Influence of NaCl-salinity imposed on half of the root system of hydroponically grown tomato on growth, yield, and tissue mineral composition

The effects of splitting the root system of tomato grown in recirculating nutrient solution into two compartments receiving raw water (0.3 dS m(-1)) and saline nutrient solution (13.0 dS m(-1), 100 mM NaCl), respectively, on growth, yield and tissue mineral composition were investigated. The water/salinity treatment was compared with standard nutrition for tomatoes (2.2 dS m(-1)) or supply of the entire root system with the above saline nutrient solution. The exposure of all or part of the root system to NaCl-salinity reduced the K concentration initially in the roots and, later, in the old leaves. The total-N concentration was restricted only in the older leaves by the exposure of all or half the root system to high NaCl concentrations. In all plant parts, the concentration of Na was more markedly raised when the entire root system was exposed to NaCl-salinity as compared with the root-splitting treatment. The P concentration was restricted in the part of the roots supplied solely with raw water. The leaf Ca and Mg concentrations were diminished on some sampling dates only when the entire root system was exposed to NaCl-salinity. Further, the root Mg concentrations were significantly increased in both root parts of plants subjected to root splitting as compared with those measured in plants receiving exclusively standard or saline nutrient solution. The obtained results indicated also an intensive retranslocation of K, Na, Mg and N between the two root compartments. The exposure of the entire root system of tomato to salinity depressed the fresh fruit yield mainly because of a restricted mean fruit weight but had no effect on the dry fruit production. Splitting the root system into two compartments receiving raw water and NaCl-enriched nutrient solution, respectively, also depressed the fresh fruit yield but to a slightly lesser extent than complete exposure to salinity. However, the yield decline was exclusively due to fewer fruits per plant, while the mean weight and the dry-matter content of fruit were not affected. As a result, the dry fruit yield was also markedly restricted in the water/salinity treatment. It is suggested that a moderate salt stress imposed on the entire root system of tomato restricts yield due to a lower water content of fruit owing to osmotic adjustment, while the exposure of the roots partly to salinity and partly to raw water diminishes the dry biomass production due to lack of osmotic adaptation.