No description available.

Arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of terrestrial plant species with associations predominantly characterized as mutualistic. In addition to well-documented enhancement of host growth response, more recent analyses have demonstrated the conferral of host benefits under numerous biotic and abiotic stressors. However, much of the established evidence originates from studies involving limited AM fungal diversity. Accordingly, this study sought to evaluate the potential effects of inoculation on plant host physiological traits within a growth chamber environment, investigate potential correlations between host trait responses, & assess the degree of phylogenetic signal observed in trait responses due to the presence of AM fungi. Overall, inoculation did not result in meaningfully different effects in host trait responses relative to controls. The effects of unique inoculum identity were also not meaningfully different from one another, although some instances of deviation from this trend were observed. Trait correlations were also largely absent after accounting for species relatedness. Further, model selection criteria tended to endorse an effect of unique inoculum identity but was not suggestive of effects due to evolutionary history. The presently described experimental implementation of AM phylogenetic diversity, comprising 36 taxa across 8 families, contributes to a greater contextual understanding of the AM symbiosis and offers an approach suitable for future studies.

Soils contain the largest terrestrial pool of carbon (C), but the magnitude and distribution of the soil C sink may be sensitive to climate change. My dissertation aims to identify key processes that mediate patterns of belowground carbon storage across the globe and quantify the effect of environmental perturbations associated with global change on existing soil carbon stocks in peatland ecosystems. Using meta-analysis, I show that the relationship between plant growth, C allocation, and soil nutrient availability varies on a global scale and high-latitude ecosystems allocate >60% of fixed C to belowground structures. As high latitude ecosystems are warming faster than the global mean, the future of this belowground C store is potentially sensitive to climate change. In high latitude ecosystems in particular, I further show that belowground warming increases the rate of peatland carbon dioxide (CO2) and methane (CH4) losses, although CH4 emissions are more sensitive to warming than CO2 emissions, which is likely to shift the nature of greenhouse gas emissions and increase the importance of CH4 as a radiative forcing agent in the near-term. I also use a natural peatland water table gradient to identify the effect of water table reduction on peatland C and N cycling and find that microbial community shifts in C and N demand may attenuate production of C-degrading enzymes and C mineralization in the presence of plant roots and in areas with low water tables. Together, my dissertation work highlights the important role of belowground plant and microbial processes in high latitude ecosystems, and identifies the potential influence of factors associated with global change on belowground C and nutrient cycling.

Arbuscular mycorrhizal fungi (AMF) are an ancient group of obligate symbionts, colonizing the roots of over 72% of land plants, increasing the uptake of nutrients from the soil, and providing many fitness benefits to their host plants. The multinucleate and coenocytic nature of AMF have interested researchers for decades, leading to many theories of the evolution, and genetic organization of these organisms. Recent findings propose that AMF carry two types of strains, identified based on putative MAT-loci, as either homokaryotic, carrying multiple and genetically similar nuclei, or dikaryotic with co-existing nuclei deriving from two parental strains. In other fungi, hyphal fusions, or anastomosis, between compatible strains results in nuclear transfer, creating heterokaryotic spore progeny. It has been hypothesized that dikaryotic AMF strains arose from the anastomosis between compatible homokaryons harbouring different nucleotypes. The goal of this research is to determine whether anastomosis events, known to occur in other fungi, like homokaryon-homokaryon, homokaryon-dikaryon (Buller phenomenon), and/or dikaryon-dikaryon nuclear exchanges also occur in AMF. To achieve this, the anastomosis frequencies between 15 crosses of homokaryotic and dikaryotic strains of the model AMF species Rhizophagus irregularis were examined using microscopy and droplet digital PCR (ddPCR) to determine if nuclear transfer between strains is possible. Overall, these experiments build on the existing evidence of compatible interactions between strains of R. irregularis.

