Abstract: Dry biomass and changes of nitrogen (N) uptake and utilization in oilseed rape during vegetative growth stage at two levels of CO₂ (natural: 400 μmol·mol^-1, elevated: 700 μmol·mol^-1) and two levels of N application (normal: 15 mmol·L^-1, limited: 5 mmol·L^-1) were studied in a sand culture experiment. Results showed that plant height, basal diameter and dry biomass were increased under the elevated CO₂ concentration, and the increment of either basal diameter or dry biomass at the normal N level was higher than that at the limited N level, but the increased degree of plant height and root dry weight showed an opposite pattern. Regardless of the N application levels, root volume, total active absorption area were increased under the elevated CO₂ concentration, but number of the first lateral root was only increased at the normal N level, root length was only increased at the limited N level. N content in organs of oilseed rape was declined under the elevated CO₂ concentration, and the declined degree of N contents in leaves and roots was significantly higher than that of stems. Under the elevated CO₂ concentration, accumulation amount of N in roots, stems and leaves were increased at the normal N level, only increased in stems at the limited N level, and decreased in roots and leaves. N uptake efficiency, N use efficiency (NUE) and N efficiency were increased under the elevated CO₂ concentration, and increased degree at the normal N level was higher than at the limited N level, and the response of NUE to N application levels was more obvious.

Key words: extractable carbon, grazing, mowing, microbial biomass., extractable nitrogen