Comparison of whole system of carbon and nitrogen accumulation between two maize hybrids differing in leaf senescence

A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (N-c) in the leaves and a higher specific N absorption rate by roots (SAR(N)), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and N-c, and between the photon-saturated photosynthetic rate (P-sat) and N-c were lower in P3845. The P-sat per unit N-c in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high P-sat per unit N-c in the leaf. Consequently, a high P-sat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves.