Physiological mechanisms underlying post‐silking nitrogen use efficiency of high‐yielding maize hybrids differing in nitrogen remobilization efficiency

Abstract

AbstractIt is a great challenge to increase nitrogen (N) remobilization from leaves while ensuring high grain yield of maize (Zea mays L.). One possible way is to increase photosynthetic N use efficiency (PNUE) of leaves during post‐silking. This study aimed to understand the strategies required to maintain high PNUE during post‐silking in a N‐remobilizing high‐yielding maize hybrid. In this study, the high‐yielding hybrid XY335 with high N remobilization efficiency (NRE) and the high‐yielding hybrid ZD958 with low NRE were used in a three‐year field experiment under normal N levels. The results show that specific leaf N contents were similar in lower, middle, and upper leaves of the two hybrids from silking stage to maturity. Throughout the grain filling period, net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration, and PNUE of XY335 were similar to that in ZD958 in lower leaves, but higher in middle and upper leaves. Stomatal density and maximum rate of carboxylation in upper leaves and maximum rate of electron transport in middle leaves was higher in XY335 than that in ZD958. It is concluded that maintaining the PNUE of lower leaves together with increasing the PNUE of middle and upper leaves at canopy‐level are the possible regulatory mechanisms to improve NRE without penalty in whole‐plant photosynthesis during post‐silking in modern high‐yielding cultivars. The higher PNUE is at least partly related to the higher proportion of N allocation to the carboxylation and bioenergetics systems and the higher stomatal density and greater gs. Therefore, genetic improvement in N allocation to the carboxylation and bioenergetics systems and stomatal density and gs might increase PNUE.