Les plantes terrestres vivent en association avec des champignons du sol, formant ce que l’on appelle des symbioses mycorhiziennes. Elles échangent du carbone (photosynthétats) contre de l’eau et des minéraux. Ce mutualisme est toutefois troublé par certaines plantes, appelées mycohétérotrophes, capables de soutirer du carbone à leurs symbiontes fongiques. Le plus souvent non photosynthétiques, elles dépendent alors entièrement des champignons mycorhiziens. Certaines ont en revanche conservé la photosynthèse et obtiennent leur carbone par ces deux voies, on les appelle mixotrophes. Cette thèse est consacrée à l’étude des plantes mycohétérotrophes et mixotrophes chez les orchidées, avec des éléments de comparaison chez les éricacées. Les différents travaux qui la structurent précisent la phylogénie de certains groupes clés, s’intéressent aux évolutions génomiques, métaboliques et physiologiques accompagnant ces modes de nutrition originaux, et à leur sensibilité face aux conditions environnementales. / Terrestrial plants live in collaboration with soil fungi, forming associations called mycorrhizal symbioses. They exchange carbon (photosynthates) for water and nutrients. This mutualism is however disrupted by some plants, called mycoheterotrophs, which are able to obtain carbon from their fungal symbionts. Non-photosynthetic most of the time, then they entirely depend on mycorrhizal fungi. Some yet have retained photosynthesis and acquire carbon from these two ways, we called them mixotrophs. This PhD thesis is dedicated to the study of mycoheterotrophic and mixotrophic plants in orchids, with points of comparison in Ericaceae. This dissertation is structured around different kinds of work, which clarify the phylogeny of some key lineages, provide insights into the genomic, metabolic and physiologic evolution going along with these unusual nutrition types, and question how they respond to environmental parameters.

Os crustáceos estão entre os invertebrados marinhos mais diversos e tendem a se associar com outros organismos a fim de encontrar abrigo, oferta de alimento e um lugar seguro para reprodução. Aspectos reprodutivos como fecundidade, tamanho dos embriões e energia investida na reprodução são os principais parâmetros para a compreensão da história natural de uma espécie e/ou população. Assim, esse trabalho foi desenvolvido no sentido de investigar tais parâmetros e a influência do tipo de substrato ocupado. A espécie utilizada como modelo de estudo foi o caranguejo porcelanídeo Pachycheles monilifer coletado em dois substratos biológicos diferentes, no briozoário Schizoporella errata no píer do Itaguá e no poliqueto Phragmatopoma caudata na praia Grande, ambas as paias localizadas em Ubatuba, litoral norte de SP. Somente os embriões em estágio inicial de desenvolvimento foram utilizados para os cálculos de fecundidade e investimento reprodutivo (RO). Os embriões foram contados e medidos sob esteromicroscópio. Para obtenção do RO foram utilizados os pesos secos das fêmeas ovígeras e das massas de embriões, previamente secos em estufa. Além dos aspectos reprodutivos, análises de distância genética também foram realizadas pelo sequenciamento de genes mitocôndrias (16S e COI) de exemplares de P. monilifer. A estimativa da porcentagem de variação genética intra e interespecífica, a possibilidade de fluxo gênico entre indivíduos de diferentes praias do estado de São Paulo foram verificadas. A partir desses dados confirmou-se a validade da espécie, assim como o fluxo gênico contínuo entre indivíduos dessas duas praias. A baixa divergência genética permite concluir que as diferenças reprodutivas encontradas são, portanto um reflexo das condições proporcionadas pelo ambiente. Os animais simbiontes do briozoário, assim como as fêmeas ovígeras, são maiores que os associados ao poliqueta e também possuem maior fecundidade e investimento reprodutivo, porém não foram encontradas diferenças em relação ao tamanho dos embriões. No substrato do briozoário o estresse reprodutivo parece ser menor que no substrato do poliqueto, já que aquele substrato proporciona um ambiente fisicamente mais estável para os organismos simbiontes. No substrato do poliqueto, além do alto hidrodinamismo local, o espaço disponível na colônia parece ser mais restrito e pode limitar o tamanho de seus habitantes. Os animais simbiontes do briozoário parecem não serem influenciados por fatores externos à colônia, entretanto o mesmo não foi observado nos simbiontes do poliqueto. Tais diferenças reprodutivas refletem o tipo de substrato ocupado, evidenciando a plasticidade fenotípica da espécie para uma melhor adaptação local. / The crustaceans are the most diverse of the marine invertebrates and many of them tend to associate with other organisms where they can find shelter, food supply and a safe place to reproduce. Reproductive traits as fecundity, egg size and reproductive output (RO) are the most important aspects to understand the species life history. This study aimed to investigate the reproductive traits in relation to the substrate that the organisms live. The studied species used as model was the porcellanid crab Pachycheles monilifer that was collected in two different substrates, one of them is the bryozoan Schizoporella errata at the Itaguá beach and the other is the polychaete Phragmatopoma caudata at Grande beach, both are located in Ubatuba, northern coast of São Paulo. Only the initial stage of eggs was used to estimate the crab fecundity and RO. The eggs were counted and measured in a stereomicroscope. To obtain the RO the female and the egg mass dry weight, which were previously dried in an oven, were used. Besides the reproductive aspects, the genetic distance between the organisms was valued with partial sequences of the mitochondrial genes 16S and COI. The estimate of the intra and interspecific genetic variation and the possibility of gene flow between the individuals from the beaches in SP were analyzed too. Therefore, with all these analyses it was possible to confirm that the species is valid and that there is gene flow among the populations. The low genetic divergence allowed us to conclude that the different reproductive traits found among the populations were due to the different substrates that the organisms inhabit. The bryozoan symbionts are larger than the polychaete symbionts as well as the females fecundity and the RO, but there is no difference in egg size. In the bryozoan substrate it seems like the physical stress is smaller than in polychaete and it promotes a more stable habitat for the crabs reproduce. In the polychaete substrate, beyond the high hydrodynamic location, the available space in the colony appears to be narrower, which could limit the size of its inhabitants. The bryozoan symbionts do not seem to be influenced by the external factors of the colony, though the same was not observed in the polychaete colony. Such differences in reproduction reflect the kind of substrate inhabited, highlighting the phenotypic plasticity of the species to a local better adaptation.

The division Percomorphacea encompasses a major fraction of the extant fish diversity, including over half of all known ray-finned fishes and approximately one fourth of the living vertebrates. The interrelationships among the major percomorphacean lineages are still far from a satisfactory resolution. Among the 30 percomorphacean orders, Stromateiformes encloses 77 extant species distributed into 16 genera and six families - Amarsipidae, Ariommatidae, Centrolophidae, Nomeidae, Stromateidae, and Tetragonuridae. Members of this order are globally distributed in temperate and tropical oceans and exhibit two extraordinary morphological specializations: the presence of a pharyngeal sac and of a subdermal canal plexus over the head and trunk. The phyletic status of Stromateiformes has never been adequately tested on morphological grounds and the monophyly of the order has been recently rejected by multiple molecular analyses. Moreover, stromateiforms have been indecisively aligned with disparate percomorphacean taxa by both morphology- and molecular-based studies. The present work delved into these questions and presented a comprehensive phylogenetic revision of Stromateiformes based on an exhaustive analysis of 218 phenotypic characters and 66 terminal taxa encompassing all valid stromateiform genera, as well as all percomorphacean families somehow aligned with stromateiforms in prior studies. The resulting topology retrieves the order as monophyletic, supported by four unequivocal synapomorphies. Amarsipidae, the only stromateiform lacking a pharyngeal sac, is resolved as the sister group of the remaining members of the order. Centrolophidae is not monophyletic, with five of its genera grouped into a basal clade, whereas the other two appear as successive sister groups of a clade containing the remaining stromateiform families. All these families are recovered as monophyletic with the following cladistic arrangement: Nomeidae (Stromateidae (Tetragonuridae, Ariommatidae)). A clade composed by Bramidae and Caristiidae is herein hypothesized the sister group of stromateiforms, although this arrangement is supported by only a single unequivocal synapomorphy. The present study further hypothesizes that the remarkable symbiotic relationship between juvenile stromateiforms and gelatinous invertebrates (e.g. medusa and salps) is probably associated with the evolution of some of its most remarkable morphological specializations, such as the presence of dendritic pyloric caeca, subcutaneous canal plexuses, and the pharyngeal sac. / A divisão Percomorphacea engloba a maior diversidade de peixes viventes, somando mais da metade dos peixes de nadadeiras raiadas e o equivalente a praticamente um quarto de todos os vertebrados atuais. Entretanto, as interrelações entre as maiorias das linhagens de Percomorphacea ainda está longe de uma resolução satisfatória. Dentre