What is the Behavior of Tomato Plants when Exposed to Transitional Conditions Between Zinc Sufficiency and Excess?

This study evaluated the impact of Zinc (Zn) doses on biochemical and growth attributes in tomato plants (Solanum lycopersicum L). The plants were cultivated under greenhouse conditions in two agricultural soils Inceptisol and Oxisol. The following doses of Zn were evaluated: Inceptisol: control, 20, 40 and 60 mg kg^− 1; Oxisol: control, 40, 80 and 120 mg kg^− 1. Mineral contents in aerial parts of plants, gas exchange, SPAD index, superoxide dismutase (SOD) and peroxidase (POD) activity, peroxide content of hydrogen, lipid peroxidation, root growth parameters and shoot and root dry mass production were evaluated. Plants accumulated dose-dependent Zn in their shoot tissues in both soils. This increase in Zn (60 mg Kg^− 1) in Inceptisol and (120 mg Kg^− 1) in Oxisol inhibited of dry mass production (-19.3% in Inceptisol and − 15.0% in Oxisol), photosynthesis (-17.0% in Inceptisol and − 18.8% in Oxisol), and root growth (-52.8% in Inceptisol and − 39.0% in Oxisol).This increase in Zn (60 mg Kg^− 1) in the tissues stimulated an increase in the activity of SOD (40.1%) and POD (102.9%) enzymes in plants grown in Inceptisol. The 20 mg kg^− 1 (Inceptisol) and 40 mg kg^− 1 (Oxisol) treatments were not efficient in promoting plant growth and development. Thus, this study indicated that the application of Zn, for nutritional purposes, must be carefully evaluated since its effects are variable, without benefit in doses considered sufficient and possibly toxic in high doses in tomato plants.