus caryophyllus)

The effect of salinity stress on growth and photosynthesis has been studied in various plants. However, reports on the impacts of salt stress on the growth and physiological factors in carnation are limited. In this study, we measured how photosynthesis and related parameters were affected by salinity stress at the flowering stage of carnation. Salinity reduced the photosynthetic rate and related parameters, including stomatal conductance, intercellular CO2 concentration, and transpiration. Chlorophyll content slightly increased at lower NaCl concentrations, and showed a decreasing tendency at higher NaCl concentrations. ABA content increased with increasing NaCl concentrations. The duration and extent of sap flow significantly decreased at higher NaCl concentrations compared to the untreated control on both sunny and cloudy days. At 200 mM NaCl, stressed leaves appeared to have smaller cell size and larger intercellular spaces. Stomata subsided at lower and upper epiderma, while stomatal size and density decreased at higher NaCl. Epicuticular wax layer was particularly thicker at 200 mM NaCl and some stomata were completely covered with the epicuticular wax. Hence, the results reported here facilitate a better understanding of the potential salt tolerant mechanism adopted by carnation to reduce transpirational water loss from the plant under salt stress. Overall, the reduced photosynthetic capacity under salinity stress could be attributed to a decreased stomatal conductance.