In order to explore the physiological and relational mechanism early senescence of shoot and root underhigh planting density of super high-yielding spring maize, the regulating pathways of defending senescence andincreasing yield were explored. Using different plants and spike types, Xundan20, Neidan314 and Jingdan28 as materials,compared and studied the effects and relation of the different layers of leaves' photosynthetic characteristics andthe vertical changes of root activity in three kinds of plant density (75 000, 82 500 and 90 000 plants/ha) at anthesisand kernel stage. The results showed that the LAI of different layers of leaves increased with increasing density, whilethe SPAD value, Pn, Gs, Tr and root activity continuously were decreasing with increasing density, various traits ofXundan20 were more sensitive than Neidan314 and Jingdan28 on the density reaction. Xundan20 gained maximumyield in high-density and it’s significantly difference than middle-density and low-density. The maximum root activityof Xundan20 lay in 30 - 40 cm soil layer, while the maximum root activity of Neidan314 and Jingdan28 lay in the20 - 30 cm soil layer at grain filling stage. It was clear that the shoot and root systems were functionally closely relatedto the aging process, slowing down speed of root activity of Xundan20 was faster than Neidan314 and Jingdan28,which was intrinsically linked to the decline of the leaves' SPAD value, LAI, Pn, Tr and Gs. The progress of leafsenescence was the same with the root activity space down progress.

“973”计划项目(2009CB118601)、国家自然科学基金项目(31060175)、国家现代玉米产业技术体系(CARS-02)、内蒙古农业大学玉米超高产创新团队计划