Investigating the effect of different concentrations of sodium bicarbonate (alkalinity stress) on some varieties of cool crops in hydroponic system

In order to investigate the effect of different concentrations of sodium bicarbonate on performance of four major varieties of cabbage, a greenhouse a factorial experiment was conducted based on a completely randomized design with three replications and two factors, including variety in four levels (cauliflower, cabbage, Brussels sprouts and kohl rabi) and sodium bicarbonate in three levels (0, 10 and 20 mM). Germinated seeds at four-leaf stage were transferred to four-liter pots containing aerated nutrient solution. After growing for 30 days, seedlings were treated with sodium bicarbonate for two months. Results showed that leaf and root dry weight significantly decreased by increasing the sodium bicarbonate concentration. Chlorophyll a, chlorophyll b, Fv/Fm and PI decreased in all varieties as a response to enhancement of sodium bicarbonate concentrations. The lowest reduction in chlorophyll a and chlorophyll b was observed in cabbage and cauliflower. Osmosis regulation processes were activated in cabbage plants in response to increase in sodium bicarbonate concentrations, as increases in proline and soluble carbohydrate were observed in kohl rabi plants. Increase of sodium bicarbonate concentrations led to reductions in P, K, Mg, Fe, Zn and Mn as well as increase in Na and Ca in all plants. Sodium bicarbonate stress, at 20 mM, led to a significant reduction in Fe concentration in leaf and root, so that Fe concentration of leaf decreased 150 percent at this level compared to the control. In association with variety results, the greatest Fe concentrations were observed in kohl rabi and cabbage plants.