Improvement of nitrogen use efficiency and the relationship with root system characters of maize cultivars in different years

ObjectivesRoot architecture and anatomical structure of maize decide its nitrogen use efficiency. The study on the renovation of root characters of maize cultivars released since early 1990s will provide a theoretical basis for selecting new variety of maize with high yield and high nitrogen use efficiency.

MethodsField and pot experiments were conducted, and 8 maize cultivars promoted since 1980s were used as materials.They were Yedan 13 (YD13), Nongda 108 (ND108), Zhengdan 958 (ZD958), Xianyu 335 (XY335), Jingke 968 (JK968), Zhongdan 909 (ZD909), Denghai 605 (DH605) and Denghai 618 (DH618). No nitrogen application and N 236.25 kg/hm² were designed in the field experiment, N 4.5 g/plant (HN) and 1.5 g/plant (LN) were for the pot experiment. Roots and plants samples were regularly collected, some root system indices, dry matter, nitrogen accumulation and distribution were determined.

ResultsThe yields and N accumulation amount of recent promoted maize varieties were higher than those of the previous ones. The average yield and N accumulation amount of the cultivars after 2000's (JK968, ZD909, DH605 and DH618) were increased by 14.7% and 11.7% under high N treatment, and 16.1% and 20.6% under low N treatment. The root dry weight, nodal root number, root length, root surface area and root volume showed trends of decreases in the first and then increases over time. The root dry weights of the1990's varieties (ND108 and ZD958) were decreased by 54.2% compared to the1980's variety (YD13) under the high nitrogen level, while the root dry weights of the varieties after 2000's were increased by 23.2% compared to the 1990's varieties and still lower than that of YD13. The number of seminal roots increased gradually with change of the varieties. The root cortical aerenchyma (RCA) for root cross-sectional area ratio increased with change of the varieties, but the number of cell files (CCFN) and cortical cell size (CCS) had no obvious tendency. The D95 (Root depth above which 90% of root length is locatted) of the cultivars after 2000's increased by 23.7% compared to those before 2000's, indicating that the depth of root penetration increased. There was a significant positive linear correlation between the N accumulation and D95 and RCA% under same nitrogen level, while the correlation between the N accumulation amount and the root respiration rate was exactly opposite.

ConclusionThe nitrogen uptake and use efficiency of modern maize cultivars are significantly higher than those of previous one. The increased number of seminal root is beneficial to maize seedling growth. The root volume in the deep soil is obvious increased. The increase in RCA% of current maize cultivars leads to reduced root respiration which is beneficial to the increase of yield.