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Below, Frederick E. Smiciklas, Kenneth Donald 2011-05-07T12:43:40Z 2011-05-07T12:43:40Z 10000-01-01 1991 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. Made available in DSpace on 2011-05-07T12:43:40Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9136737.pdf: 4583573 bytes, checksum: 164e7d6aa924069bf4ed3ac90575ecce (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:44:56Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:19:50-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9136737 (UMI)AAI9136737 http://hdl.handle.net/2142/20592 eng Copyright 1991 Smiciklas, Kenneth Donald Agriculture, Agronomy Biology, Plant Physiology Physiological role of mixed nitrogen nutrition in enhancing productivity of maize text Crop Sciences Crop Sciences University of Illinois at Urbana-Champaign Dissertation Ph.D.