The mutualistic associations between Arbuscular mycorrhizal (AM) fungi and plant roots are ancient and ubiquitous across the plant kingdom, where AM fungi provide Phosphorus, Nitrogen, and water to the plant, and receive photosynthetically fixed Carbon in the form of fatty acids and sugars in return. Moreover, AM fungi are associated with increased plant resistance to both abiotic and biotic stressors such as drought and viral pathogens. Frequently used in agriculture, AM fungi are observed to increase crop yields and decrease chemical fertilizer needs for many economically important plant species. The potential to increase AM fungal effectiveness remains a driving force for current research. To determine their role in establishing and/or supporting AM symbiosis, we propose a reverse genetic study of two genes in the model legume Medicago truncatula. Based on RNA sequencing data indicating increased expression during AM symbiosis, we selected one gene that encodes for NAC TF-like protein, which belongs to a large family of plant transcription factors primarily involved in regulating the secretion of defence hormones. The second gene selected, PALM1, was recently discovered to play a role in the regulation of the trifoliate leaf structure of M. truncatula. We hypothesize that the genes under study play mechanistic roles in regulating AM fungal symbiosis and that we will observe a difference between the colonization rates of corresponding gene mutants and control groups. Firstly, we explored the involvement of the PALM1 and NAC TF genes by examining the root developmental phenotype of Medicago truncatula mutants. Secondly, we employed symbiosis assays to investigate the colonization rates of the genes in question. Results indicated that the NAC TF gene had no consistent role in the AM symbiosis, while the PALM1 gene revealed promising results, where significant increases in colonization rates were observed in PALM1 mutants throughout repeated experiments. Future research involves using this study to help pursue more effective ways to use AM fungi symbiosis in sustainable agro ecosystems.

The occurrence in Scotland of arbuscular mycorrhizal fungi (AMF) infective on Alnus glutinosa and the effects on early growth of inoculation of seedlings with AMF and Frankia were investigated. AMF characteristic of G/omiw-like fungi were detected microscopically in A. glutinosa roots from mineral and loam but not from highly organic soils. Both GJomus- and Gigaspora-like fungi were detected only in roots from sandy soils. Glasshouse experiments showed that Glomus and Gigaspora species gave higher colonisation of roots, and were of higher compatibility with the host plant, than Acutelospora or Scutettospora species. Colonisation by AMF increased nodulation by Frankia and vice versa. Inoculation with AMF alone and dual inoculation with Gigaspora rosea and Frankia inhibited growth of young A. glutinosa seedlings. Initially after inoculation, AMF colonisation was poor allowing the host to meet the requirements of both developing symbioses. Mycorrhizal plants inoculated with Frankia 15 days after AMF inoculation, were under significant stress and this delayed the beneficial effects of AMF and Frankia symbiosis. Seedlings compensated for the cost of symbiosis by developing a larger, leafy shoot in a period of 25-30 days after AMF inoculation, with or with out, Frankia nodulation. A significant increase in root length and branching detected after inoculation with AMF and Frankia must impose additional energy requirements. However, the stimulation of lateral root branching that follows AMF colonisation may facilitate nutrient uptake, thus helping the plant to overcome the disadvantages of early retardation of shoot growth. Competition with adjacent plant species for below ground space may also be enhanced thus facilitating competition for growing space with other plant species. These factors may be part of a strategy that assists the survival of very young seedlings in the field. The data obtained suggest that delaying Frankia inoculation for 3-4 weeks after inoculation with selected AMF should improve the production in Scottish nurseries of robust, well nodulated and mycorrhizal seedlings.

No description available.

Arbuscular mycorrhizal (AM) fungi are root and soil inhabiting symbionts with higher plants. The fungi are especially nutrient-function efficient in nutrient deficient soils. There have been innumerable studies of AM fungal facilitation of plant nutrient uptake in controlled environments. Comparatively little similar investigation has been undertaken in natural soils, including investigation of taxon specific nutrient-function efficiency in the phylum. Plant diversity and frequency, soil chemistry statuses, and AM spore diversity and abundance were sampled in an interrupted-belt transect in an aggrading dune sytem on west-coast India, followed by foredunes and transect nutrient amendment experiments in selected plant species. The transect extends 175 m inland from mean high-water mark (MH-WM). Examination showed nutrients were consistently deficient. A plant zonation pattern and increasing frequency over the transect were indicated, as well as decreasing pH and increasing organic matter (OM)-amendment AM species diversity gradients. Plant zonation does not correlate with soil chemistry. There was a distinct soil transition at the 175 m point and evidence of further system partition between foredune and behind-foredune regions. Plant and AM demographies bore no resemblance suggesting neither is driven by the other. Four AM genera were recovered, Acaulospora, Gigaspora and Scutellospora in high abundance, Glomus in comparatively low abundance. The two co-dominant species, A. spinosa and Gi. margarita, displayed divergent strategies in OM amendment. Certain AM taxa may be functionally associated with particular soil nutrients. There was no evidence of taxon-specific nutrient-function efficiency.

