Accompanying ions of ammonium sources and nitrate : ammonium ratios in tomato plants

Abstract

The tomato (Solanum lycopersicum L.) cultivar Micro-Tom (MT) is widely used in physiological studies, but the effects of nitrate (NO3 -) and ammonium (NH4 +) ratios (NO3 - : NH4 + ratios) and, in particular, the effects of the accompanying ions in NH4 + sources are unknown. To determine whether the accompanying ions in NH4 + sources influence NH4 + toxicity, the effects of NO3 - : NH4 + ratios on the physiology, electrolyte leakage index, nutrition, and dry weight were studied using hydroponics. The NH4 + sources were ammonium chloride (NH4Cl) or ammonium sulfate [(NH4)2SO4], and five NO3 - : NH4 + ratios were used: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. The NH4 + source was calcium nitrate [Ca(NO3)2], and the nitrogen (N) concentration was 15 mmol L−1. The results indicate that NH4Cl or (NH4)2SO4 can be used in studies on NH4 + toxicity because the accompanying ions did not influence the tomato plants. In addition, NO3 - : NH4 + ratios of 100 : 0 and 75 : 25 resulted in the highest dry weight of tomato plants, whereas ratios of 25 : 75 or 0 : 100 were toxic.