Effect of potassium fertilization on the contents of antioxidants in three cocktail tomato cultivars

Tomatoes are an important source of health beneficial phytochemicals, which act as antioxidants such as ascorbic acid, phenolic compounds, carotenoids, and tocopherols. The content of antioxidants is influenced, among others, by abiotic stress factors, like the nutritional status. Potassium (K) is a macronutrient, which is essential for several physiological functions in plants, for example, translocation of assimilates, activation of enzymes, maintenance of turgescence, and stomata regulation. The aim of this study was to investigate the effect of increasing K fertilization on the concentration of antioxidants in cocktail tomatoes. Therefore, three tomato cultivars (Primavera, Resi, and Yellow Submarine), grown in an outdoor pot experiment, were fertilized with increasing K doses for two consecutive years. It was confirmed that antioxidants in tomato fruit can be affected by the K regime, but was also shown that other factors may reduce or even inverse those effects when cultivation takes place in an uncontrolled outdoor environment. Most consistent K fertilization effects were found for naringenin, p-coumaric acid and caffeic acid. However, enrichment of tomatoes with antioxidants by K fertilization is cultivar dependent and, therefore, general statements should be avoided.