Effect of Nitrogen Supply Level in Rhizosphere on Growth and Nutritional Quality of Purple Pak-choi

Abstract:

In order to understand the effects of rhizosphere N supply on the growth and nutritional quality of purple pak-choi (Brassica campestris ssp. chinensis var. communis), the physiological and nutrition characters were studied treated with different levels of NH₄NO₃. The results showed that the fresh and dry weight, root activity, free amino acid content of purple pak-choi increased initially and then slightly decreased with the N level increment. Nitrate reductase (NR) activity, contents of chlorophyll, NO₃^- and soluble protein, and DPPH· radical scavenging rate increased, activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) isozymes showed upward trend, while the contents of relative anthocyanin, soluble sugar, vitamin C (Vc) and total phenols, and FRAP value decreased. Meantime, the fresh and dry weight of purple pak-choi treated with 75-300 mg L^-1 NH₄NO₃ was low. The fresh and dry weight treated by 1200 mg L^-1 NH₄NO₃ was lower than that by 600 mg L^-1 NH₄NO₃, more NO₃^- accumulated in plant led to decline of nutrient quality, and NH₄NO₃ deposited in rhizosphere. So, the optimum level of NH₄NO₃ was 600 mg L^-1 because of high fresh and dry weight, balanced nutrition and strong antioxidant ability.