Gas exchange, water relations, and Ion concentrations of salt‐stressed tomato and melon plants

Abstract

Tomato and melon plants were grown in a greenhouse and irrigated with nutrient solution having an EC of 2 dS m⁻¹ (control treatment) and 4, 6, and 8 dS m⁻¹, produced by adding NaCl to the control nutrient solution. After 84 days, leaf water relations, gas exchange parameters, and ion concentrations, as well as plant growth, were measured. Melon plants showed a greater reduction in shoot weight and leaf area than tomato at the two highest salinity levels used (6 and 8 dS m⁻¹). Net photosynthesis (Pn) in melon plants tended to be lower than in tomato, for all saline treatments tested. Pn was reduced by 32% in melon plants grown in nutrient solution having an EC of 4 dS m⁻¹, relative to control plants, and no further decline occurred at higher EC levels. In tomato plants, the Pn decline occurred at EC of 6 dS m⁻¹, and no further reduction was detected at EC of 8 dS m⁻¹. The significant reductions in Pn corresponded to similar leaf Cl⁻ concentrations (around 409 mmol kg⁻¹ dry weight) in both plant species. Net Pn and stomatal conductance were linearly correlated in both tomato and melon plants, Pn being more sensitive to changes in stomatal conductance (g_s) in melon than in tomato leaves. The decline in the growth parameters caused by salinity in melon and tomato plants was influenced by other factors in addition to reduction in Pn rates. Melon leaves accumulated larger amounts of Cl⁻ than tomato, which caused a greater reduction in growth and a reduction in Pn at lower salinity levels than in tomato plants. These facts indicate that tomato is more salt‐tolerant than melon.