Copies of author's previously published works inserted. / Bibliography: leaves 189-212. / xxii, 212 leaves : ill. (some col.) ; 30cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2001

Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 55-61). Also available on the World Wide Web.

Thesis (Ph. D.) -- Lincoln University, 2009. / Also available via the World Wide Web.

Thesis (M.A.)--University of Wisconsin--Madison, 1937. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 24-27).

White clover (Trifolium repens L.) is an important component of low input pasture systems and can form effective associations with both nitrogen-fixing Rhizobium and phosphate-scavenging arbuscular mycorrhizal fungi (AMF). Understanding the genetic control of plant-AM interactions will allow clover breeders to develop genetic markers for selection of phenotypes favourable to AM symbiosis. Clover is normally an out-breeding species. Near-isogenic lines (NILs) developed from inbred lines of clover are ideal candidates for genetic studies since important agronomic traits are fixed. Four closely-related NILs provided plant material with contrasting phenotypes when inoculated with AMF Glomus mosseae. Seed-grown and clonal plants of these closely-related NILs were used to study gene expression associated with AM colonization and functioning. In order to relate plant phenotype responses specifically to changes in phosphorus availability, and ultimately to gene expression, a nutrient flowing culture system was developed in which nutrient application was constant and could be controlled. The only consistent phenotypic response discovered was a decrease in root production in response to AMF colonisation. Differential display demonstrated differences in gene expression in both leaves and roots of clover with and without AMF. These genes were mainly down-regulated in AMF plants and three were identified from a range of NILs under varying P concentrations. More apparent differences in gene expression were found in roots than in leaves, and in low rather than high AMF colonising lines. In total, 45 sequences were identified and cloned; 30 from leaves and 15 from roots. Sixteen sequences had homology with known genes, including protochlorophyllide oxido reductase and leghaemoglobin. The majority corresponded to ESTs from model legumes and from studies such as colonisation with AMF or Rhizobium, and phosphate or nitrogen starvation experiments. Six sequences were not found on any database, indicating that these corresponded to undiscovered genes either expressed or suppressed in AM white clover.

No description available.

The overall objective of this project was to investigate the effects of the symbiotic association of plants with vesicular - arbuscular mycorrhizal fungi on the intensity of intraspecific competition and its consequences on population structure I performed four main glasshouse experiments using a non - cultivated species, Rhodanthe chlorocephala ssp rosea, or a cultivated species, Trifolium subterraneum. I grew the plants at different plant densities, under different levels of resources ( phosphorus and / or light ), in environments with homogeneous and / or patchy distribution of phosphorus ( P ). In pots with homogeneous distribution of P, the addition of P to R. chlorocephala and mycorrhizal infection in T. subterraneum increased plant biomass of single plants. However, these beneficial effects were reduced by increasing plant density. Shading of plants of T. subterraneum did not generally alter these effects. Mycorrhizal symbiosis and the addition of P always increased the intensity of plant intraspecific competition. In trays with patchy or homogeneous distribution of P, mycorrhizal infection and patchy distribution of P increased the total biomass and size inequality of populations of plants of T. subterraneum. Individual biomass was determined by the local soil P concentration in patchy environments and by mycorrhizal infection in low density treatments. Mycorrhizal infection, but not patchy P distribution, increased relative competition intensity. Asymmetric or symmetric distribution of resources between plants will change these size hierarchies. The distinction between these two types of distributions has lead to two different models explaining the interaction between competition and size inequality ( degree to which the biomass is concentrated within a small fraction of the population &# 40 Weiner and Thomas 1986 ) ) the resource depletion and resource pre - emption models ( Weiner and Thomas 1986, Weiner 1988b ). In the first model ( resource depletion ) competition reduces the relative growth rate of all the individuals by the same proportion, reduces variance of growth rates and reduces variation in sizes. Thus, in this model resource acquisition is proportional to plant size ( Weiner 1990 ). This model is also called symmetric or two - sided competition and applies when competition for nutrients predominates. It predicts that at high density, plants will be smaller but the population will have less inequality than at low density ( Weiner and Thomas 1986 ). In the second model ( resource pre - emption ), competition increases the variation in relative growth rates and increases variation in sizes. Large plants obtain a more than proportional share of the resources ( relative to sizes ) ( Weiner 1990 ) and this increases their competitive ability which results in a positive feedback on plant size. This phenomenon is also called snowball cumulation, asymmetric or one - sided competition and it was observed only when competition for light was predominant ( Wilson 1988a ). This second model predicts that at high density plant populations will have more inequality than at low density ( Weiner and Thomas 1986 ). Although these two models are generally accepted, alternative analyses and recent experiments show that the degree of asymmetry of the interaction depends on the spatial and temporal distribution of the resource, the spatial distribution of the individuals in the population, neighbourhood competition and the mobility of the resource ( Huston 1986 ; Miller and Weiner 1989, Weiner 1990, Bonan 1991 ). Weiner ( 1990 ) suggested that if nutrients are distributed homogeneously and the uptake is proportional to root size, the competitive interaction will be more symmetric, whereas if patches with more nutrients can be reached by large individuals, asymmetric competition will predominate. This hypothesis has not been tested yet. Turner and Rabinowitz ( 1983 ) found that populations with an initial random spatial distribution of individuals had an unexpected increase in size inequality. My results emphasise that the main effects of mycorrhizas at the individual level cannot be expected to be apparent at the population level, because of the influence of density - dependent processes. However, infected individuals with a strong response to the symbiosis would have an advantage in situations of competition. This scenario can explain the maintenance of the symbiotic ability even under conditions such as dense populations, where there is no obvious advantage of the symbiosis at the population level. / Thesis (Ph.D.)--Department of Soil and Water, 1998.

