Impact of chloride on nitrate absorption and accumulation by broccoli (Brassica oleracea var. italica)

Abstract

In the present study, we tested the hypothesis that continuous chloride treatment decreases nitrate absorption and accumulation by broccoli (Brassica oleracea var. italica) plants. In a field experiment, both fresh and dry weights of shoot and inflorescence increased linearly with increasing nitrogen applied (70–130 kg ha−1). Chloride application (0–450 kg ha−1) did not significantly affect the final yield. In a greenhouse experiment in which the plants were grown in soilless culture and supplied with 10–18 mmol L−1 nitrate, only the fresh weights of shoot and inflorescence decreased linearly with increasing chloride application (0–45 mmol L−1). In both experiments, increasing chloride application slightly decreased the concentrations of nitrate nitrogen and total nitrogen in xylem sap, and increased the chloride concentrations of both xylem sap and phloem exudate and the total-nitrogen concentration of phloem exudate. The shoot-nitrate contents increased with increasing nitrogen application and decreased with increasing chloride application, whereas the shoot-chloride contents increased with increasing chloride application and decreased with increasing nitrate application. The total-nitrogen contents of the shoot were not affected by chloride application. These data are interpreted to suggest that nitrate absorption was not inhibited by the presence of chloride in the growing medium and that the decrease in nitrate accumulation of the shoot resulted from the stimulation of organic-nitrogen formation from absorbed nitrate. Key words: Antagonism, broccoli, chloride, interaction, nitrate