Salinity and ammonium/nitrate interactions on tomato plant development, nutrition, and metabolites

The interactions between NaCl and different NO3-:NH4+ ratios were investigated. Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse, in 120L capacity containers filled with continuously aerated Hoagland nutrient solution. Treatments were added to observe the combined effect of two NaCl levels (30 and 60mM) and three millimolar ratios of nitrate: ammonium (14:0, 12:2, 10:4) on growth, nutrition, and contents of chlorophyll and sugars. Saline treatments decreased growth, which was partly restored by NH4+ treatment. The leaf mineral 4 composition showed a marked effect of nitrogen (N) source, while salinity only affected NO3- concentration. Changing the NO3-:NH4+ ratio from 14:0 to 12:2 and 10:4 produced progressive increases in the concentrations of iron (Fe), chlorophyll, and reducing sugars in leaves. Therefore, the deleterious effect of salinity on biomass production can be minimized by the use of nutrient solutions containing higher NH4+ concentrations, since this seemed to be correlated with increases in nitrogen assimilation and the levels of Fe and chlorophyll.