published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Nitrogen use efficient (NUE) wheat varieties have potential to reduce input costs for growers, limit N runoff into water ways, and increase wheat adaptability to warmer environments. Previous studies have done little to explain the genetic basis for NUE and components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). Four studies were conducted to 1) determine genotypic stability of NUE under high and low N regimes and under warming 2) determine effect of warming on NUE 3) indentify QTL associated with NUE components 4) assess the utility of canopy spectral reflectance (CSR) as a high-throughput phenotyping device for NUE. Genotypic response to N stress or warming varied. Uptake efficiency was found to be more important than utilization efficiency to genotypic performance under high and low N environments and under warming. Selection under low N for NUpE and under high N for NUtE most efficiently identified NUE varieties. Uptake and utilization were lower under warming due to quickened development. No strong correlations between the CSR indices and NUE existed. No QTL were found to be significantly associated with NUE components. Further research into the mechanisms controlling NUE and to reveal plant response to N stress and under warming is necessary.

Complexes of the type MX(η²-NO₃)(CO)₂(PPh₃)₂, (M = Mo, X = Cl, Br; M = W, X = Br) were prepared from the reactions of MX₂(CO)₂(PPh₃)₂ with ammonium nitrate in acetone. The complexes were characterized by elemental analyses, ¹⁵N labelling, infrared and NMR spectroscopy. The nitrate ligand is bidentate and the complexes are seven-coordinate. Novel nitrite complexes of molybdenum and tungsten of the type M(NO₂)₂(PPh₃)₂ were prepared. The compounds were characterized by elemental analyses, ¹⁵N labelling, infrared and multinuclear NMR spectroscopy. Both NO₂ ligands are chelating and the two NO₂, PPh₃ and CO ligands are equivalent. Molybdenum dinitrosyl complexes were synthesized by the reduction of nitrate ions. The crystal structure of cis-dinitrosyl-cis-dichloro-trans-bis-(triphenylphosphine)molybdenum(II) was determined by x-ray diffraction. Both the nitrosyl groups are linear. Mo(NO)₂Cl₂(OPPh₃)₂ and Mo(NO)₂Cl(NO₃)(OPPh₃)₂ were synthesized by the reaction of MoCl(η²-NO₃)(CO)₂(PPh₃)₂ with NO in acetone/toluene mixture. The nitrosyl ligands are linear and the phosphineoxide ligands are cis to each other. The dinitrite complex Rh(NO)(NO₂)₂(PPh₃)₂ of the series Rh(NO)X₂(PPh₃)₂ (X - monodentate anions) was prepared as a direct derivative of Rh(NO)Cl₂(PPh₃)₂ by its reaction with sodium nitrite. The complex is square pyramidal with an apical nitrosyl ligand. The two NO₂ groups are present as the nitro and the nitrito group. Rh(NO)(NO₂)₂(PPh₃) reacted with oxygen and formed Rh(NO₃)₃(PPh₃)₂. The reaction of Rh(NO)(NO₂)₂(PPh₃)₂ with CO in acetonitrile produced Rh(CO)(NO₂)(PPh₃)₂. The complex Rh(CO)(NO₂)(PPh₃)₂ is square planar with the phosphine ligands in the trans positions.

Twelve F(,1) families of alfalfa (Medicago sativa L.) plants having different potential for nitrogenase activity, and the two parental populations were tested for response to mycorrhizal inoculation in a low-phosphate soil mixture in the greenhouse. The purpose of this study was to: (a) determine the effects of vesicular-arbuscular mycorrhizae on growth, nutrition and nodulation of these 14 populations, (b) determine if differences existed between the populations with regard to several morphological characteristics, and (c) determine if certain characteristics can be transmitted across generations. The 14 populations were evaluated under four treatments: control no Myorrhizae, no Rhizobium; Rhizobium alone; Mycorrhizae alone; and the combination of Mycorrhizae and Rhizobium. The growth parameters measured differed significantly among the treatments and among the 14 populations studied, and no significant interaction between the populations and the treatments were found. The dual Mycorrhizae and Rhizobium treatment significantly increased plant height at 30 days and 60 days after planting, leaf area per plant, and plant top-dry-weight at two harvest dates. Mycorrhizal inoculation, however, decreased specific-leaf-weight significantly. Nitrogen fixation parameters such as nodule mass score, fibrous root score, and nitrogenase activity were increased significantly by the dual inoculation of mycorrhizae and rhizobium. The 14 populations differed significantly in nodule mass score, fibrous root score, and nitrogenase activity. Mycorrhizal inoculation increased nitrogen fixation more than plant growth. Correlation coefficients indicated that increased Nitrogenase activity is positively correlated with increased nodule mass, increased fibrous root mass, greater top-dry-weight, and leaf area. A step wise multiple regression showed that 49% of the variation in nitrogenase activity can be explained by the variation due to nodule mass, fibrous root mass, top-dry-weight, and leaf area. Several morphological characters showed a heritable response. Plants selected for high nitrogenase activity and high top dry weight transmitted these characteristics to their progenies.

A fertility study was initiated at the Maricopa Agricultural Center in 1984 to determine how nitrogen levels influenced growth, development, and root yield of the potential domesticate, buffalo gourd (Cucurbita foetidissima). Nitrogen had little or no effect upon the following parameters: seedling emergence, early growth rates, specific leaf weights, individual root weights, consumptive water use, canopy organic N content, and nitrate and ash content of all organs. Percent root dry matter and total carbohydrate content dropped linearly as N was increased, whereas canopy dry matter production, root organic N content, petiole nitrate concentration, and leaf area indices exhibited a positive linear response. A quadratic response curve best fitted fresh weight root yields, total root dry matter and carbohydrate production, water use efficiencies, and final plant populations. A modest amount of N (84 kg ha⁻¹) provided maximum yield response in this feral species grown at 405,000 plants ha⁻¹.

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