Benefits of high nitrogen fertilizer on nitrogen metabolism, nitrogen transfer rate, root system architecture and grain yield of wheat ( Triticum aestivum L.) under water deficit at heading stage

Water and nitrogen (N) fertilizer are the two main factors affecting wheat growth and yield. Spring wheat cultivars, Spitfire (drought sensitive) and Drysdale (drought tolerant), were used as materials for studying N metabolism physiological and molecular dynamics under water-deficit treatment at high-N level (180 kg hm −2 , i.e., 80 mg kg −1 ) vs. low-N level (22.5 kg hm −2 , i.e., 10 mg kg −1 ) at heading stage in this experiment. The results showed that the chlorophyll, soluble sugar, soluble protein and free amino acid contents; glutamine synthetase (GS), glutamate synthetase (GOGAT) and phosphoenolpyruvate carboxylase (PEPC) enzyme activities; gene GS1 expression; and grain yield were increased at high-N level compared to low-N level under water-deficient stress at heading stage in both cultivars. Relative expressions of genes GDH , GOGAT and PEPC were down-regulated in Spitfire under water-deficit treatment, but were up-regulated in Drysdale. The indicators of root system architecture, including root surface area, total root volume, root diameter and number of root tips and root branches, were increased at high-N level under water-deficient treatment in both cultivars, whereas total root length decreased. The root–shoot ratio of both cultivars decreased to low-N level under water-deficit treatment. The N transfer rate was significantly increased at high-N level after heading for water-deficit treatment. The grain yields of both cultivars were maintained by the high-N level under water-deficit treatment. Our results suggested a high-N level could alleviate the damage from water deficiency by activating genes/enzymes related to wheat carbon and N metabolism.