Abstract: ： In order to explore the response of nitrogen （N） uptake and root traits of rapeseed （Brasscia napus L.） to the low N stress, two conventional rapeseed varieties, “814” and Xiangyou15, with hydroponics cultured, were used as experimental material, and three nitrogen treatments 10, 3 and 1 mmol/L NO₃^- were set up with 10 mmol/L as control. The amount of N absorbed and its N-uptake efficiency of repseed were determined as well as the root-shoot ratio, root volume, root absorbing area, root diameter, the whole root length and the branching number were assayed. The correlation between the N-uptake efficiency and root morphological characters were analyzed. Moreover, the root activity and the activity of H⁺-ATPase in root plasma membrane were measured. The results showed that the amount of N absorbed by rapeseed was decreased, but the N-uptake efficiency increased under low-N stress. The roots of rapeseed were elongated and showed more branches with lower root volume and higher root absorbing area in the low-N treatments compared with the control. The root activities showed no significant difference between the treatment with control and the treatment with 3 mmol/L NO₃^- supplied, however, the root activity showed significantly decreased with 1 mmol/L NO₃^- supplied. Compared with normal N supplied, the activities of H⁺-ATPase in root plasma membrane of rapeseed were significantly increased under low N stress. It showed significant difference on the H⁺-ATPase activity of rapeseed among the treatments with 10 mmol/L, 3 mmol/L and 1mmol/L N supplied.

Key words: rapeseed （Brasscia napu L.）, low-N stress, root traits, N-uptake efficiency