Abstract
Increasing plant P supply has been shown to either increase or decrease the salt tolerance of many plants. Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in a continuously flowing solution culture system to investigate whether P fertilization modified the detrimental effects of NaCl at low constant P concentrations similar to those in soil solutions. Increasing P fertilization enhanced the tolerance of tomato plants to NaCl. At 0.1, 1.0, and 10 mM P, the NaCl concentrations that reduced yields of fruit by 50% were 58,72, and 130 mM, respectively. Salinity reduced foliar P concentrations. This may have been mediated partly through ionic strength effects, which decreased the activity of H2PO4−1 by about 40%. Plants grown under saline conditions had higher internal P requirements. When the NaCl concentration was increased from 10 to 50 and 100 mM, the corresponding concentrations of P in the youngest mature leaf required to obtain 50% yield were increased from 1.8 to 2.4 and 3.0 g kg−1. The change in internal P requirement was also evident by the relative severity of foliar symptoms of P deficiency in plants growing in the saline treatments at any given foliar P concentration. Adequate P nutrition was essential for effective ionic compartmentation. Under saline conditions, increasing the solution P concentration from 1.0 to 10 μM decreased Na and increased K concentrations in immature leaves but increased Na and decreased K in the mature leaves. Accumulation of ions for osmotic adjustment and restriction of Na and Cl accumulation in immature leaves appear to be involved in P enhancement of salt tolerance of tomato plants.