The response of grain yield and ear differentiation related traits to nitrogen levels in maize varieties with different nitrogen efficiency.

Maize (Zea mays L.) is one of the most widely distributed and important crops in China. Maize ear differentiation plays an important role grain yield formation. However, it is unclear if ear and root morphophysiology status affects yield formation by altering ear differentiation and development under different nitrogen (N) conditions. The aim of this study is to understand how the ear differentiation and development are affected by ear and root morphophysiology traits, as affected by the N rate. The experiment consisted of two N rates: high nitrogen (180 kg ha), and low nitrogen (60 kg ha). Two N-efficient varieties (NEVs) and two N-inefficient varieties (NIVs) were grown in the field. The results showed higher nitrogen accumulation and grain yield in NEVs than in NIVs, which was mainly attributed to the increased N uptake by the larger root system under both N conditions. Under high N conditions, among ear differentiation-related traits, only FR was significantly positively correlated with grain yield, and NEVs ensure FR through higher N concentration and ZR content in ear at the fertilization stage. Under low N conditions, NEVs obtained higher FP, SR and FR through higher N concentration and IAA in ear at the early stage of ear differentiation, maintained lower AR and BTL by higher RA, R-ZR and E-ZR at the late stage of ear growth. These results suggest that NEVs have a more complex mechanism for obtaining higher grain yield under low N conditions than N sufficiency, and that phytohormones play an important role in this process.