Phytochemical Changes Induced by Different Nitrogen Supply Forms and Radiation Levels in Two Leafy Brassica Species

The effect of three different nitrogen (N) supply forms differing in their ammonium-to-nitrate (NH4:NO3) ratio (100% NH4, 50% NH4 + 50% NO3, 100% NO3) under three different levels of daily photosynthetic active radiation (PAR) (low, 5.0; medium, 6.8; high, 9.0 mol m(-2) day(-1)) on a range of desirable health-promoting phytochemicals in Brassica rapa subsp. nipposinica var. chinoleifera and Brassica juncea was determined. The 100% NH4 supply under medium PAR levels led to the highest concentration of glucosinolates based on a low nitrogen/sulfur ratio as well as high levels of carotenoids in the leaves of both Brassica species. However, the 100% NH4 supply under low and medium PAR levels resulted in low concentrations of flavonoids based on high N concentration in the leaves. Thus, the data provided here have strong implications for crop management strategies aimed at optimizing both the concentration and composition of a range of phytochemicals.