Higher yields of modern maize cultivars are not associated with coordinated light and N distribution within the canopy

Canopy architecture and associated light distribution, nitrogen distribution, and leaf physiological characteristics drive canopy photosynthesis, and ultimately determine grain yields. Breeding has increased those yields during the past decades of breeding history but it is not clear if this also improved efficiency in nitrogen allocation for optimal light use. To what extent has selection for yields affected maize canopy architecture and the vertical distribution of light and nitrogen? A 2-year field experiment was conducted in Jilin province, Northeast China, involving six maize cultivars released between 1950 and 2004. The canopy architecture, the vertical distribution patterns of light and nitrogen, and grain yields of these cultivars were quantified and analysed. The genetic gain in grain yield through breeding was 109 kg ha−1 year−1, and the concomitant increase in aboveground biomass was 16.1 g m−2 ground year −1 at maturity stage. Modern cultivars had more erect leaves compared to older cultivars, especially the leaves above the ear leaf, showing a decrease of 0.31° year−1. The changes in leaf area index (LAI) and leaf angle contributed to the improved light distribution within the canopy over generations of selection, as the light extinction coefficient KL decreased significantly by 0.67% year−1. The canopy nitrogen content increased by 0.09 g N m−2 ground year−1, but the average canopy specific leaf nitrogen (canopy N/LAI) tended to decrease. The relationship between light and nitrogen distribution within the canopy differed among cultivars but did not relate to year of release(YOR), indicating that breeding of maize cultivars from the 1950–2004 primarily led to changes in canopy N and canopy architecture and did not improve the coordination between light and nitrogen in maize canopy. Yield gain through breeding history from 1950 to 2004 was strongly associated with increases in canopy N and LAI linked to increasing erectness of leaves, which improved light distribution under these conditions. In contrast, the coordination of light and nitrogen distribution was not changed much. We conclude that the higher yields that are obtained with modern cultivars do not appear to rely on a coordinated light and N distribution within the canopy.