A native desert Rhizobium, AZ-M1, was isolated from a nodulated mesquite tree (Prosopis juliflora var. velutina) following inoculation of mesquite seed with a desert soil. This strain and a selected commercial strain (31A5) were used in a greenhouse study to determine their N fixation efficiency against applied N fertilizer. Strain AZ-M1 was a more efficient N fixer than 31A5. The survival rate of the two strains was tested in three different desert soils in a controlled laboratory study. The native strain AZ-M1 grew and survived in the soils over a period of one month. The commercial strain did not grow and the population decreased from 10⁸ cells gm⁻¹ of dry soil to below 10⁴ cells after 14 days. Soil factors affected survival of both strains. The competitiveness of the two strains was compared in a greenhouse experiment. The native isolate out competed strain 31A5 in nodule occupancy regardless of cell number when applied as a mixed inoculant. A high incidence of double occupancy was found in the root nodules when double strain inoculants were applied. The two rhizobia were fast growing rhizobia, lowering the pH of a defined medium. Strain AZ-M1 showed a high intrinsic resistance to 3 antibiotics among 12 tested. Strain AZ-M1 has been shown to be highly effective, fairly competitive and survive better in desert soils than strain 31A5.

<p>The microbial life of sub-Antarctic islands plays a key role in the islands ecosystem, with microbial activities providing the majority of nutrients available for primary production. Knowledge of microbial diversity is still in its infancy and this is particularly true regarding the diversity of micro-organisms in the Antarctic and sub-Antarctic regions. One particularly important functional group of micro-organisms is the diazotrophs, or nitrogen-fixing bacteria and archaea. This group have not been well studied in the sub-Antarctic region, but play an important role in the nutrient cycling of the island. This thesis explored the diversity of nitrogen-fixing organisms in the soil of different ecological habitats on the sub-Antarctic Marion Island.</p>

No description available.

This research tested the hypotheses that (a) suboptimal root-zone temperatures (RZT) limit the soybean-Bradyrhizobium N$ sb2$-fixing symbiosis primarily through an inhibition of symbiosis establishment and (b) this inhibition is modified by the genotype of micro- or macrosymbiont. Controlled environment and field experiments were conducted utilizing two soybean genotypes and six B. japonicum strains. At 19$ sp circ$C RZT fixed nitrogen levels decreased by 30-40%, predominantly due to a restriction in the latter stages of nodule development. Reductions of 10% and 30% in specific nodule activity rates at 19$ sp circ$C and 15$ sp circ$C RZT respectively, indicated nodule function to be comparatively insensitive to low RZT. Soybean genotypes did not differ in seedling nodulation or N$ sb2$-fixation under cool-soil, field or controlled environment, conditions. At all temperatures, commercial B. japonicum strain 532C was more efficient, but not effective, than strains obtained from the cool-soils of Northern Japan. Under cool-soil field conditions, two of the latter strains increased seedling nodulation and N$ sb2$-fixation.

This project was designed to assess the ability of natural sediment microbial communities and single species microbial populations to preferentially utilize inorganic forms of nitrogen (ammonium, NH4-N, and nitrate, NO3-N, specifically). The first chapter addressed two primary questions: 1) Do sediment microbial communities preferentially assimilate NH4-N or NO3-N?; and, 2) Does preferential uptake of nitrogen change with increased NH4-N or NO3-N availability? The second chapter furthered these analyses by assessing shifts in microbial nitrogen assimilation in response to sustained nitrogen enrichments. Primary questions addressed were: 1) Are microbial communities able to adapt to nitrogen enrichment and preferentially utilize a more available source?; and, 2) Are initial microbial responses to nitrogen enrichment different from sustained responses? Questions were addressed with in vitro laboratory experiments quantifying microbial activity. Overall, microbial community activity changed in response to the form of nitrogen available, enrichment type, and duration of exposure. Data demonstrate sediment microbial communities in the Midwestern US may prefer NO3-N over other forms of nitrogen. However, microbial communities became saturated with NO3-N with increases in concentrations >0.75 mg NO3-N/L. Microbial communities were able to adapt to higher nitrogen concentration and increase rates of assimilation for both NH4-N and NO3-N. Thus, microbial communities are robust in response to nitrogen increases in and ecosystem, even in high nitrogen environments like the Midwestern US. / Preferential uptake of available nitrogen forms -- Adaptive uptake in microbial communities. / Department of Biology

<p>The microbial life of sub-Antarctic islands plays a key role in the islands ecosystem, with microbial activities providing the majority of nutrients available for primary production. Knowledge of microbial diversity is still in its infancy and this is particularly true regarding the diversity of micro-organisms in the Antarctic and sub-Antarctic regions. One particularly important functional group of micro-organisms is the diazotrophs, or nitrogen-fixing bacteria and archaea. This group have not been well studied in the sub-Antarctic region, but play an important role in the nutrient cycling of the island. This thesis explored the diversity of nitrogen-fixing organisms in the soil of different ecological habitats on the sub-Antarctic Marion Island.</p>

Thesis (M.S. - Agricultural Chemistry and Soils)--University of Arizona. / Bibliography: leaves 106-129.

Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Bibliography: p. 137-190.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 76-89).

Thesis (Ph.D.)--Murdoch University, 2009. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (p. 192-223)