Differences in nitrogen use efficiency among different rape varieties and their physiological basis

Differences in nitrogen (N) use efficiency and their physiological basis among different rape (Brassica napus L.) varieties were studied using N efficiency coefficient, i.e. the ratio of seed yield in N stress condition to that in normal N supply in a pot experiment. Results showed that there were significant differences in N use efficiency (NUE) among five rape varieties, with NUE coefficient varying from 0.37 to 0.69. Under N stress condition, the variety 231 was high NUE variety with the highest seed yield and NUE coefficient, but the variety Bin27 was low NUE variety with the lowest seed yield and NUE coefficient. Under normal N supply condition, the variety 742 was high yield potential variety with the highest seed yield, whereas the variety Huiyou 50 was low yield potential variety with the lowest seed yield.Under N stressed condition, N content and accumulated uptake in rape variety with high NUE were greater than those of the varieties with low NUE. Under normal N supply condition, N content in high yield potential variety was lower than that of low yield potential variety. Because of higher biomass in high yield potential variety, its accumulated N uptake was not lower than that of low yield potential variety, even higher during the seedling stage, indicating that high NUE variety was closely related to its N uptake capacity, and the high yield potential variety was closely related to the capacity of dry mass accumulation.Under N stress condition, leaf chlorophyll content and nitrate reductase activity, and stem and leaf soluble sugar content and reuse nitrate content in high NUE variety were greater than those of low NUE variety. Under normal N supply condition, leaf chlorophyll content and nitrate reductase activity, and stem and leaf soluble sugar content and reused nitrate content in high yield potential variety were higher than those of low yield potential variety, which indicated that the above-mentioned four physiological indices could be used as indirect indicators for assessing high NUE and yield potentiality.Under N stress condition, the difference of reused nitrate between the high and low NUE varieties may largely be due to difference of nitrate uptake capacity. But under normal N supply condition, the difference of reused nitrate between high and low yield potential may mainly be attributed to the reused capacity of nitrate.