Canola cultivars differ in nitrogen utilization efficiency at vegetative stage

Abstract

Previous research indicated genotype-specific responses in nitrogen utilization efficiency (NUE) for oilseed rape ( Brassica napus L.), but mechanisms behind those differences are unknown. Our objective was to determine whether cultivar variations in NUE (dry matter production per unit of N absorbed) could be related to the differences in N and nitrate uptake and partitioning. Four Australian spring canola cultivars (Eyre, Charlton, Pinnacle and Rainbow) were grown in glasshouse under conditions of low- and high-N supply. All cultivars were at the same growth stage when harvested 60 days after sowing (rosette stage with five leaves at low-N supply and nine leaves at high-N supply). Cultivars significantly differed in total N uptake in roots and shoots, but not when the whole plants were considered. Although all cultivars had similar total N uptake per plant, significant differences in NUE existed because of differences in plant biomass. N-efficient cultivars Charlton and Rainbow produced larger plant biomass and had lower N concentration in various aboveground plant parts (including dead leaves) than N-inefficient cultivars Pinnacle and Eyre. Nitrogen concentration in roots did not differ significantly among cultivars. Regardless of N supply, N concentrations in various plant parts were in the order: young blades > old blades > roots > young petioles > stems > old petioles > dead leaves. No significant variation in nitrate-N concentration in roots or various aboveground plant parts was found among tested cultivars. The absence of cultivar × N treatment interaction for plant dry weight, N concentration, N uptake, and consequently NUE, clearly indicated that cultivars that performed best at high-N supply also showed similar responses under N-deficient conditions. Despite similar total N uptake per plant, significant differences in NUE existed because more N-efficient cultivars produced larger plant biomass and tended to have lower N concentrations in all plant parts (except roots) compared with less N-efficient cultivars.