Effects of Ethylene-Chlormequat-Potassium on Leaf Nitrogen Assimilation after Anthesis and Early Senescence under Dif-ferent Planting Densities

Abstract

To explore the effects of ethylene-chlormequat-potassium (ECK) on the physiological mechanisms of nitrogen assimilation and early senescence in summer maize, and provide a theoretical basis for high and stable yields of summer maize under high plant density by chemical regulation technology in North China Plain, we conducted a field experiment using two varieties of Zhongdan 909 and Xundan 20 with different planting densities in 2013 and 2014. The results showed that increasing plant density significantly decreased the activities of nitrate reductase (NR) and glutamine synthetase (GS) after anthesis, glutamate oxaloacetic transaminase (GOT) activity at anthesis, and glutamate pyruvate transaminase (GPT) activity at 30 days after anthesis. The soluble protein and free amino acid contents at 20 days after anthesis, and the SPAD value at 10 days after anthesis were significantly decreased with increasing plant density. For both varieties, grain yield reached the highest under 7.5×10 plants ha, while decreased under the density of ≥ 7.5×10 plants ha. The higher density resulted in early senescence. ECK treatment significantly increased the activities of NR, GS, and contents of free amino acid, soluble protein and SPAD value during middle and late grain filling stages. ECK treatment also significantly improved the GOT and GPT activities under 7.5×10−10.5×10 plants ha. Under the density ≥ 7.5×10 plant ha, the yields of Zhongdan 909 and Xundan 20 compared with their own control were respectively 第 12期 卢 霖等: 乙矮合剂对不同密度夏玉米花粒期叶片氮素同化与早衰的影响 1871 increased by 5.59%−6.63% and 6.73%−8.10%. ECK treatment significantly increased the nitrogen assimilation key enzyme activity of ear leaf and its product content under different planting densities, promoted normal nitrogen assimilation and prevented early senescence under higher planting densities, therefore increased yield. Thus, an appropriate planting density combined with ECK application could be an important technique for achieving high grain yield for summer maize production in North China Plain.