Development of Canopy Apparent Photosynthesis among Maize Varieties from Different Eras

The studies on main maize varieties used popularly from 50′s to 90′s in China showed tyat the canopy apparent photosynthesis rate (CAP)rose, percentage of declined CAP and the rate of respiration in total CAP reduced, with the renew of maize varieties. The CAP of middle base leaves in modern maize varieties was evidently higher than that of old varieties at filling stage. Planting density was main factors influencing the CAP of maize. Under three planting density conditions, modern maize varieties had higher CAP, increased tolerance of high plant density, stronger adaptive faculty, richer source, larger sink and high yield.