The overall objective of this project was to investigate the effects of the symbiotic association of plants with vesicular - arbuscular mycorrhizal fungi on the intensity of intraspecific competition and its consequences on population structure I performed four main glasshouse experiments using a non - cultivated species, Rhodanthe chlorocephala ssp rosea, or a cultivated species, Trifolium subterraneum. I grew the plants at different plant densities, under different levels of resources ( phosphorus and / or light ), in environments with homogeneous and / or patchy distribution of phosphorus ( P ). In pots with homogeneous distribution of P, the addition of P to R. chlorocephala and mycorrhizal infection in T. subterraneum increased plant biomass of single plants. However, these beneficial effects were reduced by increasing plant density. Shading of plants of T. subterraneum did not generally alter these effects. Mycorrhizal symbiosis and the addition of P always increased the intensity of plant intraspecific competition. In trays with patchy or homogeneous distribution of P, mycorrhizal infection and patchy distribution of P increased the total biomass and size inequality of populations of plants of T. subterraneum. Individual biomass was determined by the local soil P concentration in patchy environments and by mycorrhizal infection in low density treatments. Mycorrhizal infection, but not patchy P distribution, increased relative competition intensity. Asymmetric or symmetric distribution of resources between plants will change these size hierarchies. The distinction between these two types of distributions has lead to two different models explaining the interaction between competition and size inequality ( degree to which the biomass is concentrated within a small fraction of the population &# 40 Weiner and Thomas 1986 ) ) the resource depletion and resource pre - emption models ( Weiner and Thomas 1986, Weiner 1988b ). In the first model ( resource depletion ) competition reduces the relative growth rate of all the individuals by the same proportion, reduces variance of growth rates and reduces variation in sizes. Thus, in this model resource acquisition is proportional to plant size ( Weiner 1990 ). This model is also called symmetric or two - sided competition and applies when competition for nutrients predominates. It predicts that at high density, plants will be smaller but the population will have less inequality than at low density ( Weiner and Thomas 1986 ). In the second model ( resource pre - emption ), competition increases the variation in relative growth rates and increases variation in sizes. Large plants obtain a more than proportional share of the resources ( relative to sizes ) ( Weiner 1990 ) and this increases their competitive ability which results in a positive feedback on plant size. This phenomenon is also called snowball cumulation, asymmetric or one - sided competition and it was observed only when competition for light was predominant ( Wilson 1988a ). This second model predicts that at high density plant populations will have more inequality than at low density ( Weiner and Thomas 1986 ). Although these two models are generally accepted, alternative analyses and recent experiments show that the degree of asymmetry of the interaction depends on the spatial and temporal distribution of the resource, the spatial distribution of the individuals in the population, neighbourhood competition and the mobility of the resource ( Huston 1986 ; Miller and Weiner 1989, Weiner 1990, Bonan 1991 ). Weiner ( 1990 ) suggested that if nutrients are distributed homogeneously and the uptake is proportional to root size, the competitive interaction will be more symmetric, whereas if patches with more nutrients can be reached by large individuals, asymmetric competition will predominate. This hypothesis has not been tested yet. Turner and Rabinowitz ( 1983 ) found that populations with an initial random spatial distribution of individuals had an unexpected increase in size inequality. My results emphasise that the main effects of mycorrhizas at the individual level cannot be expected to be apparent at the population level, because of the influence of density - dependent processes. However, infected individuals with a strong response to the symbiosis would have an advantage in situations of competition. This scenario can explain the maintenance of the symbiotic ability even under conditions such as dense populations, where there is no obvious advantage of the symbiosis at the population level. / Thesis (Ph.D.)--Department of Soil and Water, 1998.

Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1999. / Bibliography: leaves 135-156.

Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Soil and Land Systems, 2005? / "August, 2004" Title from t.p. on PDF file; viewed 29 June 2005. Includes bibliographical references. Also available in a print form.