Physiological role of mixed nitrogen nutrition in enhancing productivity of maize

Although the maize (Zea mays L.) plant can utilize either NH$\sb4\sp+$-N or NO$\sb3\sp-$-N, many studies have shown that mixed N nutrition (NH$\sb4\sp+$ + NO$\sb3\sp-$) can optimize productivity. However, the physiological processes that are beneficially altered by mixed N have not been elucidated. Therefore, studies were conducted to compare plant productivity traits under mixed N or predominantly NO$\sb3\sp-$ nutrition. Mixed N nutrition enhanced early season leaf area and leaf number, stimulated post-anthesis nitrate reductase activity, and lessened late-season chlorophyll degradation. Although NO$\sb3\sp-$-grown plants had equivalent or greater rates (approximately 5 to 10%) of canopy photosynthesis (P$\sb{\rm s}$) than mixed N plants, the duration of P$\sb{\rm s}$ was unaffected by N-form treatment at photosynthetic photon flux densities of 900, 1800 or mathematically integrated from 600 to 2100 μmol photon m$\sp{-2}$ s$\sp{-1}$. Despite the lowered rates of P$\sb{\rm s}$, a 5% increase in grain weight and dry matter accumulation were observed with mixed N nutrition. However, the physiological strategy used to achieve this increase varied as a function of genotype. For example, the hybrid LHE136 x LH82 increased the partitioning of dry matter to the grain, whereas LH74 x LH51 increased dry matter production when supplied with mixed N. Mixed N nutrition also increased whole shoot N content of all hybrids (range of 5 to 14%), because of greater efficiency of N uptake. In addition, mixed N nutrition decreased the magnitude of kernel abortion for the hybrid B73 x LH51, or increased the number of ovules per earshoot for the hybrid LH74 x LH82. The enhanced reproductive development observed under mixed N conditions may be related to the supply of cytokinin, a growth-regulating substance. Six applications of 22 μM 6-benzylaminopurine (a cytokinin) to the developing shoot of plants supplied with NO$\sb3\sp-$ increased grain production to that of mixed N plants. In addition, the endogenous supply of cytokinin to the shoot was greater for mixed N plants during vegetative growth. Based on data from these studies, the enhanced yield observed under mixed N conditions appears to be related to genotypic differences in assimilate partitioning, kernel development, N accumulation, and cytokinin supply.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Smiciklas, Kenneth Donald

Contributors dc:contributor

• Below, Frederick E.

• Agriculture, Agronomy
• Biology, Plant Physiology

Statement dc:rights

• Copyright 1991 Smiciklas, Kenneth Donald

Language dc:language

eng

Identifier

AAI9136737
(UMI)AAI9136737

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/20592