The work in this thesis aimed to demonstrate the contribution of arbuscular mycorrhizal (AM) fungi to the yield and fruit quality of field-grown processing tomatoes, and the potential to increase the sustainability of tomato production through greater fertiliser use efficiency by inoculating tomato seedlings with beneficial AM fungi. Previously, the conclusion that tomato growth is unresponsive to AM colonisation, particularly in high-P soils, has often been based on only a part of the tomato life-cycle. However, there is increasing evidence that that positive AM yield responses can occur in soils with relatively high plant-available P, and that AM responsiveness of tomato during vegetative growth may be a poor predictor of reproductive growth. A preceding industry study found that AM colonisation of field-grown processing tomatoes was very low, mostly less than 5%. The reason for the low colonisation was unclear since previous studies have shown that tomato can become relatively highly colonised by AM fungi. It was not known if farm practices, such as soil cultivation and chemical sterilisation, which have been shown to decrease AM colonisation of tomato and other crops, could have contributed to the low colonisation. Furthermore, it was unclear what contribution AM fungi were making to the yield and fruit quality of tomato in commercial production, and what their potential contribution might be if greater AM colonisation could be achieved through inoculating seedlings. Yield and fruit quality are important to tomato growers as both are used to calculate payment when the fruits are sold. Large amounts of soluble fertilisers, particularly P, are applied during tomato production with the aim of increasing yield and quality. However, fertiliser use efficiency, particularly P, on tomato farms has been identified as being low, and needing to be improved in order to increase the economic and environmental sustainability of tomato farming. Increasing P, and also other nutrients, such as Zn and Ca, in tomatoes could also help to improve agricultural sustainability by alleviating human malnutrition in developing countries and, in the case of Ca, have the potential to reduce blossom end rot, which can severely reduce marketable yield. There is considerable potential for AM fungi to assist in the supply of these nutrients to field-grown tomatoes. AM fungi are widely accepted to increase plant uptake of P. This has mostly been demonstrated in low-P soils, as increases in plant-available P are generally known to be detrimental to AM colonisation and any subsequent growth effects. However, there is increasing evidence of the ability of AM fungi to increase P uptake and yield even in high P soils. There is also good evidence of increased Zn uptake by mycorrhizal supply to plants. Evidence for increased Ca uptake in mycorrhizal plants is in comparison limited and conflicting, but has been demonstrated in some cases. It is possible that AM fungi could allow applications of these nutrients, particularly P, to be reduced while maintaining or increasing fruit yield and quality. However, the ability of indigenous or inoculated AM fungi to do so in the relatively high-P farm soils used in this project was unknown. In order to address these uncertainties a series of pot studies and a field experiment were conducted using field soils from tomato farms and an adjacent nature reserve for comparison. Data on soil characteristics from five farms, collected during the previous industry study, was analysed in conjunction with data from another farm located nearby with contrasting soil properties. Two farm soils and an unfarmed comparison were selected on the basis of their having contrasting levels of P, Zn and Ca, and pH, with the constraint that they were located within 50 km of each other to minimise travel time in the study area. The two farmed soils had a relatively high concentration of plant-available P (103 and 58 mg/kg Colwell), while plant-available P in the unfarmed soil was probably marginal to that required for healthy tomato growth (27 mg/kg Colwell). Samples of the soils were taken soon after commencement of the work and used in pot studies. Firstly, a bioassay was conducted to establish the ability of tomato to become colonised in the three field soils. AM colonisation of tomato and medic, which is known to be highly susceptible to AM colonisation, was compared between three harvests over an approx. 16 week period. Vegetative growth was also measured. The total colonisation of tomato mostly did not differ from that of medic at each harvest in any soil. Furthermore, despite the large differences in plant-available P between the three soils, colonisation and vegetative growth of tomato did not differ between soils at any harvest. In a subsequent pot experiment, the effect of colonisation by AM fungi in the three field soils on the vegetative and reproductive growth, and nutrient status of tomato was determined using the tomato mutant rmc (reduced mycorrhizal colonisation) and its progenitor 76R. A number of non-destructive vegetative and reproductive growth measurements were repeatedly measured over an approx. 