Effect of nitrogen fertilization and Bacillus licheniformis biofertilizer addition on the antioxidants compounds and antioxidant activity of greenhouse cultivated tomato fruits (Solanum lycopersicum L. var. Sheva)

Abstract

Tomato is one of the principal crops worldwide due to its large consumption. In this work, biofertilization treatments, based on Bacillus licheniformis, with different nitrogen fertilization doses were investigated to improve the functional quality of tomato under greenhouse conditions. Treatments tested used nitrogen fertilization only (NF) or nitrogen combined with biofertilization (BF) with the following nitrogen doses: 0, 25, 50, 75 and 100% of the recommended nitrogen dose. The lycopene content increased with the nitrogen dose with the BF treatments resulting in lower lycopene contents in comparison with the NF counterparts. The contents of hydrophilic antioxidant compounds (vitamin C and total phenols), as well as antioxidant activity (DPPH scavenging capacity and FRAP) increased as the nitrogen dose was reduced. The biosynthesis of the hydrophilic antioxidant compounds appears to be an induced resistance mechanism caused by the nitrogen-deficiency stress. In addition, B. licheniformis had a positive net effect on the synthesis of flavonoids by the plant at a 75% nitrogen dose. A two-factorial ANOVA (nitrogen fertilizer dose×biofertilizer addition) evidenced that the greatest contribution of the nitrogen fertilizer dose was to the total phenols content and antioxidant activity, while the biofertilizer mainly contributed to the vitamin C and lycopene contents. In general, the content of antioxidant compounds was affected by the interaction of the two factors. Significantly, this is the first report about the combined effect of the nitrogen fertilization dose and biofertilization addition during tomato cultivation, on the content of antioxidant compounds in tomato fruits.