as 30 ordens de Percomorphacea reconhecidas atualmente, Stromateiformes agrupa 77 espécies organizadas em 16 gêneros e seis famílias - Amarsipidae, Ariommatidae, Centrolophidae, Nomeidae, Stromateidae e Tetragonuridae. Membros dessa ordem exibem distribuição global em águas tropicais e temperadas, tanto em ambientes pelágicos ou costeiros, e são tradicionalmente agrupados por apresentar duas especializações morfológicas singulares: a presença de uma bolsa faringeana, e de uma rede de canais subdérmicos sobre a cabeça e o tronco. O status filético de Stromateiformes nunca foi testado de maneira apropriada com base em dados morfológicos, e seu monofiletismo tem sido rejeitado por diferentes análises filogenéticas pautadas em dados moleculares. Além disso, análises morfológicas e moleculares têm se mostrado indecisivas quanto às relações de Stromateiformes com outros Percomorphacea. O presente estudo se propôs a investigar estas questões e apresentou uma ampla revisão filogenética de Stromateiformes baseada uma análise exaustiva de 218 caracteres fenotípicos e 66 táxons terminais, o que inclui todos os gêneros válidos de Stromateiformes bem como todas as famílias de Percomorphacea que de alguma maneira já foram alinhadas à ordem. A topologia resultante indica a ordem como monofilética e suportada por quatro sinapomorfias. Amarsipidae, o único representante de Stromateiformes a não apresentar uma bolsa faringeana, é posicionado como grupo irmão dos demais membros da ordem. Centrolophidae não é monofilético, com cinco de seus gêneros agrupados em um clado basal, enquanto outros dois aparecem como grupos irmãos sucessivos de um clado composto pelas demais famílias de Stromateiformes Todas estas famílias são recuperadas como monofiléticas, arranjadas da seguinte maneira: Nomeidae (Stromateidae (Tetragonuridae, Ariommatidae)). Um clado composto por Bramidae e Caristiidae é aqui hipotetizado como sendo o grupo irmão dos Stromateiformes, apesar desse arranjo ser suportado por apenas uma sinapomorfia não ambígua. O presente estudo ainda apresenta uma hipótese de que a relação simbiótica singular entre juvenis de Stromateiformes e outros invertebrados gelatinosos (e.g. medusas e salpas) está provavelmente associado com a evolução de algumas das mais notáveis especializações morfológicas do grupo, tais como os cecos pilóricos arranjados numa massa dendrítica, a presença de um plexo de canais subcutâneos, e a presença de uma bolsa faringeana.

Insetos são os organismos multicelulares mais bem-sucedidos no ecossistema terrestre e sua riqueza se deve, em parte, à simbiose com microrganismos. Geradora de diversidade fenotípica, a comunidade microbiana associada a insetos permite a manutenção de fenótipos complexos capazes de colonizar novos nichos e de se adaptar a fatores de estresse. A relevância da relação de simbiose na ordem Lepidoptera, todavia, tem sido questionada em função da alta variabilidade da comunidade bacteriana associada aos seus representantes. Tendo como modelo de estudo lagartas do gênero Spodoptera (Lepidoptera: Noctuidae), esse trabalho teve por objetivo melhor compreender a composição e diversidade da microbiota associada ao intestino de lepidópteros, assim como verificar o efeito da pressão de seleção direcionada à resistência na sua estrutura e capacidade de utilização de inseticidas como fonte de carbono. Para isso, foi realizada a análise metagenômica da comunidade microbiana intestinal de quatro espécies do gênero Spodoptera assim como de cinco populações naturais de S. frugiperda e de linhagens suscetível e resistentes desse inseto praga. Foram avaliadas linhagens de S. frugiperda resistentes aos inseticidas spinosad, chlorpyrifos, lambda-cyhalothrin, flubendiamide, teflubenzuron e à toxina de Bacillus thuringiensis Cry1A.105+Cry2Ab2. A análise da composição, riqueza e capacidade da comunidade bacteriana utilizar inseticidas foi baseada na determinação de índices de diversidade alfa e beta, no isolamento de bactérias intestinais em meio seletivo e na análise do potencial de crescimento dos isolados em inúmeros inseticidas. Nossos resultados indicam a importância da microbiota intestinal para esse gênero de Lepidoptera. Bactérias do gênero Enterococcus foram predominantes em todas as populações de Spodoptera analisadas, independentemente da espécie, dieta ou pressões de seleção às quais as lagartas foram expostas. Populações naturais de S. frugiperda apresentaram um microbioma mais diverso e com maior número de bactérias capazes de metabolizar inseticidas. A diversidade do microbioma, assim como a presença e capacidade de bactérias utilizarem inseticidas como fonte de carbono para o seu crescimento foram influenciadas pelo nível de exposição a tais compostos, demonstrando que, assim como o hospedeiro, a microbiota intestinal também se encontra em pressão de seleção direcionada a resistência. / Insects are the most successful multicellular organisms in the terrestrial ecosystem and their