24 week period. Destructive measurements were carried out at two harvests, 39 and 164 days after planting. Tomato 76R was again well colonised in all soils. Tomato rmc remained uncolonised, and was therefore an effective non-mycorrhizal control. AM colonisation had little effect on plant growth or nutrient status in any soil at the first harvest, but significant growth and nutrient responses were recorded at the second harvest. In particular, AM colonisation markedly increased vegetative growth in the unfarmed soil. AM colonisation did not affect vegetative growth in either of the farmed soils. However, AM colonisation increased reproductive growth, particularly yield over time, in all soils. AM colonisation increased shoot P concentration and content, but effects on Zn were mixed and largely inconclusive. Shoot Ca concentration and content were mostly reduced by AM colonisation. Similar patterns were observed in fruit nutrient status. The potential of pre-inoculation with AM fungi to increase AM colonisation and/or AM growth and nutrient effects in the field was considered. A commercial AM fungal inoculum was initially proposed for use, but was found to be unreliable and laboratory cultures of Scutellospora calospora and Glomus mosseae were used instead. Tomato seedlings were inoculated by amending a commercial seed-raising medium with an equal mixture of S. calospora and G. mosseae inocula. Seeds of tomato rmc, 76R and the commercial processing tomato cultivar U941 were sown and raised according to the practices followed by a commercial seedling nursery. After 9 weeks a sub-sample of inoculated seedlings of 76R and U941 had become colonised by both AM fungi, although the total colonisation was relatively low (approx. 10%). There was no difference in the shoot or root dry weights between inoculated and non-inoculated seedlings. The remaining seedlings were then used in the field experiment. Seedlings were transplanted amongst a commercial processing tomato crop on two farms and grown to maturity. A substitute farm with soil of moderate P (66 mg/kg Colwell) was used as tomatoes were no longer being grown on the initial farm with moderate P. Two P treatments, ‘normal’ and ‘reduced’ P fertilisation, were imposed in order to investigate the effect of P fertilisation on colonisation by indigenous and inoculated AM fungi, and growth and nutrient status of tomato in the field. Non-destructive growth measurements and soil core samples to assess mycorrhizal colonisation were taken mid-season (approx. 10 weeks after transplanting). Destructive growth measurements and core samples to assess colonisation were taken at harvest (approx. 19 weeks after transplanting). Colonisation of rmc was insubstantial and it again served as an effective non-mycorrhizal control to 76R. Colonisation was insubstantial in all treatments on the farm where soil had moderate plant-available P. On the other farm, where soil had relatively high plant-available P, colonisation of all plants was low mid-season, but was mostly substantial (>20%) in 76R and U941 at harvest. Low colonisation on both farms was probably the result of farming practices, particularly soil cultivation. However, a combination of inoculation and reduced P fertilisation increased colonisation. Colonisation by indigenous AM fungi had no effect on the growth or nutrient status of field grown tomatoes. In contrast, pre-inoculation with AM fungi increased fruit yield by a mean of approx. 40% in 76R and U941. This was the result of an 18% increase in the fresh weight of individual fruits and, when inoculation was combined with reduced P fertilisation, a 21% increase in the number of fruits on each plant. The increase in the number of fruits on each plant was associated with an increase in the number of flowers at the most advanced growth stage. Inoculation also increased vegetative growth, and fruit P, Zn and Ca contents. A small (4%) decrease in fruit brix was more than offset by increased yield. This study has shown that while AM fungi indigenous to tomato farm soils have the ability to substantially colonise tomato, they appear to have little effect on tomato growth, yield or nutrition in the field. In contrast, inoculation of tomato seedlings with mutualistic AM fungi during nursery production can substantially increase the growth, yield and fruit nutrient contents of field-grown tomatoes under commercial conditions. This increase could also be enhanced by a reduction in P fertilisation. Increased yield and fruit nutrient contents, and decreased P fertilisation neatly address the aims of increased agricultural sustainability. Incorporating pre-inoculation of tomato into existing farming practices has a potential to increase the productivity and sustainability of processing tomato production worldwide. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1292847 / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2007

