Effects of NaCl or Na2SO4 salinity on plant growth, ion content and photosynthetic activity in Ocimum basilicum L.

Basil (Ocimum basilicum L., cultivar Genovese) plants were grown in Hoagland solution with or without 50 mM NaCl or 25 mM Na2SO4. After 15 days of treatment, Na2SO4 slowed growth of plants as indicated by root, stem and leaf dry weight, root length, shoot height and leaf area, and the effects were major of those induced by NaCl. Photosynthetic response was decreased more by chloride salinity than by sulphate. No effects in both treatments on leaf chlorophyll content, maximal efficiency of PSII photochemistry (Fv/Fm) and electron transport rate (ETR) were recorded. Therefore, an excess of energy following the limitation to CO2 photoassimilation and a down regulation of PSII photochemistry was monitored under NaCl, which displays mechanisms that play a role in avoiding PSII photodamage able to dissipate this excess energy. Ionic composition (Na+, K+, Ca2+, and Mg2+) was affected to the same extent under both types of salinity, thus together with an increase in leaves Cl−, and roots SO42− in NaCl and Na2SO4-treated plants, respectively, may have resulted in the observed growth retardation (for Na2SO4 treatment) and photosynthesis activity inhibition (for NaCl treatment), suggesting that those effects seem to have been due to the anionic component of the salts.