richness is partially due to symbiosis with microorganisms. The microbial community associated with insects allows the maintenance of complex phenotypes capable of colonizing new niches and adapting to stressors. The relevance of symbiosis in Lepidoptera, however, has been questioned due to the high variability of the bacterial community associated with its representatives. Using Spodoptera larvae as a model, this work aimed to better understand the composition and diversity of the gut microbiota associated with Lepidoptera, as well as to verify the effects of the selection pressure with insecticides in the microbial gut structure and the ability of members of the community to metabolize insecticides as carbon source. Thus, we performed a metagenomic analysis of the gut microbial community of four species of the genus Spodoptera (Lepidoptera: Noctuidae), as well as for five natural populations of S. frugiperda and susceptible and resistant strains of this pest. Strains of S. frugiperda resistant to the insecticides spinosad, chlorpyrifos, lambda-cyhalothrin, flubendiamide, teflubenzuron and Bacillus thuringiensis toxin Cry1A.105 + Cry2Ab2 were evaluated. The analysis of the composition, richness and ability of the bacterial community to metabolize insecticides were carried out through alpha and beta diversity indexes, isolation of intestinal bacteria in selective medium and analysis of the growth potential of isolates in multiple insecticides. Our data indicate the importance of symbiosis for S. frugiperda. Enterococcus prevailed in all populations analyzed, regardless of the species of Spodoptera, food source or selection pressure that the larvae were exposed. Microbial diversity and ability to metabolize insecticides were higher in natural populations exposed to a range of stressors in the field. The diversity of the gut microbial community associated to Spodoptera frugiperda, as well as the ability of its members to metabolize insecticides, were influenced by the degree of exposure to insecticides, showing that, like the host, the gut microbiota is also under selection pressure to resistance.

Kwan Yiu Chi Derek. / "Architecture Department, Chinese University of Hong Kong, Master of Architecture Programme 1997-98, design report." / Chapter 1.0 --- ABSTRACT / Chapter 2.0 --- BACKGROUND / Chapter 2.1 --- Historic Background --- p.2 / Chapter 2.2 --- Recent Political Changes --- p.2 / Chapter 2.3 --- Site --- p.3 / Chapter 2.4 --- Clients --- p.4 / Chapter 2.5 --- Users --- p.4 / Chapter 2.6 --- Program --- p.5 / Chapter 2.7 --- Schedule of Accomodations --- p.5 / Chapter 3.0 --- CONTEXT STUDIES / Chapter 3.1 --- Kowloon Urban Growth Studies --- p.6 / Chapter 3.2 --- Shenzhen Urban Growth Studies --- p.7 / Chapter 3.3 --- Pedestrain Movement Path Study --- p.8 / Chapter 4.0 --- FORM & SPACE STUDIES / Chapter 4.1 --- Morphological Study of Symbiosis --- p.10 / Chapter 4.2 --- Border Crossing Circulation Study --- p.12 / Chapter 4.3 --- Border Crossing Landscape Study --- p.13 / Chapter 4.4 --- Building Intrusion Study --- p.14 / Chapter 4.5 --- Dynamic Form Study --- p.15 / Chapter 5.0 --- "SUMMARY OF CONTEXT, FORM & SPACE STUDIES " / Chapter 5.1 --- Site Plan --- p.19 / Chapter 5.2 --- Lower and Upper Floor Plans --- p.20 / Chapter 5.3 --- Longitudinal and Cross Sections --- p.21 / Chapter 6.0 --- TECHNICAL STUDIES / Chapter 6.1 --- Structural Frame Study --- p.22 / Chapter 6.2 --- QuickSlice and Rapid Prototyping --- p.24 / Chapter 6.3 --- Summary of Technical Studies & Materials --- p.25 / Chapter 7.0 --- APPENDIX / Chapter 7.1 --- Summary of Experimental Studies --- p.26

Yip Hong Ming Angus. / "Architecture Department, Chinese University of Hong Kong, Master of Architecture Programme 1997-98, design report." / Includes bibliographical references (leaf 44 (2nd gp.)). / Chapter Chapter 0 --- Prologue --- p.1-6 / Point of Departure / Synopsis / Chapter Chapter 1 --- Healing the city --- p.7-13 / Site & context / Senses of contradiction / "Senses of ""in - between""" / The potential of the site / Site Section & Site issue / Summary / Intervention (Part ore) Bridging the gap Design approach --- p.14-18 / Design approach / Precedent / Architectural languages / Master layout plan / Environment Upgrade / Bridge Performances / Intervention (Part two) Alienation --- p.19-21 / Ideas of Trans-program Building / User analysis / Funcitonal relationship / Chapter Chapter 2 --- Sensation of wall --- p.22-29 / Phasing development / Concept development / Concept model / Interim development / Interim Presentation / Chapter Chapter 3 --- In between space Illusion concepts Building Sections --- p.30-34 / Chapter Chapter 4 --- Illusion one :[outside/inside] --- p.35-37 / Chapter Chapter 5 --- Illusion two :[Supernatural/Superartifical] --- p.38-40 / Chapter Chapter 6 --- Illusion three ：[Fitness center/Shelthered workshop] --- p.41-43 / Chapter Chapter 7 --- llusion four ：[Stone in the air] --- p.44-49

No description available.

