Ammonium/nitrate ratio affects the growth and glucosinolates content of pakchoi

Resumo

Nitrogen (N) strongly affects plant growth. However, little is known about the effects of the ammonium/nitrate ratio on pakchoi, especially its glucosinolates (GSs) content. The aim of this study was to evaluate the effects of a constant N supply (8 mM) but with five ammonium/nitrate ratios on the growth of pakchoi in a hydroponic system in 2 years. In both years, a higher biomass (dry weight) was in the 4/4 and 2/6 ammonium/nitrate treatments, respectively, with no significant difference in biomass between these two treatments. The biomass then decreased with increasing proportions of ammonium in the N supply. The N and sulfur contents were strongly affected in the sole nitrate or ammonium treatments, as were the contents of chlorophyll, lutein, and β-carotene. Most of the individual GSs detected in pakchoi showed the highest concentrations in the sole ammonium treatment. The ammonium/nitrate ratio also affected the types of GSs. The highest proportion of indolyl GSs and the lowest proportion of aromatic GSs were in the sole ammonium treatment. We concluded that a high ammonium level decreases the biomass but increases the GSs concentrations in pakchoi. Further studies are required to explore the difference in GSs metabolism among plants supplied with different ammonium/nitrate ratios.