Effects of Nitrogen Application on Nitrogen Accumulation and Translocation as well as Their Heterosis in Different Organs of Hybrid Wheat

Nitrogen fertilizer is one of the most important factors to influence the nitrogen metabolism in different organs as well as the growth and development of wheat.In this study,six hybrids of wheat(Triticum aestivum L.) and their seven parents were employed to compare the nitrogen accumulation and translocation in different organs at various growth stages and further to study the heterosis of nitrogen utilization.The experiment was set by a split plot design with two replications under two levels of nitrogen applications 0 and 200 kg ha~(-1).Above-ground plant parts were harvested at 75,90,105,120,140 and 160 d after sowing,corresponding to stages of stem elongation,flag leaf emergence,heading,flowering,milk-ripe and maturity,respectively.The samples were partitioned into leaf,stem and sheath,stalk and chaff of spike,and grain,then microwaved for 4 min,and dried in an oven at 60℃.Nitrogen content of the hammermill-ground sample and grain nitrogen content were determined by near infrared reflectance spectrometry.The results showed that the nitrogen application significantly increased the amount of nitrogen accumulation and content of various organs,but didn't affect their change patterns.Leaves were the main nitrogen storage organ prior to anthesis while grains stored the largest amount of nitrogen post anthesis,followed by stem and sheath.Nitrogen application had no significant effects on the heterosis of nitrogen accumulation,but had a significant inhibitory effect on the heterosis of nitrogen content.With nitrogen application nitrogen translocation was greatly accelerated in leaves,but not in stems and sheaths,stalk and chaff of spikes.More than 90% of nitrogen translocation of total straw came from leaves.The contributions to nitrogen translocation efficiency and contribution ratio in all organs were the largest in leaves,the next in stalk and chaff of spikes,and there was no significant difference in the same organ whether nitrogen was applied or not.There was a positive heterosis in nitrogen translocation,translocation efficiency and contribution ratio of various organs when no nitrogen was applied,but a negative heterosis when nitrogen was applied,which indicates an inhibitory effect of nitrogen application on the heterosis of nitrogen translocation.