Acidic Medium pH Mitigates the Effects of Long-Term Salinity on the Physiology, Biochemistry, and Productivity of Tomato ( Solanum lycopersicum L.) Plants

Salinity is one of the destructive abiotic stresses that limit the production of agricultural products. The medium acidity can impact ion uptake, the oxidation-reduction balance, and the solubility of the elements. The alleviative effects of the medium pH adjustment (unadjusted as control [pH ~ 8.5–9], pH 5.5, and pH 4.5) on adverse effects of salinity in tomato plants ( cv . Mobil) were examined in soilless culture. Plant growth, biochemical traits, and fruit attributes were evaluated. Leaf chlorophyll content ( chla+b ) was increased at pH 5.5, decreased at pH 4.5, and remained constant in the control plants. The highest leaf chla+b was recorded at pH 5.5, 42 days after stress onset (DAS). Lowering the medium pH reduced leaf DPPH and leaf phenol content by ~ 55 and 45%, respectively, compared with the control. The highest root K + content and the lowest root Na + /K + ratio were observed in plants grown at pH 5.5. The greatest leaf area, shoot and root dry weight (DW), and root length were observed at pH 5.5, increasing by 100, 23, 8, and 32%, respectively, compared with the control. Plants grown under pH 5.5 showed the highest number of fruits and fruit dry weight; lowering the medium pH increased the number of fruits and fruit DW by 77 and 32%, respectively, compared with the control. Generally, the medium pH adjustment at 5.5 enhanced the salinity tolerance of tomato plants. The results showed that lowering the medium pH could be a feasible approach to ameliorate the adverse effects of salinity on the growth and yield of tomato plants. Graphical Abstract