Coral reefs worldwide are experiencing unprecedented and rapid declines. However, deeper, mesophotic coral ecosystems (MCEs; 30–150 m) may act as refuges for coral species, providing larvae to recolonize degraded shallow reefs. This study assessed the genetic connectivity of shallow and mesophotic Montastraea cavernosa populations on the Belize Barrier Reef and the community structure of their endosymbiotic algae (Family Symbiodiniaceae) across a fine-scale depth gradient (10, 16, 25, 35 m). Evaluation of nine polymorphic microsatellite markers demonstrated that relatively shallow (10 and 16 m) M. cavernosa populations were genetically distinct from relatively deep (25 and 35 m) populations. High throughput sequencing of ribosomal coding DNA from Symbiodiniaceae communities of M. cavernosa revealed differences in community structure across depth, with shallow-specialist and depth-generalist community profiles. This research provides important information for the management of distinct deep and adds to the body of research on the understudied MCEs of the Mesoamerican Reef. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

The rhizobium – legume symbiosis is a complex process that involves genetic cooperation from both bacteria and plants. Previously, our lab described naturally occurring accessory plasmids in rhizobia that inhibit this cooperation. A transposon mutagenesis was performed on the plasmids to detect the genetic factor that blocked nitrogen fixation. Several of the plasmids were found to possess a replication operon that when disrupted by transposon insertion, restored symbiotic function. This study describes an in-depth investigation into one of those plasmids, pHRC377, and into its replication operon. The operon, which we have called repA2C2, comes from the repABC family of replication and partitioning systems commonly found in alphaproteobacteria. In this study we show that this operon is not necessary for pHRC377 replication in LB culture or free living cells, but is necessary for plasmid amplification in the plant, specifically during rhizobial differentiation into nitrogen fixing bacteroids. We also show how the other repABC type operons on pHRC377 function in relation to plasmid maintenance and copy number during endoreduplication and how they do not have the same phenotypic effect as repA2C2.

The overall objective of the work presented in this thesis was to investigate roles of arbuscular mycorrhizal ( AM ) fungi in growth and phosphorus ( P ) nutrition of wheat ( Triticum aestivum L. ) in a highly calcareous soil from the Eyre Peninsula, South Australia. The soil used for this study is one of the main soil types used for wheat production in South Australia. It is severely P - deficient, but plant responses to conventional fertiliser application are poor. Although the total P and Colwell - extractable P contents of the soil are high, the resin - extractable P content is very low. Resin - extractable P is better able to predict P availability for plant growth than Colwell - extractable P. The soil is also strongly P - fixing. Moderate levels ( about 20 mg kg [superscript minus 1] ) of resin - extractable P for wheat could only be achieved by adding high rates ( up to 100 mg kg [superscript minus 1] ) of CaHPO4 in this soil. A bioassay with wheat showed that it can be highly colonised by AM fungi in the soil. AM fungi have been shown to improve P nutrition of plants, particularly in nutrient poor soils. They may thus be important for wheat grown in the soil with low amounts of plant - available P such as the one used. The first part of the work involved conventional pot experiments. Effects of AM fungi on wheat were compared between sterilised soil and non - sterile soil, sterilised soil inoculated with non - sterile soil or with Glomus intraradices or noninoculated, with different soil / sand mixes. Colonisation of wheat at 8 weeks was high, with about 75 % of root length colonised for indigenous fungi and 55 % for Glomus intraradices, regardless of the soil treatments. Growth and P uptake of wheat were significantly increased by both indigenous fungi and G. intraradices, irrespective of soil / sand mixes. Effects of indigenous fungi on plant growth were larger in sterilised and inoculated soil than in non - sterile soil. In sterilised soil, increases of plant growth by AM fungi were higher with G. intraradices than with indigenous fungi. Dilution of the soil by mixing with sand reduced plant growth and P uptake of both AM and non-mycorrhizal ( NM ) plants. In another experiment, responses of wheat to AM fungi and P supply were compared with those of clover. Plants