Genetic improvement of nitrogen uptake and utilization of winter wheat in the Yangtze River Basin of China

Verifying the ongoing genetic improvement of nitrogen use efficiency (NUE) and determining the physiological basis of the improvement will aid breeders and agronomists in developing new wheat (Triticum aestivum L.) cultivars, with the aim of high yields and low N fertilizer requirements. A two-year field experiment was conducted with 32 wheat cultivars, which were bred or widely planted in the Yangtze River Basin from 1950 to 2005 under two N application rates (0 and 225 kgN ha(-1)) in Nanjing, China, to examine the improvement of N uptake and utilization, as well as its physiological basis. Grain yield, harvest index (HI), N recovery efficiency (NRE), and N agronomic efficiency (NAE) increased with cultivar development from the 1950s to the 2000s. N accumulation at maturity of modern cultivars was higher than for the older cultivars, which mainly resulted in increased N accumulation amount and N accumulation rate during the jointing to anthesis U-A) growth period. With cultivar development, the activities of nitrate reductase (NR) and glutamine synthetase (GS) in leaves increased at the booting and anthesis stages, while remained stable during the grain filling stage, indicating that N assimilation increased prior to anthesis, resulting in an increase in pre-anthesis N concentration and uptake in plants. Leaf N concentration (LNC) increased at anthesis, and the increase was larger than that observed in other organs. At maturity, LNC and grain N concentration (GNC) decreased, while the amount of N in stems, chaff, and the total plants increased, indicating that increased N in leaves at anthesis enhances N remobilization to grain. The N distribution amount to leaves at anthesis increased with cultivar development, but decreased at maturity. Post-anthesis N translocation amount and N translocation efficiency of vegetative organs increased, and the N translocation efficiencies of leaves were higher than those of other organs. NRE and NAE were positively correlated with grain yield, kernel number, kernel weight, HI, N uptake during the J-A growth period, and post-anthesis N translocation. Grain yield and HI were positively correlated with pre-anthesis N uptake, and N translocation of each organ, while there was no relationship with biomass or post-anthesis N uptake. Therefore, increased pre-anthesis N assimilation ability and post-anthesis N translocation were strongly associated with grain yield, and N uptake and utilization efficiency. (C) 2016 Elsevier B.V. All rights reserved.