Effect Of Carbon-Nitrogen Metabolism On Kernel Number In Summer Maize (Zea Mays L.)

Growth and development of summer maize (Zea mays L.) under different plant densities, different nitrogen (N) supply rates, or different plant densities with different N supply rates were studied in field condition. Effects of spikelet differentiation, silk development, dry mater production, partition and remobilization, carbon-nitrogen (C-N) metabolism, and kernel development in different ear position on kernel set were investigated. The mechanism of C-N metabolism affecting kernel number (KN) and ways of promoting apical kernel development were discussed.Maize grain yield was closely associated with KN and this yield component was very sensitive toenvironmental conditions. Increasing KN was required for high grain yield in high plant density. KNvaried most with kernels per row, length of aborted part of the ear and aborted kernels. N supply(120~240 kg/hm2) increased KN and grain yield by promoting apical kernel development, reducinglength of aborted part of the ear and number of aborted kernels while N deficiency resulted contrarily.KN depended on the number of fertilized spikelets that survived and formed mature kernels, which differed most with environmental changes, rather than on the total number of differentiated spikelets, which were usually stable. The number of aborted kernels was reduced, the number of fertilized spikelets that set kernels, and therefore KN was increased by N supply (120-240 kg/hm2) . The growth and development of silk and ear, which were influenced by N supply, also affected KN.KN had a close relationship with plant dry matter production, and related positively with plant growth rate (PGR) during the period, about one month, bracketing flowering. N supply (120~240 kg/hm2) increased PGR bracketing flowering, therefore produced more assimilate to kernel growth and kernel set. C and N metabolism and their interaction affected KN through C assimilation and direct effects on enzymes. N supply resulted in NR, GS, and SPS activity increased, C-N metabolism enhanced, more assimilate produced and distributed to kernels, which lead to more kernels.The development of apical kernels differed strongly with mid-basal kernels in kernel weight, kernel volume, dry matter accumulation, and grain filling rate at early stage. Suffering from disadvantageous position in the ear, the abortion of apical kernels related to less assimilate availability and lower kernel sink activity. N supply( 120~240 kg/hm2) contributed to KN by increasing the total content of soluble sugar, the content of sucrose, and the activity of enzymes related to sucrose inverting and starch synthesis in apical kernels.A synchronous pollination between apical and mid-basal spikelets delayed the development of apical kernels, which resulted in kernel abortion in some terns. Fortunately, apical kernel abortion could be partially overcome by artificially synchronized pollination, which weakened the dominance of mid-basal kernels on apical kernels.In this experiment, the optimum densities and N supply rates for summer maize Zhengdan 958 were 82500-97500 plant/hm2 and 180-240 kg/hm2. N availability both in big trump stage and in silk stage was favorable.