Abstract: 【Objective】The study is designed to put forward the physiological indexes of high and stable yield in maize and explore the new management ways by comparing the differences of carbon and nitrogen metabolism of different maize varieties under different nitrogen levels and analyzing its coordination. 【Method】 The study was carried out to compare the differences of yield, the staying-green duration of leaf, nitrogen uptake and translocation, the ratio of C/N, PEP carboxylase and RUBP carboxylase activity by field and pot experiments in Wenxian and Zhengzhou from 2009 to 2011, in which 4 varieties of summer maize, including ZD958, ND108, XD20 and YD2002, were planted at 60 000 plants/hm² under four nitrogen levels of 0, 120, 240, 360 kg·hm^-2.【Result】(1) The grain yield of 4 maize varieties increased significantly with nitrogen level increasing. In pot experiments, the yield gap of XD20 between different nitrogen levels was the biggest, and that of ZD958 was the smallest. However, under the field condition, the difference of maize except XD20 between N240 and N360 was not significant. (2) The comparison of nitrogen uptake and translocation during grain-filling stage indicated that the nitrogen in ZD958 vegetative organs could be preferentially transferred to the leaves under low nitrogen condition which contributed to the longer staying-green duration of maize leaf. For ND108, both of nitrogen uptake and translocation were larger, thus its leaf can also stay green longer, but the effective utilization of nitrogen was lower. For XD20, due to lack of mechanism of priority supply to leaves and lower N uptake of under low nitrogen condition, the leaf showed early senescence. For YD2002, because of larger nitrogen transfer amount from vegetative organs to grain under four nitrogen levels and smaller nitrogen absorption in root, the leaf also showed early senescence. (3)During the grain filling stage, the C/N ratio of leaf in ZD958 and XD20 were between YD2002 and ND108 in the condition of normal fertilization. For the mature stage, the grain C/N ratio of ZD958 and XD20 were higher than the other two varieties. (4)At mid filling stage, ratio of PEPCase and RUBPCase of ZD958 was significantly higher than the other three cultivars, that of YD2002 was lower, and that of XD20 and ND108 increased significantly with the increase of nitrogen fertilizer. 【Conclusion】The excellent coordination of carbon and nitrogen metabolism of maize was reflected in the translocation process of carbohydrate and nitrogen. The maize that be able to coordinate the contradiction between grain and vegetative organ demand for carbohydrate and nitrogen, and with a higher PEPCase/RUBPCase, could reach a high and stable yield.

Key words: maize, carbon metabolism, nitrogen metabolism, C/N, PEPCase, RUBPCase