Empresa Brasileira de Pesquisa Agropecuária / The knowledge of the level of association that occurs between diazotrophic bacteria and fungi arbusculares mycorrhizae (AMF) in grassland ecosystems may be important for the understanding of the changes caused by the addition of fertilizers containing phosphorus (P) and nitrogen (N), in the production and botanical composition of natural pastures. The objective of this study was to evaluate. (a) the occurrence of three genera of diazotrophic bacterial in the root system under fertilization with N and P, and determine the contribution of N via BNF, and (b) evaluate the behavior of the association between AMF and native grasses. Four most abundant grasses in natural grasslands of the Southern Campos in Rio Grande do Sul , Axonopus affinis, Paspalum notatum, Andropogon lateralis and Aristida laevis were grown in pots of 5 kg, in a greenhouse, two studies being conducted (A e B ). In A, two treatments were applied: 50 mg kg-1 soil P and 100 mg kg-1 of soil N (NP) and a control, being evaluated, the number of diazotrophic bacteria of the genera Azotobacter, Azospirillum and Herbaspirillum, and the contribution of BNF was determined by the technique of natural 15N abundance. In B, the treatments consisted of applying 50 mg kg-1 soil P (P), application of 50 mg kg-1 soil P and 100 mg kg-1 of soil N (NP), and a control, in both treatments mycorrhizal colonization was determined. For A, A. laevis demonstrate to be more dependent on biological N fixation than the other species. The grass P. notatum compared with other species demonstrated to be more efficient to absorb available soil N. The dry matter accumulation in shoots of the native species was higher with the application of NP. In B the mycorrhizal colonization was similar between the control, P and NP to the roots of A. lateralis and A. laevis, thus presenting a greater dependence on the mycorrhizal association. Differently, in A. affinis and P. notatum, the mycorrhizal colonization was lower when subjected to fertilization with P and NP, thus presenting a lower dependence. It is concluded for A that fertilization with N and P reduces diazotrophic colonization, increasing the production of dry matter and N content of the tissue. A. laevis showed the highest contribution of biological nitrogen fixation, since P. notatum showed higher N accumulation in soil. In relation to B, A. laevis and A. lateralis have a higher dependence on the mycorrhizal than A. affinis and P. notatum. / O conhecimento do nível de associação que ocorre entre bactérias diazotróficas e fungos micorrízicos arbusculares (FMA) nos ecossistemas campestres, pode ser importante para a o entendimento das alterações provocadas pela adição de fertilizantes, contendo fósforo (P) e nitrogênio (N), na produção e na composição botânica das pastagens naturais. O objetivo do presente trabalho foi avaliar (a) a ocorrência de três gêneros de bactérias diazotróficas no sistema radicular sob fertilização com N e P, e determinar a contribuição de N via FBN, e (b) avaliar o comportamento da associação entre FMAs e gramíneas nativas. Foram utilizadas quatro gramíneas de maior abundância nas pastagens naturais dos Campos Sulinos no Rio Grande do Sul, Axonopus affinis, Paspalum notatum, Andropogon lateralis e Aristida laevis, cultivadas em casa de vegetação, sendo conduzidos dois estudos (A e B). Em A, foram aplicados dois tratamentos: 50 mg kg-1 de solo de P + 100 mg kg-1 de N solo (NP) e uma testemunha, sendo avaliados, o número de bactérias diazotróficas dos gêneros Azotobacter, Azospirillum e Herbaspirillum, e a contribuição da FBN através da técnica da abundância natural de 15N. Em B, os tratamentos consistiram na aplicação de 50 mg kg-1 de solo de P (P); aplicação de 50 mg kg-1 de solo de P + 100 mg kg-1 de N solo (NP), e uma testemunha, em ambos foi determinada a colonização micorrízica. A espécie A. laevis demonstrou ser mais dependente da fixação biológica de N que as demais espécies. A espécie P. notatum em comparação as demais espécies, demostrou ser mais hábil em absorver o N disponível no solo. A matéria seca acumulada da parte aérea das espécies nativas foi maior com a aplicação de NP. A colonização micorrízica foi semelhante entre a testemunha, P e NP para as raízes de A. lateralis e A. laevis, apresentando assim uma maior dependência da associação micorrízica. Diferentemente, nas espécies A. affinis e P. notatum, a colonização micorrízica foi menor quando submetidas a adubação com P e NP, apresentando assim uma menor dependência. Conclui-se assim, que a adubação com N e P reduz a colonização de bactérias diazotróficas, aumentando a produção de matéria seca e teor de N no tecido. A. laevis apresentou a maior contribuição da fixação biológica de nitrogênio, já P. notatum apresentou maior acúmulo de N do solo. As espécies A. laevis e A. lateralis apresentam maior dependência da micorrização que as espécies A. affinis e P. notatum.