The Response of Halophyte Tetragonia tetragonioides (Pallas) Kuntz. and Glycophyte Lactuca sativa L. Crops to Diluted Seawater and NaCl Solutions: A Comparison between Two Salinity Stress Types

The use of seawater in horticulture is underestimated. Although pure seawater is harmful to most living plants, diluted seawater could represent a promising integration to meet the crop's nutrient and water requirements. In the current trial, we compared the effects of moderate and high concentrations of seawater and a comparable NaCl solution on a salt-tolerant (Tetragonia tetragonioides) and a salt-sensitive (Lactuca sativa) crop grown in hydroponics. We tested the hypothesis that, due to its mineral composition, diluted seawater would result in a less stressful growing medium than NaCl. We observed that diluted seawater resulted in a less detrimental growing medium compared to an EC-comparable NaCl solution, with remarkable differences between the salt-tolerant and the salt-sensitive species. While the growth rates in Tetragonia did not vary between the two types of stress, diluted seawater led to a higher FW and DW biomass yield in the salt-sensitive lettuce compared to the NaCl treatment. Moreover, NaCl reduced the water consumption and water productivity in Tetragonia. In lettuce, NaCl-treated plants demonstrated lower water use efficiency and water productivity compared to the EC-comparable seawater treatment. Physiological parameters and the concentration of mineral elements, phenolics and proline also demonstrated that, due to different mineral composition, seawater is a less stressful growing medium compared to a NaCl solution at comparable EC.