were inoculated with four different AM fungi. Colonisation of wheat was lower than clover. Although suffering from P deficiency, NM wheat ( 6 weeks ) grew relatively well with no added P ( P0 ) and application of P at 100 mg kg [superscript minus 1] ( P100 ) increased the dry weight ( DW ). Shoot P concentrations increased with P application and there were positive effects of all AM fungi at P100. In contrast, NM clover ( 8 weeks ) grew very poorly at P0 and did not respond to P application. Clover responded positively to all AM fungi at both P levels, associated with increases in P uptake. The results showed that responses of wheat to AM inoculation and P supply were quite different from those of clover, and emphasized the different abilities of the two species to access P in the very high P - fixing soil used. Responses of two wheat cultivars ( Brookton and Krichauff ) to AM fungus ( G. intraradices ) were also evaluated with different P supplies at two developmental stages ( vegetative and maturity ). Colonisation by G. intraradices of both cultivars was well established at 6 weeks ( ~ 50 % in P0 plants ) and continued to increase up to maturity ( ~ 70 % ), but decreased greatly at both harvests as P supply was increased ( up to 150 mg P kg [superscript minus 1] ). Addition of P significantly increased plant growth, grain yield and P uptake irrespective of cultivar and harvest time, and the optimum soil P for grain yield was 100 mg kg [superscript minus 1]. In both cultivars, a growth depression in AM plants occurred at 6 weeks at all P levels, but this disappeared at 19 weeks with added P. At P0, AM plants produced lower grain yield per plant, but with higher P supply, AM plants produced higher grain yields than NM plants. There was a significant positive effect of AM on grain P concentration at P0, but not at other P levels. Brookton was somewhat more P efficient than Krichauff, and the latter responded more to AM fungi. The results showed that responses of wheat to AM fungi and P supply changed during development. Growth depression induced by AM fungi in low P soil was overcome by addition of moderate amounts of P, resulting in significant increases in grain yield in AM plants. Additional approaches were used to help determine the roles of AM fungi in wheat growth and nutrition. The effects of plant density were tested, as it was expected that increasing density might decrease the negative effects of AM fungi on wheat growth. Large growth depressions were induced by both G. intraradices and Gigaspora margarita in wheat grown at low density, although % colonisation by G. intraradices was higher than by Gi. margarita. With increasing plant density, the growth depressions were smaller, indicating that competition modulates growth responses. Although there may be effects due to competition for soil P, it is clear that with increasing plant biomass per unit soil volume, the AM fungal biomass did not increase in proportion ; in fact, hyphal length density decreased. Accordingly, costs of AM in terms of organic carbon loss per plant decreased with increasing plant density, thus mitigating the growth depression. The results add to the increasing body of evidence that mycorrhizal growth responses of plants grown singly may not apply at the population or community level as in crops. Two compartmented pot systems were used to examine whether the fungal hyphae deliver the P into the plants even in the absence of positive growth responses. An experiment in which plants were constricted in a mesh bag, but hyphae of AM fungi could explore a large soil volume was carried out. Results suggested that AM fungi helped the plants acquire P, although mesh bags did not remove AM growth depression. The experiments in which AM fungi were supplied with [superscript 32]P in a small soil compartment to which only hyphae had access showed that a considerable amount of P was delivered to wheat plants via AM fungi. The original aim was to calculate the percentage of total P entering the plants via the AM pathway. However, realistic values were not obtained probably because of difficulties of determining plant-available P and uneven distribution of hyphae in the soil. It is also possible that plants and AM fungi access different P pools. This study demonstrated the potential roles of AM fungi in growth and P nutrition of wheat grown in the highly calcareous soil from the Eyre Peninsula, South Australia. Further studies on the effects of the interactions between AM fungi and wheat in the field are needed to assess the contribution of AM fungi to plant nutrition. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.