Silicon enhances the tolerance to moderate NaCl-salinity in tomato grown in a hydroponic recirculating system

Abstract

Salinity is a major threat to the productivity of agroecosystems as it affects the soil structure and the osmotic potential of the soil solution, resulting in nutritional imbalances, Na toxicity and reduction in crop growth and yield. As Silicon (Si) has been considered a beneficial element for alleviating plant stress, the present study was performed to determine if it could enhance tomato plant tolerance to NaCl-salinity in a closed-loop hydroponic system. Plants were irrigated with solutions containing 0, 20 or 60 mM NaCl combined with 0 or 1.50 mM Si. Shoot dry weight and fruit yield decreased with salinity, however, Si partially restored biomass and yield when the solutions contained 20 mM NaCl. Shoot and root K decreased with salinity, however, supplementary Si restored K in plants with 60 mM NaCl. Root and shoot Si was unaffected by NaCl or Si, however, shoot Na increased. Nonetheless, compared to non-Si plants, Si-treated plants showed a 19% and 32% lower shoot Na concnetration in 20 and 60 mM NaCl-plants, respectively. Silicon partly alleviated the K/Na imbalance caused by salinity. Increased shoot K/Na and Ca/Na balances were correlated with higher shoot biomass. Supplemental Si allowed an 80% increase in peroxidase activity and proline in plants with 60 mM NaCl. Fruit yield under moderate salinity was partially restored by Si, due to an increased root Na exclusion, lower shoot Na, and improved K, Ca and K/Na balance, which was correlated with increased shoot growth, POD activity and proline concentration.

Keywords:

• antioxidant enzymes
• electrical conductivity
• proline
• reactive oxygen species