Beneficial effects of silicon in alleviating salinity stress of tomato seedlings grown under sand culture

Sand culture experiments were designed to investigate the effect and mechanism of exogenous silicon on salt tolerance of tomato plants. Plant growth, photosynthetic gas exchange, water status, ion accumulation, root morphological traits, root water uptake and antioxidant defense were analyzed under 150 mM NaCl without or with application of 2 mM silicon. Application of silicon improved tomato growth, photosynthetic pigment and soluble protein contents, net photosynthetic rate and root morphological traits under salt stress. The leaf transpiration rate and stomatal conductance were not decreased, but increased by application of silicon under salt stress. Meanwhile, silicon decreased the concentrations of Na and Cl in the roots, stem and leaves, but without any sign of decrease in the root-to-shoot translocations. Leaf water status, root hydraulic conductance and antioxidant ability were all improved by exogenous silicon under salt stress. Results suggest that silicon application could decrease Na and Cl accumulation and increase antioxidant defense in tomato roots, which improved the root growth and hydraulic conductance, and therefore improved leaf water status and shoot growth. The study also suggests a potential value of silicon application in soilless culture (sand culture) in tomato production.