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Title:Physiological role of mixed nitrogen nutrition in enhancing productivity of maize
Author(s):Smiciklas, Kenneth Donald
Doctoral Committee Chair(s):Below, Frederick E.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Agronomy
Biology, Plant Physiology
Abstract: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 $\mu$mol 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 $\mu$M 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.
Issue Date:1991
Rights Information:Copyright 1991 Smiciklas, Kenneth Donald
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9136737
OCLC Identifier:(UMI)AAI9136737

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